docs: add HattoriHenzo as a contributor for code (#1981)

* docs: update README.md [skip ci]

* docs: update .all-contributorsrc [skip ci]

Co-authored-by: allcontributors[bot] <46447321+allcontributors[bot]@users.noreply.github.com>

.circleci/config.yml

@@ -1,7 +1,6 @@
-#!/bin/bash
 #
 # The MIT License
-# Copyright © 2014-2019 Ilkka Seppälä
+# Copyright © 2014-2021 Ilkka Seppälä
 #
 # Permission is hereby granted, free of charge, to any person obtaining a copy
 # of this software and associated documentation files (the "Software"), to deal
@@ -22,25 +21,32 @@
 # THE SOFTWARE.
 #
 
+version: 2
 
-# Clone gh-pages
-git clone https://github.com/iluwatar/java-design-patterns-web.git
-cd java-design-patterns-web
+jobs:
+  sonar-pr:
+    docker:
+      - image: circleci/openjdk:11-node
+    steps:
+    - checkout
+    - restore_cache:
+        key: jdp-sonar-pr-{{ checksum "pom.xml" }}
+    - run: |
+        if [ -n "${CIRCLE_PR_NUMBER}" ]; then
+          MAVEN_OPTS="-Xmx3000m" xvfb-run ./mvnw -B clean verify org.sonarsource.scanner.maven:sonar-maven-plugin:sonar \
+             -Dsonar.pullrequest.key=${CIRCLE_PR_NUMBER} \
+             -Dsonar.pullrequest.branch=${CIRCLE_BRANCH} \
+             -Dsonar.pullrequest.base=master
+        else
+          echo "No Sonar PR analysis as this is not a pull request"
+        fi
+    - save_cache:
+        key: jdp-sonar-pr-{{ checksum "pom.xml" }}
+        paths:
+        - ~/.m2
 
-# Init and update submodule to latest
-git submodule update --init --recursive
-cd 30-seconds-of-java
-git pull origin master
-cd ../patterns
-git pull origin master
-cd ../programming-principles
-git pull origin gh-pages
-cd ..
-
-# Setup Git
-git config user.name "Travis-CI"
-git config user.email "travis@no.reply"
-
-git add .
-git commit -m ":sparkles: :up: Automagic Update via Travis-CI"
-git push --quiet "https://${GH_TOKEN}:x-oauth-basic@github.com/iluwatar/java-design-patterns-web.git" master > /dev/null 2>&1
+workflows:
+  version: 2
+  all:
+    jobs:
+    - sonar-pr

.github/workflows/maven-ci.yml

@@ -0,0 +1,101 @@
+#
+# The MIT License
+# Copyright © 2014-2021 Ilkka Seppälä
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in
+# all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+# THE SOFTWARE.
+#
+
+# This workflow will build a Java project with Maven
+# For more information see: https://help.github.com/actions/language-and-framework-guides/building-and-testing-java-with-maven
+
+# We are using two jobs here for testing our code on the latest JDK 11 build as well as a more satble build version of 11.0.3
+# You can see the full discussion here https://github.com/iluwatar/java-design-patterns/pull/1868#issue-1029459688
+
+name: Java CI
+
+on:
+  push:
+    branches: [ master ]
+
+
+jobs:
+
+  # This Workflow Job will build this project and run Sonar analysis using JDK 11.0.3
+  build-and-analyze:
+
+    name: Build and Run Sonar analysis on JDK 11.0.3
+    runs-on: ubuntu-20.04
+    steps:
+
+    - name: Checkout Code
+      uses: actions/checkout@v2
+      with:
+        # Disabling shallow clone for improving relevancy of SonarQube reporting
+        fetch-depth: 0
+
+    - name: Set up JDK 11.0.3
+      uses: actions/setup-java@v2
+      with:
+        java-version: 11.0.3
+        distribution: 'zulu'
+        cache: 'maven'
+
+    # Cache Sonar packages which as used to run anaylysis and collect metrics
+    - name: Cache SonarCloud packages
+      uses: actions/cache@v2
+      with:
+        path: ~/.sonar/cache
+        key: ${{ runner.os }}-sonar
+        restore-keys: ${{ runner.os }}-sonar
+
+    # Some tests need screen access
+    - name: Install xvfb
+      run: sudo apt-get install -y xvfb
+
+    - name: Build with Maven and run SonarQube analysis
+      run: xvfb-run ./mvnw clean verify org.sonarsource.scanner.maven:sonar-maven-plugin:sonar
+      env:
+        # These two env variables are needed for sonar analysis
+        GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        SONAR_TOKEN: ${{ secrets.SONAR_TOKEN }}
+
+  
+  # This Workflow Job is going to build the project on the latest stable JDK 11
+  build:
+
+    name: Build and Test on JDK 11
+    runs-on: ubuntu-20.04
+    steps:
+
+    - name: Checkout Code
+      uses: actions/checkout@v2
+
+    - name: Set up JDK 11 (Latest)
+      uses: actions/setup-java@v2
+      with:
+        java-version: 11
+        distribution: 'zulu'
+        cache: 'maven'
+
+    # Some tests need screen access
+    - name: Install xvfb
+      run: sudo apt-get install -y xvfb
+
+    - name: Build with Maven
+      run: xvfb-run ./mvnw clean verify

.github/workflows/maven-pr-builder.yml

@@ -0,0 +1,59 @@
+#
+# The MIT License
+# Copyright © 2014-2021 Ilkka Seppälä
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in
+# all copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+# THE SOFTWARE.
+#
+
+# This workflow will build a Java project with Maven
+# For more information see: https://help.github.com/actions/language-and-framework-guides/building-and-testing-java-with-maven
+
+name: Java PR Builder
+
+on:
+  pull_request:
+    branches: [ master ]
+    types: [ opened, reopened, synchronize ]
+
+jobs:
+  build:
+
+    name: Build JDP
+    runs-on: ubuntu-20.04
+    strategy:
+      matrix:
+        java-version: [ 11.0.3, 11 ]
+    steps:
+    
+    - name: Checkout Code
+      uses: actions/checkout@v2
+    
+    - name: Set up JDK ${{ matrix.java-version }}
+      uses: actions/setup-java@v2
+      with:
+        java-version: ${{ matrix.java-version }}
+        distribution: 'zulu'
+        cache: 'maven'
+    
+    # Some tests need screen access
+    - name: Install xvfb
+      run: sudo apt-get install -y xvfb
+    
+    - name: Build with Maven
+      run: xvfb-run ./mvnw clean verify

.gitignore

@@ -1,19 +1,55 @@
+################## Eclipse ######################
 target
 .metadata
 .settings
 .classpath
 .project
 *.class
-# Package Files #
+tmp/
+*.tmp
+*.bak
+*~.nib
+local.properties
+.loadpath
+.recommenders
+.DS_Store
+
+#######  Java annotation processor (APT) ########
+.factorypath
+
+################ Package Files ##################
 *.jar
 *.war
 *.ear
-.idea
-*.iml
 *.swp
 datanucleus.log
 /bin/
-/bin/
-/bin/
 *.log
 event-sourcing/Journal.json
+
+################## Checkstyle ###################
+.checkstyle
+
+##################### STS #######################
+.apt_generated
+.springBeans
+.sts4-cache
+
+################# IntelliJ IDEA #################
+.idea
+*.iws
+*.iml
+*.ipr
+
+################### NetBeans ####################
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+build/
+!**/src/main/**/build/
+!**/src/test/**/build/
+
+#################### VS Code ####################
+.vscode/

.mvn/wrapper/MavenWrapperDownloader.java

@@ -0,0 +1,125 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2021 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+import java.net.*;
+import java.io.*;
+import java.nio.channels.*;
+import java.util.Properties;
+
+public class MavenWrapperDownloader {
+
+    private static final String WRAPPER_VERSION = "0.5.6";
+    /**
+     * Default URL to download the maven-wrapper.jar from, if no 'downloadUrl' is provided.
+     */
+    private static final String DEFAULT_DOWNLOAD_URL = "https://repo.maven.apache.org/maven2/io/takari/maven-wrapper/"
+        + WRAPPER_VERSION + "/maven-wrapper-" + WRAPPER_VERSION + ".jar";
+
+    /**
+     * Path to the maven-wrapper.properties file, which might contain a downloadUrl property to
+     * use instead of the default one.
+     */
+    private static final String MAVEN_WRAPPER_PROPERTIES_PATH =
+            ".mvn/wrapper/maven-wrapper.properties";
+
+    /**
+     * Path where the maven-wrapper.jar will be saved to.
+     */
+    private static final String MAVEN_WRAPPER_JAR_PATH =
+            ".mvn/wrapper/maven-wrapper.jar";
+
+    /**
+     * Name of the property which should be used to override the default download url for the wrapper.
+     */
+    private static final String PROPERTY_NAME_WRAPPER_URL = "wrapperUrl";
+
+    public static void main(String args[]) {
+        System.out.println("- Downloader started");
+        File baseDirectory = new File(args[0]);
+        System.out.println("- Using base directory: " + baseDirectory.getAbsolutePath());
+
+        // If the maven-wrapper.properties exists, read it and check if it contains a custom
+        // wrapperUrl parameter.
+        File mavenWrapperPropertyFile = new File(baseDirectory, MAVEN_WRAPPER_PROPERTIES_PATH);
+        String url = DEFAULT_DOWNLOAD_URL;
+        if(mavenWrapperPropertyFile.exists()) {
+            FileInputStream mavenWrapperPropertyFileInputStream = null;
+            try {
+                mavenWrapperPropertyFileInputStream = new FileInputStream(mavenWrapperPropertyFile);
+                Properties mavenWrapperProperties = new Properties();
+                mavenWrapperProperties.load(mavenWrapperPropertyFileInputStream);
+                url = mavenWrapperProperties.getProperty(PROPERTY_NAME_WRAPPER_URL, url);
+            } catch (IOException e) {
+                System.out.println("- ERROR loading '" + MAVEN_WRAPPER_PROPERTIES_PATH + "'");
+            } finally {
+                try {
+                    if(mavenWrapperPropertyFileInputStream != null) {
+                        mavenWrapperPropertyFileInputStream.close();
+                    }
+                } catch (IOException e) {
+                    // Ignore ...
+                }
+            }
+        }
+        System.out.println("- Downloading from: " + url);
+
+        File outputFile = new File(baseDirectory.getAbsolutePath(), MAVEN_WRAPPER_JAR_PATH);
+        if(!outputFile.getParentFile().exists()) {
+            if(!outputFile.getParentFile().mkdirs()) {
+                System.out.println(
+                        "- ERROR creating output directory '" + outputFile.getParentFile().getAbsolutePath() + "'");
+            }
+        }
+        System.out.println("- Downloading to: " + outputFile.getAbsolutePath());
+        try {
+            downloadFileFromURL(url, outputFile);
+            System.out.println("Done");
+            System.exit(0);
+        } catch (Throwable e) {
+            System.out.println("- Error downloading");
+            e.printStackTrace();
+            System.exit(1);
+        }
+    }
+
+    private static void downloadFileFromURL(String urlString, File destination) throws Exception {
+        if (System.getenv("MVNW_USERNAME") != null && System.getenv("MVNW_PASSWORD") != null) {
+            String username = System.getenv("MVNW_USERNAME");
+            char[] password = System.getenv("MVNW_PASSWORD").toCharArray();
+            Authenticator.setDefault(new Authenticator() {
+                @Override
+                protected PasswordAuthentication getPasswordAuthentication() {
+                    return new PasswordAuthentication(username, password);
+                }
+            });
+        }
+        URL website = new URL(urlString);
+        ReadableByteChannel rbc;
+        rbc = Channels.newChannel(website.openStream());
+        FileOutputStream fos = new FileOutputStream(destination);
+        fos.getChannel().transferFrom(rbc, 0, Long.MAX_VALUE);
+        fos.close();
+        rbc.close();
+    }
+
+}

.mvn/wrapper/maven-wrapper.properties

@@ -0,0 +1,18 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+# 
+#   http://www.apache.org/licenses/LICENSE-2.0
+# 
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+distributionUrl=https://repo.maven.apache.org/maven2/org/apache/maven/apache-maven/3.8.4/apache-maven-3.8.4-bin.zip
+wrapperUrl=https://repo.maven.apache.org/maven2/org/apache/maven/wrapper/maven-wrapper/3.1.0/maven-wrapper-3.1.0.jar

.travis.yml

@@ -1,36 +0,0 @@
-language: java
-dist: bionic
-jdk:
-- openjdk11
-sudo: required
-
-env:
-  global:
-  - secure: "DCpazS3nkLnter3sguXEAS2fC/1ZWNfM+XLyif9MfNFxlZdpni2vCD/jA0Rdpga8puQWHNVLyAec+RPFH/2qSmJ1c1UTV5MaLv8tPqwUX0VFA+1I6XoSv6oX4ldHTBWHEWqQHkRFOLoil0h0edc0tTOWQwXF8U+DLAB+HkRb4gw="
-
-services:
-- xvfb
-
-addons:
-  sonarcloud:
-    organization: "iluwatar"
-    token:
-      secure: "FpHwMYPMkdWU6CeIB7+O3qIeIM4vJMp47UjkKK53f0w0s6tPZofZZkab+gcL2TqKSil7sFVB/AQXU1cUubflRszwcLbNsc8H2yFehD79o0o0Mqd1Dd5ip/q0KQbHkkln+InFlVLfvrLB4Xd4mlQVxbGhqpULBhXjKzFzQlRFcuU="
-script:
-  # Because of Travis security restrictions, SonarCloud analysis cannot be run on pull requests originated from forks
-  # See https://docs.travis-ci.com/user/pull-requests/#pull-requests-and-security-restrictions
-  - 'if [ "$TRAVIS_PULL_REQUEST" != "false" ]; then mvn clean verify; fi'
-  - 'if [ "$TRAVIS_PULL_REQUEST" = "false" ]; then mvn clean verify sonar:sonar -Dsonar.projectKey=iluwatar_java-design-patterns -Dsonar.host.url=https://sonarcloud.io; fi'
-
-after_success:
-- bash update-website.sh
-
-notifications:
-  email:
-    - iluwatar@gmail.com
-  webhooks:
-    urls:
-      - https://webhooks.gitter.im/e/3319623945358a093a6f
-    on_success: change  # options: [always|never|change] default: always
-    on_failure: always  # options: [always|never|change] default: always
-    on_start: never     # options: [always|never|change] default: always

LICENSE.md

@@ -1,6 +1,6 @@
 The MIT License (MIT)
 
-Copyright (c) 2014-2016 Ilkka Seppälä
+Copyright <EFBFBD> 2014-2021 Ilkka Sepp<EFBFBD>l<EFBFBD>
 
 Permission is hereby granted, free of charge, to any person obtaining a copy
 of this software and associated documentation files (the "Software"), to deal
@@ -19,3 +19,6 @@ AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
+
+Module Model-view-viewmodel is using ZK framework
+ZK framework is licensed under LGPL and the license can be found at lgpl-3.0.txt

README.md

@@ -4,14 +4,24 @@
 
 # Design patterns implemented in Java
 
-[![Build status](https://travis-ci.org/iluwatar/java-design-patterns.svg?branch=master)](https://travis-ci.org/iluwatar/java-design-patterns)
+![Java CI](https://github.com/iluwatar/java-design-patterns/workflows/Java%20CI/badge.svg)
 [![License MIT](https://img.shields.io/badge/license-MIT-blue.svg)](https://raw.githubusercontent.com/iluwatar/java-design-patterns/master/LICENSE.md)
+[![Lines of Code](https://sonarcloud.io/api/project_badges/measure?project=iluwatar_java-design-patterns&metric=ncloc)](https://sonarcloud.io/dashboard?id=iluwatar_java-design-patterns)
+[![Coverage](https://sonarcloud.io/api/project_badges/measure?project=iluwatar_java-design-patterns&metric=coverage)](https://sonarcloud.io/dashboard?id=iluwatar_java-design-patterns)
 [![Join the chat at https://gitter.im/iluwatar/java-design-patterns](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/iluwatar/java-design-patterns?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
-[![Sonarcloud Status](https://sonarcloud.io/api/project_badges/measure?project=iluwatar_java-design-patterns&metric=alert_status)](https://sonarcloud.io/dashboard?id=iluwatar_java-design-patterns) 
+<!-- ALL-CONTRIBUTORS-BADGE:START - Do not remove or modify this section -->
+[![All Contributors](https://img.shields.io/badge/all_contributors-198-orange.svg?style=flat-square)](#contributors-)
+<!-- ALL-CONTRIBUTORS-BADGE:END -->
+
+<br/>
+
+Read in different language : [**zh**](localization/zh/README.md), [**ko**](localization/ko/README.md), [**fr**](localization/fr/README.md), [**tr**](localization/tr/README.md), [**ar**](localization/ar/README.md), [**es**](localization/es/README.md), [**pt**](localization/pt/README.md), [**id**](localization/id/README.md), [**ru**](localization/ru/README.md), [**de**](localization/de/README.md), [**ja**](localization/ja/README.md)
+
+<br/>
 
 # Introduction
 
-Design patterns are the best formalized practices a programmer can use to
+Design patterns are the best, formalized practices a programmer can use to
 solve common problems when designing an application or system.
 
 Design patterns can speed up the development process by providing tested, proven
@@ -24,36 +34,306 @@ are familiar with the patterns.
 # Getting started
 
 This site showcases Java Design Patterns. The solutions have been developed by
-experienced programmers and architects from the open source community. The 
-patterns can be browsed by their high level descriptions or by looking at their
-source code. The source code examples are well commented and can be thought as
-programming tutorials how to implement a specific pattern. We use the most
-popular battle-proven open source Java technologies.
+experienced programmers and architects from the open-source community. The
+patterns can be browsed by their high-level descriptions or by looking at their
+source code. The source code examples are well commented and can be thought of as
+programming tutorials on how to implement a specific pattern. We use the most
+popular battle-proven open-source Java technologies.
 
 Before you dive into the material, you should be familiar with various
-software design principles.
+[Software Design Principles](https://java-design-patterns.com/principles/).
 
 All designs should be as simple as possible. You should start with KISS, YAGNI,
 and Do The Simplest Thing That Could Possibly Work principles. Complexity and
 patterns should only be introduced when they are needed for practical
 extensibility.
 
-Once you are familiar with these concepts you can start drilling down into
-patterns by any of the following approaches
+Once you are familiar with these concepts you can start drilling down into the
+[available design patterns](https://java-design-patterns.com/patterns/) by any
+of the following approaches
 
- - Using difficulty tags, `Difficulty-Beginner`, `Difficulty-Intermediate` & `Difficulty-Expert`.
+ - Search for a specific pattern by name. Can't find one? Please report a new pattern [here](https://github.com/iluwatar/java-design-patterns/issues).
+ - Using tags such as `Performance`, `Gang of Four` or `Data access`.
  - Using pattern categories, `Creational`, `Behavioral`, and others.
- - Search for a specific pattern. Can't find one? Please report a new pattern [here](https://github.com/iluwatar/java-design-patterns/issues).
 
-Hopefully you find the object oriented solutions presented on this site useful
-in your architectures and have as much fun learning them as we had developing them.
+Hopefully, you find the object-oriented solutions presented on this site useful
+in your architectures and have as much fun learning them as we had while developing them.
 
 # How to contribute
 
-If you are willing to contribute to the project you will find the relevant information in 
-our [developer wiki](https://github.com/iluwatar/java-design-patterns/wiki). We will help 
+If you are willing to contribute to the project you will find the relevant information in
+our [developer wiki](https://github.com/iluwatar/java-design-patterns/wiki). We will help
 you and answer your questions in the [Gitter chatroom](https://gitter.im/iluwatar/java-design-patterns).
 
 # License
 
 This project is licensed under the terms of the MIT license.
+
+# Contributors
+
+<!-- ALL-CONTRIBUTORS-LIST:START - Do not remove or modify this section -->
+<!-- prettier-ignore-start -->
+<!-- markdownlint-disable -->
+<table>
+  <tr>
+    <td align="center"><a href="https://github.com/iluwatar"><img src="https://avatars1.githubusercontent.com/u/582346?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Ilkka Seppälä</b></sub></a><br /><a href="#projectManagement-iluwatar" title="Project Management">📆</a> <a href="#maintenance-iluwatar" title="Maintenance">🚧</a> <a href="#content-iluwatar" title="Content">🖋</a></td>
+    <td align="center"><a href="http://subho.xyz"><img src="https://avatars0.githubusercontent.com/u/13291222?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Subhrodip Mohanta</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=ohbus" title="Code">💻</a> <a href="https://github.com/iluwatar/java-design-patterns/pulls?q=is%3Apr+reviewed-by%3Aohbus" title="Reviewed Pull Requests">👀</a> <a href="#maintenance-ohbus" title="Maintenance">🚧</a></td>
+    <td align="center"><a href="https://github.com/amit1307"><img src="https://avatars0.githubusercontent.com/u/23420222?v=4?s=100" width="100px;" alt=""/><br /><sub><b>amit1307</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=amit1307" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/npathai"><img src="https://avatars2.githubusercontent.com/u/1792515?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Narendra Pathai</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=npathai" title="Code">💻</a> <a href="#ideas-npathai" title="Ideas, Planning, & Feedback">🤔</a> <a href="https://github.com/iluwatar/java-design-patterns/pulls?q=is%3Apr+reviewed-by%3Anpathai" title="Reviewed Pull Requests">👀</a></td>
+    <td align="center"><a href="https://github.com/fluxw42"><img src="https://avatars1.githubusercontent.com/u/1545460?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Jeroen Meulemeester</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=fluxw42" title="Code">💻</a></td>
+    <td align="center"><a href="http://www.joemccarthy.co.uk"><img src="https://avatars0.githubusercontent.com/u/4526195?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Joseph McCarthy</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=mikulucky" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/thomasoss"><img src="https://avatars1.githubusercontent.com/u/22516154?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Thomas</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=thomasoss" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/anuragagarwal561994"><img src="https://avatars1.githubusercontent.com/u/6075379?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Anurag Agarwal</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=anuragagarwal561994" title="Code">💻</a></td>
+    <td align="center"><a href="https://markusmo3.github.io"><img src="https://avatars1.githubusercontent.com/u/3317416?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Markus Moser</b></sub></a><br /><a href="#design-markusmo3" title="Design">🎨</a> <a href="https://github.com/iluwatar/java-design-patterns/commits?author=markusmo3" title="Code">💻</a> <a href="#ideas-markusmo3" title="Ideas, Planning, & Feedback">🤔</a></td>
+    <td align="center"><a href="https://twitter.com/i_sabiq"><img src="https://avatars1.githubusercontent.com/u/19510920?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Sabiq Ihab</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=isabiq" title="Code">💻</a></td>
+    <td align="center"><a href="http://inbravo.github.io"><img src="https://avatars3.githubusercontent.com/u/5253764?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Amit Dixit</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=inbravo" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/piyushchaudhari04"><img src="https://avatars3.githubusercontent.com/u/10268029?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Piyush Kailash Chaudhari</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=piyushchaudhari04" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/joshzambales"><img src="https://avatars1.githubusercontent.com/u/8704552?v=4?s=100" width="100px;" alt=""/><br /><sub><b>joshzambales</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=joshzambales" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/Crossy147"><img src="https://avatars2.githubusercontent.com/u/7272996?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Kamil Pietruszka</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Crossy147" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="http://cs.joensuu.fi/~zkhayda"><img src="https://avatars2.githubusercontent.com/u/660742?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Zafar Khaydarov</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=zafarella" title="Code">💻</a> <a href="https://github.com/iluwatar/java-design-patterns/commits?author=zafarella" title="Documentation">📖</a></td>
+    <td align="center"><a href="https://kemitix.github.io/"><img src="https://avatars1.githubusercontent.com/u/1147749?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Paul Campbell</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=kemitix" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/Argyro-Sioziou"><img src="https://avatars0.githubusercontent.com/u/22822639?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Argyro Sioziou</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Argyro-Sioziou" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/TylerMcConville"><img src="https://avatars0.githubusercontent.com/u/4946449?v=4?s=100" width="100px;" alt=""/><br /><sub><b>TylerMcConville</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=TylerMcConville" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/saksham93"><img src="https://avatars1.githubusercontent.com/u/37399540?v=4?s=100" width="100px;" alt=""/><br /><sub><b>saksham93</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=saksham93" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/nikhilbarar"><img src="https://avatars2.githubusercontent.com/u/37332144?v=4?s=100" width="100px;" alt=""/><br /><sub><b>nikhilbarar</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=nikhilbarar" title="Code">💻</a></td>
+    <td align="center"><a href="http://colinbut.com"><img src="https://avatars2.githubusercontent.com/u/10725674?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Colin But</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=colinbut" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/ruslanpa"><img src="https://avatars2.githubusercontent.com/u/1503411?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Ruslan</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=ruslanpa" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/JuhoKang"><img src="https://avatars1.githubusercontent.com/u/4745294?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Juho Kang</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=JuhoKang" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/dheeraj-mummareddy"><img src="https://avatars2.githubusercontent.com/u/7002230?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Dheeraj Mummareddy</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=dheeraj-mummareddy" title="Code">💻</a></td>
+    <td align="center"><a href="https://www.bernardosulzbach.com"><img src="https://avatars0.githubusercontent.com/u/8271090?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Bernardo Sulzbach</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=bernardosulzbach" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/4lexis"><img src="https://avatars0.githubusercontent.com/u/19871727?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Aleksandar Dudukovic</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=4lexis" title="Code">💻</a></td>
+    <td align="center"><a href="https://www.yusufaytas.com"><img src="https://avatars2.githubusercontent.com/u/1049483?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Yusuf Aytaş</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=yusufaytas" title="Code">💻</a></td>
+    <td align="center"><a href="http://futurehomes.hu"><img src="https://avatars2.githubusercontent.com/u/1001491?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Mihály Kuprivecz</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=qpi" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/kapinuss"><img src="https://avatars0.githubusercontent.com/u/17639945?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Stanislav Kapinus</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=kapinuss" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/gvsharma"><img src="https://avatars1.githubusercontent.com/u/6648152?v=4?s=100" width="100px;" alt=""/><br /><sub><b>GVSharma</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=gvsharma" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/SrdjanPaunovic"><img src="https://avatars1.githubusercontent.com/u/22815104?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Srđan Paunović</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=SrdjanPaunovic" title="Code">💻</a></td>
+    <td align="center"><a href="https://sideris.xyz/"><img src="https://avatars3.githubusercontent.com/u/5484694?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Petros G. Sideris</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=sideris" title="Code">💻</a></td>
+    <td align="center"><a href="https://www.linkedin.com/in/pramodgupta3/"><img src="https://avatars1.githubusercontent.com/u/2184241?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Pramod Gupta</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/pulls?q=is%3Apr+reviewed-by%3AIAmPramod" title="Reviewed Pull Requests">👀</a></td>
+    <td align="center"><a href="https://amarnath510.github.io/portfolio"><img src="https://avatars0.githubusercontent.com/u/4599623?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Amarnath Chandana</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Amarnath510" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/Anurag870"><img src="https://avatars1.githubusercontent.com/u/6295975?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Anurag870</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Anurag870" title="Code">💻</a> <a href="https://github.com/iluwatar/java-design-patterns/commits?author=Anurag870" title="Documentation">📖</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="http://theerroris.me"><img src="https://avatars0.githubusercontent.com/u/1685953?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Wes Gilleland</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Deathnerd" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/Harshrajsinh"><img src="https://avatars2.githubusercontent.com/u/22811531?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Harshraj Thakor</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Harshrajsinh" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/MaVdbussche"><img src="https://avatars1.githubusercontent.com/u/26136934?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Martin Vandenbussche</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=MaVdbussche" title="Code">💻</a></td>
+    <td align="center"><a href="https://alexsomai.com"><img src="https://avatars1.githubusercontent.com/u/5720977?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Alexandru Somai</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=alexsomai" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/amogozov"><img src="https://avatars3.githubusercontent.com/u/7372215?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Artur Mogozov</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=amogozov" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/anthonycampbell"><img src="https://avatars3.githubusercontent.com/u/10249255?v=4?s=100" width="100px;" alt=""/><br /><sub><b>anthony</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=anthonycampbell" title="Code">💻</a></td>
+    <td align="center"><a href="http://ccygnus.com/"><img src="https://avatars1.githubusercontent.com/u/9342724?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Christian Cygnus</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=christophercolumbusdog" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://about.me/dzmitryh"><img src="https://avatars2.githubusercontent.com/u/5390492?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Dima Gubin</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=dzmitryh" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/jjjimenez100"><img src="https://avatars3.githubusercontent.com/u/22243493?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Joshua Jimenez</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=jjjimenez100" title="Code">💻</a></td>
+    <td align="center"><a href="http://about.me/kaiwinter"><img src="https://avatars0.githubusercontent.com/u/110982?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Kai Winter</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=kaiwinter" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/lbroman"><img src="https://avatars1.githubusercontent.com/u/86007?v=4?s=100" width="100px;" alt=""/><br /><sub><b>lbroman</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=lbroman" title="Code">💻</a></td>
+    <td align="center"><a href="https://przemeknowak.com"><img src="https://avatars1.githubusercontent.com/u/3254609?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Przemek</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=pnowy" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/prafful1"><img src="https://avatars0.githubusercontent.com/u/14350274?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Prafful Agarwal</b></sub></a><br /><a href="#content-prafful1" title="Content">🖋</a></td>
+    <td align="center"><a href="https://github.com/sankypanhale"><img src="https://avatars1.githubusercontent.com/u/6478783?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Sanket Panhale</b></sub></a><br /><a href="#content-sankypanhale" title="Content">🖋</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/staillebois"><img src="https://avatars0.githubusercontent.com/u/23701200?v=4?s=100" width="100px;" alt=""/><br /><sub><b>staillebois</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=staillebois" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/valdar-hu"><img src="https://avatars3.githubusercontent.com/u/17962817?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Krisztián Nagy</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=valdar-hu" title="Code">💻</a></td>
+    <td align="center"><a href="https://www.vanogrid.com"><img src="https://avatars0.githubusercontent.com/u/4307918?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Alexander Ivanov</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=vanogrid" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/yosfik"><img src="https://avatars3.githubusercontent.com/u/4850270?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Yosfik Alqadri</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=yosfik" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/7agustibm"><img src="https://avatars0.githubusercontent.com/u/8149332?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Agustí Becerra Milà</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=7agustibm" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/Juaanma"><img src="https://avatars3.githubusercontent.com/u/7390500?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Juan Manuel Suárez</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Juaanma" title="Code">💻</a></td>
+    <td align="center"><a href="http://www.devsedge.net/"><img src="https://avatars0.githubusercontent.com/u/9956006?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Luigi Cortese</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=LuigiCortese" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/Rzeposlaw"><img src="https://avatars2.githubusercontent.com/u/18425745?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Katarzyna Rzepecka</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Rzeposlaw" title="Code">💻</a></td>
+    <td align="center"><a href="http://adamski.pro"><img src="https://avatars1.githubusercontent.com/u/6537430?v=4?s=100" width="100px;" alt=""/><br /><sub><b>adamski.pro</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=akrystian" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/baislsl"><img src="https://avatars0.githubusercontent.com/u/17060584?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Shengli Bai</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=baislsl" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/besok"><img src="https://avatars2.githubusercontent.com/u/29834592?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Boris</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=besok" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/dmitraver"><img src="https://avatars3.githubusercontent.com/u/1798156?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Dmitry Avershin</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=dmitraver" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/fanofxiaofeng"><img src="https://avatars0.githubusercontent.com/u/3983683?v=4?s=100" width="100px;" alt=""/><br /><sub><b>靳阳</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=fanofxiaofeng" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/hoangnam2261"><img src="https://avatars2.githubusercontent.com/u/31692990?v=4?s=100" width="100px;" alt=""/><br /><sub><b>hoangnam2261</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=hoangnam2261" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/jarpit96"><img src="https://avatars2.githubusercontent.com/u/10098713?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Arpit Jain</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=jarpit96" title="Code">💻</a></td>
+    <td align="center"><a href="http://joningi.net"><img src="https://avatars2.githubusercontent.com/u/6115148?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Jón Ingi Sveinbjörnsson</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=joningiwork" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/kirill-vlasov"><img src="https://avatars3.githubusercontent.com/u/16112495?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Kirill Vlasov</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=kirill-vlasov" title="Code">💻</a></td>
+    <td align="center"><a href="http://mitchell-irvin.com"><img src="https://avatars0.githubusercontent.com/u/16233245?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Mitchell Irvin</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=mitchellirvin" title="Code">💻</a></td>
+    <td align="center"><a href="https://ranjeet-floyd.github.io"><img src="https://avatars0.githubusercontent.com/u/1992972?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Ranjeet</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=ranjeet-floyd" title="Code">💻</a></td>
+    <td align="center"><a href="https://alwayswithme.github.io"><img src="https://avatars3.githubusercontent.com/u/3234786?v=4?s=100" width="100px;" alt=""/><br /><sub><b>PhoenixYip</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Alwayswithme" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/MSaifAsif"><img src="https://avatars1.githubusercontent.com/u/6280554?v=4?s=100" width="100px;" alt=""/><br /><sub><b>M Saif Asif</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=MSaifAsif" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/kanwarpreet25"><img src="https://avatars0.githubusercontent.com/u/39183641?v=4?s=100" width="100px;" alt=""/><br /><sub><b>kanwarpreet25</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=kanwarpreet25" title="Code">💻</a></td>
+    <td align="center"><a href="http://leonmak.me"><img src="https://avatars3.githubusercontent.com/u/13071508?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Leon Mak</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=leonmak" title="Code">💻</a></td>
+    <td align="center"><a href="http://www.wramdemark.se"><img src="https://avatars2.githubusercontent.com/u/7052193?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Per Wramdemark</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=perwramdemark" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/waisuan"><img src="https://avatars2.githubusercontent.com/u/10975700?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Evan Sia Wai Suan</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=waisuan" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/AnaghaSasikumar"><img src="https://avatars2.githubusercontent.com/u/42939261?v=4?s=100" width="100px;" alt=""/><br /><sub><b>AnaghaSasikumar</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=AnaghaSasikumar" title="Code">💻</a></td>
+    <td align="center"><a href="https://christofferh.com"><img src="https://avatars1.githubusercontent.com/u/767643?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Christoffer Hamberg</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=christofferh" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/dgruntz"><img src="https://avatars0.githubusercontent.com/u/1516800?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Dominik Gruntz</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=dgruntz" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://bitbucket.org/hannespernpeintner/"><img src="https://avatars3.githubusercontent.com/u/1679437?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Hannes</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=hannespernpeintner" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/leogtzr"><img src="https://avatars0.githubusercontent.com/u/1211969?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Leo Gutiérrez Ramírez</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=leogtzr" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/npczwh"><img src="https://avatars0.githubusercontent.com/u/14066422?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Zhang WH</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=npczwh" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/oconnelc"><img src="https://avatars0.githubusercontent.com/u/1112973?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Christopher O'Connell</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=oconnelc" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/giorgosmav21"><img src="https://avatars2.githubusercontent.com/u/22855493?v=4?s=100" width="100px;" alt=""/><br /><sub><b>George Mavroeidis</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=giorgosmav21" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/hbothra15"><img src="https://avatars1.githubusercontent.com/u/7418012?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Hemant Bothra</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=hbothra15" title="Code">💻</a> <a href="#design-hbothra15" title="Design">🎨</a></td>
+    <td align="center"><a href="https://www.kevinpeters.net/about/"><img src="https://avatars1.githubusercontent.com/u/12736734?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Kevin Peters</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=igeligel" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://llorllale.github.io/"><img src="https://avatars1.githubusercontent.com/u/2019896?v=4?s=100" width="100px;" alt=""/><br /><sub><b>George Aristy</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=llorllale" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/mookkiah"><img src="https://avatars1.githubusercontent.com/u/8975264?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Mahendran Mookkiah</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=mookkiah" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/Azureyjt"><img src="https://avatars2.githubusercontent.com/u/18476317?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Azureyjt</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Azureyjt" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/vehpsr"><img src="https://avatars2.githubusercontent.com/u/3133265?v=4?s=100" width="100px;" alt=""/><br /><sub><b>gans</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=vehpsr" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/ThatGuyWithTheHat"><img src="https://avatars0.githubusercontent.com/u/24470582?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Matt</b></sub></a><br /><a href="#content-ThatGuyWithTheHat" title="Content">🖋</a></td>
+    <td align="center"><a href="https://www.linkedin.com/in/gopinathlangote/"><img src="https://avatars2.githubusercontent.com/u/10210778?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Gopinath Langote</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=gopinath-langote" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/hoswey"><img src="https://avatars3.githubusercontent.com/u/3689445?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Hoswey</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=hoswey" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/amit2103"><img src="https://avatars3.githubusercontent.com/u/7566692?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Amit Pandey</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=amit2103" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/gwildor28"><img src="https://avatars0.githubusercontent.com/u/16000365?v=4?s=100" width="100px;" alt=""/><br /><sub><b>gwildor28</b></sub></a><br /><a href="#content-gwildor28" title="Content">🖋</a></td>
+    <td align="center"><a href="https://t.me/paul_docker"><img src="https://avatars1.githubusercontent.com/u/2404785?v=4?s=100" width="100px;" alt=""/><br /><sub><b>田浩</b></sub></a><br /><a href="#content-llitfkitfk" title="Content">🖋</a></td>
+    <td align="center"><a href="https://twitter.com/StPitsios"><img src="https://avatars1.githubusercontent.com/u/6773603?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Stamatis Pitsios</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=pitsios-s" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/qza"><img src="https://avatars3.githubusercontent.com/u/233149?v=4?s=100" width="100px;" alt=""/><br /><sub><b>qza</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=qza" title="Code">💻</a></td>
+    <td align="center"><a href="http://tschis.github.io"><img src="https://avatars1.githubusercontent.com/u/20662669?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Rodolfo Forte</b></sub></a><br /><a href="#content-Tschis" title="Content">🖋</a></td>
+    <td align="center"><a href="https://github.com/ankurkaushal"><img src="https://avatars2.githubusercontent.com/u/2236616?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Ankur Kaushal</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=ankurkaushal" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://www.linkedin.com/in/ovidijus-okinskas/"><img src="https://avatars0.githubusercontent.com/u/20372387?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Ovidijus Okinskas</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=okinskas" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/robertt240"><img src="https://avatars1.githubusercontent.com/u/9137432?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Robert Kasperczyk</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=robertt240" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/trautonen"><img src="https://avatars3.githubusercontent.com/u/1641063?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Tapio Rautonen</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=trautonen" title="Code">💻</a></td>
+    <td align="center"><a href="http://vk.com/yuri.orlov"><img src="https://avatars0.githubusercontent.com/u/1595733?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Yuri Orlov</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=yorlov" title="Code">💻</a></td>
+    <td align="center"><a href="https://www.linkedin.com/in/varunu28/"><img src="https://avatars0.githubusercontent.com/u/7676016?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Varun Upadhyay</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=varunu28" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/PalAditya"><img src="https://avatars2.githubusercontent.com/u/25523604?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Aditya Pal</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=PalAditya" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/grzesiekkedzior"><img src="https://avatars3.githubusercontent.com/u/23739158?v=4?s=100" width="100px;" alt=""/><br /><sub><b>grzesiekkedzior</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=grzesiekkedzior" title="Code">💻</a> <a href="https://github.com/iluwatar/java-design-patterns/pulls?q=is%3Apr+reviewed-by%3Agrzesiekkedzior" title="Reviewed Pull Requests">👀</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/sivasubramanim"><img src="https://avatars2.githubusercontent.com/u/51107434?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Sivasubramani M</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=sivasubramanim" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/d4gg4d"><img src="https://avatars2.githubusercontent.com/u/99457?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Sami Airaksinen</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=d4gg4d" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/vertti"><img src="https://avatars0.githubusercontent.com/u/557751?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Janne Sinivirta</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=vertti" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/Bobo1239"><img src="https://avatars1.githubusercontent.com/u/2302947?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Boris-Chengbiao Zhou</b></sub></a><br /><a href="#content-Bobo1239" title="Content">🖋</a></td>
+    <td align="center"><a href="https://jahhein.github.io"><img src="https://avatars2.githubusercontent.com/u/10779515?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Jacob Hein</b></sub></a><br /><a href="#content-Jahhein" title="Content">🖋</a></td>
+    <td align="center"><a href="https://github.com/iamrichardjones"><img src="https://avatars3.githubusercontent.com/u/14842151?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Richard Jones</b></sub></a><br /><a href="#content-iamrichardjones" title="Content">🖋</a></td>
+    <td align="center"><a href="https://rachelcarmena.github.io"><img src="https://avatars0.githubusercontent.com/u/22792183?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Rachel M. Carmena</b></sub></a><br /><a href="#content-rachelcarmena" title="Content">🖋</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://zd-zero.github.io"><img src="https://avatars0.githubusercontent.com/u/21978370?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Zaerald Denze Lungos</b></sub></a><br /><a href="#content-zd-zero" title="Content">🖋</a></td>
+    <td align="center"><a href="https://webpro.nl"><img src="https://avatars1.githubusercontent.com/u/456426?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Lars Kappert</b></sub></a><br /><a href="#content-webpro" title="Content">🖋</a></td>
+    <td align="center"><a href="https://xiaod.info"><img src="https://avatars2.githubusercontent.com/u/21277644?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Mike Liu</b></sub></a><br /><a href="#translation-xiaod-dev" title="Translation">🌍</a></td>
+    <td align="center"><a href="https://github.com/charlesfinley"><img src="https://avatars1.githubusercontent.com/u/6307904?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Matt Dolan</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=charlesfinley" title="Code">💻</a> <a href="https://github.com/iluwatar/java-design-patterns/pulls?q=is%3Apr+reviewed-by%3Acharlesfinley" title="Reviewed Pull Requests">👀</a></td>
+    <td align="center"><a href="https://github.com/MananS77"><img src="https://avatars3.githubusercontent.com/u/21033516?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Manan</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/pulls?q=is%3Apr+reviewed-by%3AMananS77" title="Reviewed Pull Requests">👀</a></td>
+    <td align="center"><a href="https://github.com/nishant"><img src="https://avatars2.githubusercontent.com/u/15331971?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Nishant Arora</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=nishant" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/raja-peeyush-kumar-singh"><img src="https://avatars0.githubusercontent.com/u/5496024?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Peeyush</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=raja-peeyush-kumar-singh" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/ravening"><img src="https://avatars1.githubusercontent.com/u/10645273?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Rakesh</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=ravening" title="Code">💻</a> <a href="https://github.com/iluwatar/java-design-patterns/pulls?q=is%3Apr+reviewed-by%3Aravening" title="Reviewed Pull Requests">👀</a></td>
+    <td align="center"><a href="https://github.com/vINCENT8888801"><img src="https://avatars0.githubusercontent.com/u/8037883?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Wei Seng</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=vINCENT8888801" title="Code">💻</a></td>
+    <td align="center"><a href="https://www.linkedin.com/in/ashish-trivedi-218379135/"><img src="https://avatars3.githubusercontent.com/u/23194128?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Ashish Trivedi</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=ashishtrivedi16" title="Code">💻</a></td>
+    <td align="center"><a href="https://rayyounghong.com"><img src="https://avatars1.githubusercontent.com/u/41055099?v=4?s=100" width="100px;" alt=""/><br /><sub><b>洪月阳</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=RayYH" title="Code">💻</a></td>
+    <td align="center"><a href="https://xdvrx1.github.io/"><img src="https://avatars0.githubusercontent.com/u/47092464?v=4?s=100" width="100px;" alt=""/><br /><sub><b>xdvrx1</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/pulls?q=is%3Apr+reviewed-by%3Axdvrx1" title="Reviewed Pull Requests">👀</a> <a href="#ideas-xdvrx1" title="Ideas, Planning, & Feedback">🤔</a></td>
+    <td align="center"><a href="https://github.com/nahteb"><img src="https://avatars3.githubusercontent.com/u/13121570?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Bethan Palmer</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=nahteb" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/ToxicDreamz"><img src="https://avatars0.githubusercontent.com/u/45225562?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Toxic Dreamz</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=ToxicDreamz" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="http://www.edycutjong.com"><img src="https://avatars1.githubusercontent.com/u/1098102?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Edy Cu Tjong</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=edycutjong" title="Documentation">📖</a></td>
+    <td align="center"><a href="https://github.com/mkrzywanski"><img src="https://avatars0.githubusercontent.com/u/15279585?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Michał Krzywański</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=mkrzywanski" title="Code">💻</a></td>
+    <td align="center"><a href="https://www.stefan-birkner.de"><img src="https://avatars1.githubusercontent.com/u/711349?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Stefan Birkner</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=stefanbirkner" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/fedorskvorcov"><img src="https://avatars3.githubusercontent.com/u/43882212?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Fedor Skvorcov</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=fedorskvorcov" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/samilAyoub"><img src="https://avatars0.githubusercontent.com/u/61546990?v=4?s=100" width="100px;" alt=""/><br /><sub><b>samilAyoub</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=samilAyoub" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/vdlald"><img src="https://avatars0.githubusercontent.com/u/29997701?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Vladislav Golubinov</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=vdlald" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/swarajsaaj"><img src="https://avatars2.githubusercontent.com/u/6285049?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Swaraj</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=swarajsaaj" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="http://christophflick.de"><img src="https://avatars0.githubusercontent.com/u/4465376?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Christoph Flick</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=ChFlick" title="Documentation">📖</a></td>
+    <td align="center"><a href="https://github.com/Ascenio"><img src="https://avatars1.githubusercontent.com/u/7662016?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Ascênio</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/pulls?q=is%3Apr+reviewed-by%3AAscenio" title="Reviewed Pull Requests">👀</a></td>
+    <td align="center"><a href="https://www.linkedin.com/in/domenico-sibilio/"><img src="https://avatars2.githubusercontent.com/u/24280982?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Domenico Sibilio</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=dsibilio" title="Documentation">📖</a></td>
+    <td align="center"><a href="https://github.com/akashchandwani"><img src="https://avatars2.githubusercontent.com/u/3483277?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Akash Chandwani</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/pulls?q=is%3Apr+reviewed-by%3Aakashchandwani" title="Reviewed Pull Requests">👀</a></td>
+    <td align="center"><a href="http://www.linkedin.com/in/manannikov"><img src="https://avatars2.githubusercontent.com/u/7019769?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Pavlo Manannikov</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=manannikov" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/eimanip"><img src="https://avatars0.githubusercontent.com/u/20307301?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Eiman</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=eimanip" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/OrangePants-R"><img src="https://avatars0.githubusercontent.com/u/42976136?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Rocky</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=OrangePants-R" title="Documentation">📖</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://ibrahimalii.github.io/"><img src="https://avatars2.githubusercontent.com/u/21141301?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Ibrahim ali abdelghany</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/pulls?q=is%3Apr+reviewed-by%3AibrahimAlii" title="Reviewed Pull Requests">👀</a></td>
+    <td align="center"><a href="https://github.com/gkulkarni2020"><img src="https://avatars3.githubusercontent.com/u/5161548?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Girish Kulkarni</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=gkulkarni2020" title="Documentation">📖</a></td>
+    <td align="center"><a href="https://github.com/omk13"><img src="https://avatars0.githubusercontent.com/u/59054172?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Omar Karazoun</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=omk13" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/jeff303"><img src="https://avatars0.githubusercontent.com/u/3521562?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Jeff Evans</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=jeff303" title="Code">💻</a></td>
+    <td align="center"><a href="https://viveksb007.github.io"><img src="https://avatars1.githubusercontent.com/u/12713808?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Vivek Singh</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=viveksb007" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/siavashsoleymani"><img src="https://avatars2.githubusercontent.com/u/18074419?v=4?s=100" width="100px;" alt=""/><br /><sub><b>siavash</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=siavashsoleymani" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/ruchpeanuts"><img src="https://avatars0.githubusercontent.com/u/29301900?v=4?s=100" width="100px;" alt=""/><br /><sub><b>ruchpeanuts</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=ruchpeanuts" title="Documentation">📖</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/warp125"><img src="https://avatars1.githubusercontent.com/u/48073115?v=4?s=100" width="100px;" alt=""/><br /><sub><b>warp125</b></sub></a><br /><a href="#translation-warp125" title="Translation">🌍</a></td>
+    <td align="center"><a href="http://libkhadir.fr"><img src="https://avatars1.githubusercontent.com/u/45130488?v=4?s=100" width="100px;" alt=""/><br /><sub><b>KHADIR Tayeb</b></sub></a><br /><a href="#translation-tkhadir" title="Translation">🌍</a></td>
+    <td align="center"><a href="https://github.com/ignite1771"><img src="https://avatars2.githubusercontent.com/u/59446563?v=4?s=100" width="100px;" alt=""/><br /><sub><b>ignite1771</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=ignite1771" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/demirhalil"><img src="https://avatars1.githubusercontent.com/u/22895118?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Halil Demir</b></sub></a><br /><a href="#translation-demirhalil" title="Translation">🌍</a></td>
+    <td align="center"><a href="https://github.com/rohit10000"><img src="https://avatars.githubusercontent.com/u/20845565?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Rohit Singh</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=rohit10000" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/byoungju94"><img src="https://avatars.githubusercontent.com/u/42516378?v=4?s=100" width="100px;" alt=""/><br /><sub><b>byoungju94</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=byoungju94" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/moustafafarhat"><img src="https://avatars.githubusercontent.com/u/38836727?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Moustafa Farhat</b></sub></a><br /><a href="#translation-moustafafarhat" title="Translation">🌍</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/richardmr36"><img src="https://avatars.githubusercontent.com/u/19147333?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Martel Richard</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=richardmr36" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/va1m"><img src="https://avatars.githubusercontent.com/u/17025445?v=4?s=100" width="100px;" alt=""/><br /><sub><b>va1m</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=va1m" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/noamgrinch"><img src="https://avatars.githubusercontent.com/u/31648669?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Noam Greenshtain</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=noamgrinch" title="Code">💻</a></td>
+    <td align="center"><a href="https://xuyonghong.cn/"><img src="https://avatars.githubusercontent.com/u/14086462?v=4?s=100" width="100px;" alt=""/><br /><sub><b>yonghong Xu</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=qfxl" title="Documentation">📖</a></td>
+    <td align="center"><a href="https://www.linkedin.com/in/jinisha-vora"><img src="https://avatars.githubusercontent.com/u/40777762?v=4?s=100" width="100px;" alt=""/><br /><sub><b>jinishavora</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/pulls?q=is%3Apr+reviewed-by%3Ajinishavora" title="Reviewed Pull Requests">👀</a> <a href="https://github.com/iluwatar/java-design-patterns/commits?author=jinishavora" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/eas5"><img src="https://avatars.githubusercontent.com/u/50836521?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Elvys Soares</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=eas5" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/zWeBrain"><img src="https://avatars.githubusercontent.com/u/46642512?v=4?s=100" width="100px;" alt=""/><br /><sub><b>zWeBrain</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=zWeBrain" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://al-assad.github.io/notion/"><img src="https://avatars.githubusercontent.com/u/22493821?v=4?s=100" width="100px;" alt=""/><br /><sub><b>余林颖</b></sub></a><br /><a href="#translation-Al-assad" title="Translation">🌍</a></td>
+    <td align="center"><a href="https://github.com/STudio26"><img src="https://avatars.githubusercontent.com/u/6988911?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Alain</b></sub></a><br /><a href="#translation-STudio26" title="Translation">🌍</a></td>
+    <td align="center"><a href="https://github.com/DEV-VRUPER"><img src="https://avatars.githubusercontent.com/u/30525467?v=4?s=100" width="100px;" alt=""/><br /><sub><b>VR</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=DEV-VRUPER" title="Documentation">📖</a></td>
+    <td align="center"><a href="https://github.com/JackieNim"><img src="https://avatars.githubusercontent.com/u/4138836?v=4?s=100" width="100px;" alt=""/><br /><sub><b>JackieNim</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=JackieNim" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/EdisonE3"><img src="https://avatars.githubusercontent.com/u/52118917?v=4?s=100" width="100px;" alt=""/><br /><sub><b>EdisonE3</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=EdisonE3" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/tao-sun2"><img src="https://avatars.githubusercontent.com/u/66189688?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Tao</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=tao-sun2" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/JuanManuelAbate"><img src="https://avatars.githubusercontent.com/u/16357060?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Juan Manuel Abate</b></sub></a><br /><a href="#translation-JuanManuelAbate" title="Translation">🌍</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/Xenilo137"><img src="https://avatars.githubusercontent.com/u/24865069?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Xenilo137</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Xenilo137" title="Code">💻</a></td>
+    <td align="center"><a href="https://www.linkedin.com/in/souzasamuel/"><img src="https://avatars.githubusercontent.com/u/17254162?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Samuel Souza</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=samuelpsouza" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/marlo2222"><img src="https://avatars.githubusercontent.com/u/40809563?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Marlo Henrique</b></sub></a><br /><a href="#translation-marlo2222" title="Translation">🌍</a></td>
+    <td align="center"><a href="https://github.com/AndriyPyzh"><img src="https://avatars.githubusercontent.com/u/57706635?v=4?s=100" width="100px;" alt=""/><br /><sub><b>AndriyPyzh</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=AndriyPyzh" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/karthikbhat13"><img src="https://avatars.githubusercontent.com/u/22431014?v=4?s=100" width="100px;" alt=""/><br /><sub><b>karthikbhat13</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=karthikbhat13" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/mortezaadi"><img src="https://avatars.githubusercontent.com/u/1329687?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Morteza Adigozalpour</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=mortezaadi" title="Code">💻</a></td>
+    <td align="center"><a href="https://stackoverflow.com/users/308565/nagaraj-tantri"><img src="https://avatars.githubusercontent.com/u/3784194?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Nagaraj Tantri</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=tan31989" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="http://scuccimarri.it"><img src="https://avatars.githubusercontent.com/u/7107651?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Francesco Scuccimarri</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=frascu" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/Conhan93"><img src="https://avatars.githubusercontent.com/u/71334757?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Conny Hansson</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Conhan93" title="Documentation">📖</a></td>
+    <td align="center"><a href="http://muklasr.medium.com"><img src="https://avatars.githubusercontent.com/u/43443753?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Muklas Rahmanto</b></sub></a><br /><a href="#translation-muklasr" title="Translation">🌍</a></td>
+    <td align="center"><a href="https://github.com/VxDxK"><img src="https://avatars.githubusercontent.com/u/38704817?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Vadim</b></sub></a><br /><a href="#translation-VxDxK" title="Translation">🌍</a></td>
+    <td align="center"><a href="https://github.com/sims-keshri"><img src="https://avatars.githubusercontent.com/u/62168475?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Simran Keshri</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=sims-keshri" title="Code">💻</a></td>
+    <td align="center"><a href="https://programacionymas.com"><img src="https://avatars.githubusercontent.com/u/3101238?v=4?s=100" width="100px;" alt=""/><br /><sub><b>JCarlos</b></sub></a><br /><a href="#translation-JCarlosR" title="Translation">🌍</a></td>
+    <td align="center"><a href="https://www.mrmoshkel.ir"><img src="https://avatars.githubusercontent.com/u/60359433?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Ali Ghasemi</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Dev-AliGhasemi" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="http://carlfx.wordpress.com"><img src="https://avatars.githubusercontent.com/u/1594624?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Carl Dea</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=carldea" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/Mozartuss"><img src="https://avatars.githubusercontent.com/u/32893711?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Mozartus</b></sub></a><br /><a href="#translation-Mozartuss" title="Translation">🌍</a></td>
+    <td align="center"><a href="https://github.com/ManviGoel26"><img src="https://avatars.githubusercontent.com/u/55682355?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Manvi Goel</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=ManviGoel26" title="Documentation">📖</a></td>
+    <td align="center"><a href="https://github.com/blueberry404"><img src="https://avatars.githubusercontent.com/u/39243539?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Anum Amin</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=blueberry404" title="Documentation">📖</a></td>
+    <td align="center"><a href="https://uh-zz.github.io/blog/"><img src="https://avatars.githubusercontent.com/u/47747828?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Reo Uehara</b></sub></a><br /><a href="#translation-uh-zz" title="Translation">🌍</a></td>
+    <td align="center"><a href="https://github.com/Fiordy"><img src="https://avatars.githubusercontent.com/u/53420573?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Fiordy</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Fiordy" title="Documentation">📖</a></td>
+    <td align="center"><a href="https://github.com/harshalkh"><img src="https://avatars.githubusercontent.com/u/37841724?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Harshal</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=harshalkh" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://www.linkedin.com/in/abhinav-vashisth-06613b208/"><img src="https://avatars.githubusercontent.com/u/89785800?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Abhinav Vashisth</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=vashisthabhinav" title="Documentation">📖</a></td>
+    <td align="center"><a href="http://no website"><img src="https://avatars.githubusercontent.com/u/47126749?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Kevin</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/pulls?q=is%3Apr+reviewed-by%3AKevinyl3" title="Reviewed Pull Requests">👀</a> <a href="https://github.com/iluwatar/java-design-patterns/commits?author=Kevinyl3" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/Shrirang97"><img src="https://avatars.githubusercontent.com/u/28738668?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Shrirang</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/pulls?q=is%3Apr+reviewed-by%3AShrirang97" title="Reviewed Pull Requests">👀</a> <a href="https://github.com/iluwatar/java-design-patterns/commits?author=Shrirang97" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/interactwithankush"><img src="https://avatars.githubusercontent.com/u/18613127?v=4?s=100" width="100px;" alt=""/><br /><sub><b>interactwithankush</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=interactwithankush" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/yuhangbin"><img src="https://avatars.githubusercontent.com/u/17566866?v=4?s=100" width="100px;" alt=""/><br /><sub><b>CharlieYu</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=yuhangbin" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/Leisterbecker"><img src="https://avatars.githubusercontent.com/u/20650323?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Leisterbecker</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Leisterbecker" title="Code">💻</a></td>
+    <td align="center"><a href="http://rosaecrucis.cn"><img src="https://avatars.githubusercontent.com/u/35420129?v=4?s=100" width="100px;" alt=""/><br /><sub><b>DragonDreamer</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=castleKing1997" title="Code">💻</a></td>
+  </tr>
+  <tr>
+    <td align="center"><a href="https://github.com/ShivanshCharak"><img src="https://avatars.githubusercontent.com/u/96943825?v=4?s=100" width="100px;" alt=""/><br /><sub><b>ShivanshCharak</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=ShivanshCharak" title="Code">💻</a></td>
+    <td align="center"><a href="https://github.com/HattoriHenzo"><img src="https://avatars.githubusercontent.com/u/5141285?v=4?s=100" width="100px;" alt=""/><br /><sub><b>HattoriHenzo</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=HattoriHenzo" title="Code">💻</a></td>
+  </tr>
+</table>
+
+<!-- markdownlint-restore -->
+<!-- prettier-ignore-end -->
+
+<!-- ALL-CONTRIBUTORS-LIST:END -->

abstract-document/README.md

@@ -4,26 +4,188 @@ title: Abstract Document
 folder: abstract-document
 permalink: /patterns/abstract-document/
 categories: Structural
+language: en
 tags: 
- - Java
- - Difficulty-Intermediate
+ - Extensibility
 ---
 
 ## Intent
-Achieve flexibility of untyped languages and keep the type-safety 
+
+Use dynamic properties and achieve flexibility of untyped languages while keeping type-safety. 
+
+## Explanation
+
+The Abstract Document pattern enables handling additional, non-static properties. This pattern
+uses concept of traits to enable type safety and separate properties of different classes into
+set of interfaces.
+
+Real world example
+
+>  Consider a car that consists of multiple parts. However we don't know if the specific car really has all the parts, or just some of them. Our cars are dynamic and extremely flexible.
+
+In plain words
+
+> Abstract Document pattern allows attaching properties to objects without them knowing about it.
+
+Wikipedia says
+
+> An object-oriented structural design pattern for organizing objects in loosely typed key-value stores and exposing 
+the data using typed views. The purpose of the pattern is to achieve a high degree of flexibility between components 
+in a strongly typed language where new properties can be added to the object-tree on the fly, without losing the 
+support of type-safety. The pattern makes use of traits to separate different properties of a class into different 
+interfaces.
+
+**Programmatic Example**
+
+Let's first define the base classes `Document` and `AbstractDocument`. They basically make the object hold a property
+map and any amount of child objects.
+
+```java
+public interface Document {
+
+  Void put(String key, Object value);
+
+  Object get(String key);
+
+  <T> Stream<T> children(String key, Function<Map<String, Object>, T> constructor);
+}
+
+public abstract class AbstractDocument implements Document {
+
+  private final Map<String, Object> properties;
+
+  protected AbstractDocument(Map<String, Object> properties) {
+    Objects.requireNonNull(properties, "properties map is required");
+    this.properties = properties;
+  }
+
+  @Override
+  public Void put(String key, Object value) {
+    properties.put(key, value);
+    return null;
+  }
+
+  @Override
+  public Object get(String key) {
+    return properties.get(key);
+  }
+
+  @Override
+  public <T> Stream<T> children(String key, Function<Map<String, Object>, T> constructor) {
+    return Stream.ofNullable(get(key))
+        .filter(Objects::nonNull)
+        .map(el -> (List<Map<String, Object>>) el)
+        .findAny()
+        .stream()
+        .flatMap(Collection::stream)
+        .map(constructor);
+  }
+  ...
+}
+```
+Next we define an enum `Property` and a set of interfaces for type, price, model and parts. This allows us to create
+static looking interface to our `Car` class.
+
+```java
+public enum Property {
+
+  PARTS, TYPE, PRICE, MODEL
+}
+
+public interface HasType extends Document {
+
+  default Optional<String> getType() {
+    return Optional.ofNullable((String) get(Property.TYPE.toString()));
+  }
+}
+
+public interface HasPrice extends Document {
+
+  default Optional<Number> getPrice() {
+    return Optional.ofNullable((Number) get(Property.PRICE.toString()));
+  }
+}
+public interface HasModel extends Document {
+
+  default Optional<String> getModel() {
+    return Optional.ofNullable((String) get(Property.MODEL.toString()));
+  }
+}
+
+public interface HasParts extends Document {
+
+  default Stream<Part> getParts() {
+    return children(Property.PARTS.toString(), Part::new);
+  }
+}
+```
+
+Now we are ready to introduce the `Car`.
+
+```java
+public class Car extends AbstractDocument implements HasModel, HasPrice, HasParts {
+
+  public Car(Map<String, Object> properties) {
+    super(properties);
+  }
+}
+```
+
+And finally here's how we construct and use the `Car` in a full example.
+
+```java
+    LOGGER.info("Constructing parts and car");
+
+    var wheelProperties = Map.of(
+        Property.TYPE.toString(), "wheel",
+        Property.MODEL.toString(), "15C",
+        Property.PRICE.toString(), 100L);
+
+    var doorProperties = Map.of(
+        Property.TYPE.toString(), "door",
+        Property.MODEL.toString(), "Lambo",
+        Property.PRICE.toString(), 300L);
+
+    var carProperties = Map.of(
+        Property.MODEL.toString(), "300SL",
+        Property.PRICE.toString(), 10000L,
+        Property.PARTS.toString(), List.of(wheelProperties, doorProperties));
+
+    var car = new Car(carProperties);
+
+    LOGGER.info("Here is our car:");
+    LOGGER.info("-> model: {}", car.getModel().orElseThrow());
+    LOGGER.info("-> price: {}", car.getPrice().orElseThrow());
+    LOGGER.info("-> parts: ");
+    car.getParts().forEach(p -> LOGGER.info("\t{}/{}/{}",
+        p.getType().orElse(null),
+        p.getModel().orElse(null),
+        p.getPrice().orElse(null))
+    );
+
+    // Constructing parts and car
+    // Here is our car:
+    // model: 300SL
+    // price: 10000
+    // parts: 
+    // wheel/15C/100
+    // door/Lambo/300
+```
+
+## Class diagram
 
 ![alt text](./etc/abstract-document.png "Abstract Document Traits and Domain")
 
-
 ## Applicability
+
 Use the Abstract Document Pattern when
 
-* there is a need to add new properties on the fly
-* you want a flexible way to organize domain in tree like structure
-* you want more loosely coupled system
-
+* There is a need to add new properties on the fly
+* You want a flexible way to organize domain in tree like structure
+* You want more loosely coupled system
 
 ## Credits
 
 * [Wikipedia: Abstract Document Pattern](https://en.wikipedia.org/wiki/Abstract_Document_Pattern)
-* [Martin Fowler: Dealing with properties](http://martinfowler.com/apsupp/properties.pdf)
+* [Martin Fowler: Dealing with properties](http://martinfowler.com/apsupp/properties.pdf)
+* [Pattern-Oriented Software Architecture Volume 4: A Pattern Language for Distributed Computing (v. 4)](https://www.amazon.com/gp/product/0470059028/ref=as_li_qf_asin_il_tl?ie=UTF8&tag=javadesignpat-20&creative=9325&linkCode=as2&creativeASIN=0470059028&linkId=e3aacaea7017258acf184f9f3283b492)

abstract-document/etc/abstract-document.urm.puml

@@ -0,0 +1,65 @@
+@startuml
+package com.iluwatar.abstractdocument.domain.enums {
+  enum Property {
+    + MODEL {static}
+    + PARTS {static}
+    + PRICE {static}
+    + TYPE {static}
+    + valueOf(name : String) : Property {static}
+    + values() : Property[] {static}
+  }
+}
+package com.iluwatar.abstractdocument.domain {
+  class Car {
+    + Car(properties : Map<String, Object>)
+  }
+  interface HasModel {
+    + getModel() : Optional<String>
+  }
+  interface HasParts {
+    + getParts() : Stream<Part>
+  }
+  interface HasPrice {
+    + getPrice() : Optional<Number>
+  }
+  interface HasType {
+    + getType() : Optional<String>
+  }
+  class Part {
+    + Part(properties : Map<String, Object>)
+  }
+}
+package com.iluwatar.abstractdocument {
+  abstract class AbstractDocument {
+    - properties : Map<String, Object>
+    # AbstractDocument(properties : Map<String, Object>)
+    + children(key : String, constructor : Function<Map<String, Object>, T>) : Stream<T>
+    + get(key : String) : Object
+    + put(key : String, value : Object)
+    + toString() : String
+  }
+  class App {
+    - LOGGER : Logger {static}
+    + App()
+    + main(args : String[]) {static}
+  }
+  interface Document {
+    + children(String, Function<Map<String, Object>, T>) : Stream<T> {abstract}
+    + get(String) : Object {abstract}
+    + put(String, Object) {abstract}
+  }
+}
+AbstractDocument ..|> Document 
+Car ..|> HasModel 
+Car ..|> HasPrice 
+Car ..|> HasParts 
+Car --|> AbstractDocument 
+HasModel --|> Document 
+HasParts --|> Document 
+HasPrice --|> Document 
+HasType --|> Document 
+Part ..|> HasType 
+Part ..|> HasModel 
+Part ..|> HasPrice 
+Part --|> AbstractDocument 
+@enduml

abstract-document/pom.xml

@@ -2,7 +2,7 @@
 <!--
 
     The MIT License
-    Copyright © 2014-2019 Ilkka Seppälä
+    Copyright © 2014-2021 Ilkka Seppälä
 
     Permission is hereby granted, free of charge, to any person obtaining a copy
     of this software and associated documentation files (the "Software"), to deal
@@ -23,20 +23,40 @@
     THE SOFTWARE.
 
 -->
-<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
-    <modelVersion>4.0.0</modelVersion>
-    <parent>
-        <artifactId>java-design-patterns</artifactId>
-        <groupId>com.iluwatar</groupId>
-        <version>1.22.0-SNAPSHOT</version>
-    </parent>
-    <artifactId>abstract-document</artifactId>
-    <dependencies>
-        <dependency>
-            <groupId>org.junit.jupiter</groupId>
-            <artifactId>junit-jupiter-engine</artifactId>
-            <scope>test</scope>
-        </dependency>
-    </dependencies>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <artifactId>java-design-patterns</artifactId>
+    <groupId>com.iluwatar</groupId>
+    <version>1.26.0-SNAPSHOT</version>
+  </parent>
+  <artifactId>abstract-document</artifactId>
+  <dependencies>
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-engine</artifactId>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+  <build>
+    <plugins>
+      <!-- Maven assembly plugin is invoked with default setting which we have 
+				in parent pom and specifying the class having main method -->
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-assembly-plugin</artifactId>
+        <executions>
+          <execution>
+            <configuration>
+              <archive>
+                <manifest>
+                  <mainClass>com.iluwatar.abstractdocument.App</mainClass>
+                </manifest>
+              </archive>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
 </project>

abstract-document/src/main/java/com/iluwatar/abstractdocument/AbstractDocument.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal

abstract-document/src/main/java/com/iluwatar/abstractdocument/App.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -27,8 +27,7 @@ import com.iluwatar.abstractdocument.domain.Car;
 import com.iluwatar.abstractdocument.domain.enums.Property;
 import java.util.List;
 import java.util.Map;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
+import lombok.extern.slf4j.Slf4j;
 
 /**
  * The Abstract Document pattern enables handling additional, non-static properties. This pattern
@@ -38,14 +37,15 @@ import org.slf4j.LoggerFactory;
  * <p>In Abstract Document pattern,({@link AbstractDocument}) fully implements {@link Document})
  * interface. Traits are then defined to enable access to properties in usual, static way.
  */
+@Slf4j
 public class App {
 
-  private static final Logger LOGGER = LoggerFactory.getLogger(App.class);
-
   /**
-   * Executes the App.
+   * Program entry point.
+   *
+   * @param args command line args
    */
-  public App() {
+  public static void main(String[] args) {
     LOGGER.info("Constructing parts and car");
 
     var wheelProperties = Map.of(
@@ -75,14 +75,4 @@ public class App {
         p.getPrice().orElse(null))
     );
   }
-
-  /**
-   * Program entry point.
-   *
-   * @param args command line args
-   */
-  public static void main(String[] args) {
-    new App();
-  }
-
 }

abstract-document/src/main/java/com/iluwatar/abstractdocument/Document.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal

abstract-document/src/main/java/com/iluwatar/abstractdocument/domain/Car.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal

abstract-document/src/main/java/com/iluwatar/abstractdocument/domain/HasModel.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal

abstract-document/src/main/java/com/iluwatar/abstractdocument/domain/HasParts.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -32,7 +32,6 @@ import java.util.stream.Stream;
  */
 public interface HasParts extends Document {
 
-
   default Stream<Part> getParts() {
     return children(Property.PARTS.toString(), Part::new);
   }

abstract-document/src/main/java/com/iluwatar/abstractdocument/domain/HasPrice.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -32,7 +32,6 @@ import java.util.Optional;
  */
 public interface HasPrice extends Document {
 
-
   default Optional<Number> getPrice() {
     return Optional.ofNullable((Number) get(Property.PRICE.toString()));
   }

abstract-document/src/main/java/com/iluwatar/abstractdocument/domain/HasType.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -32,7 +32,6 @@ import java.util.Optional;
  */
 public interface HasType extends Document {
 
-
   default Optional<String> getType() {
     return Optional.ofNullable((String) get(Property.TYPE.toString()));
   }

abstract-document/src/main/java/com/iluwatar/abstractdocument/domain/Part.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal

abstract-document/src/main/java/com/iluwatar/abstractdocument/domain/enums/Property.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal

abstract-document/src/test/java/com/iluwatar/abstractdocument/AbstractDocumentTest.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -23,40 +23,39 @@
 
 package com.iluwatar.abstractdocument;
 
-import static org.junit.jupiter.api.Assertions.assertEquals;
-import static org.junit.jupiter.api.Assertions.assertNotNull;
-import static org.junit.jupiter.api.Assertions.assertTrue;
+import org.junit.jupiter.api.Test;
 
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
-import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
 
 /**
  * AbstractDocument test class
  */
-public class AbstractDocumentTest {
+class AbstractDocumentTest {
 
   private static final String KEY = "key";
   private static final String VALUE = "value";
 
-  private class DocumentImplementation extends AbstractDocument {
+  private static class DocumentImplementation extends AbstractDocument {
 
     DocumentImplementation(Map<String, Object> properties) {
       super(properties);
     }
   }
 
-  private DocumentImplementation document = new DocumentImplementation(new HashMap<>());
+  private final DocumentImplementation document = new DocumentImplementation(new HashMap<>());
 
   @Test
-  public void shouldPutAndGetValue() {
+  void shouldPutAndGetValue() {
     document.put(KEY, VALUE);
     assertEquals(VALUE, document.get(KEY));
   }
 
   @Test
-  public void shouldRetrieveChildren() {
+  void shouldRetrieveChildren() {
     var children = List.of(Map.of(), Map.of());
 
     document.put(KEY, children);
@@ -67,14 +66,14 @@ public class AbstractDocumentTest {
   }
 
   @Test
-  public void shouldRetrieveEmptyStreamForNonExistingChildren() {
+  void shouldRetrieveEmptyStreamForNonExistingChildren() {
     var children = document.children(KEY, DocumentImplementation::new);
     assertNotNull(children);
     assertEquals(0, children.count());
   }
 
   @Test
-  public void shouldIncludePropsInToString() {
+  void shouldIncludePropsInToString() {
     var props = Map.of(KEY, (Object) VALUE);
     var document = new DocumentImplementation(props);
     assertTrue(document.toString().contains(KEY));

abstract-document/src/test/java/com/iluwatar/abstractdocument/AppTest.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -25,14 +25,23 @@ package com.iluwatar.abstractdocument;
 
 import org.junit.jupiter.api.Test;
 
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+
 /**
  * Simple App test
  */
-public class AppTest {
+class AppTest {
+
+  /**
+   * Issue: Add at least one assertion to this test case.
+   *
+   * Solution: Inserted assertion to check whether the execution of the main method in {@link App}
+   * throws an exception.
+   */
 
   @Test
-  public void shouldExecuteAppWithoutException() {
-    App.main(null);
+  void shouldExecuteAppWithoutException() {
+    assertDoesNotThrow(() -> App.main(null));
   }
 
 }

abstract-document/src/test/java/com/iluwatar/abstractdocument/DomainTest.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -23,19 +23,20 @@
 
 package com.iluwatar.abstractdocument;
 
-import static org.junit.jupiter.api.Assertions.assertEquals;
-
 import com.iluwatar.abstractdocument.domain.Car;
 import com.iluwatar.abstractdocument.domain.Part;
 import com.iluwatar.abstractdocument.domain.enums.Property;
+import org.junit.jupiter.api.Test;
+
 import java.util.List;
 import java.util.Map;
-import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
 /**
  * Test for Part and Car
  */
-public class DomainTest {
+class DomainTest {
 
   private static final String TEST_PART_TYPE = "test-part-type";
   private static final String TEST_PART_MODEL = "test-part-model";
@@ -45,7 +46,7 @@ public class DomainTest {
   private static final long TEST_CAR_PRICE = 1L;
 
   @Test
-  public void shouldConstructPart() {
+  void shouldConstructPart() {
     var partProperties = Map.of(
         Property.TYPE.toString(), TEST_PART_TYPE,
         Property.MODEL.toString(), TEST_PART_MODEL,
@@ -58,7 +59,7 @@ public class DomainTest {
   }
 
   @Test
-  public void shouldConstructCar() {
+  void shouldConstructCar() {
     var carProperties = Map.of(
         Property.MODEL.toString(), TEST_CAR_MODEL,
         Property.PRICE.toString(), TEST_CAR_PRICE,

abstract-factory/README.md

@@ -4,23 +4,25 @@ title: Abstract Factory
 folder: abstract-factory
 permalink: /patterns/abstract-factory/
 categories: Creational
+language: en
 tags:
- - Java
- - Gang Of Four
- - Difficulty-Intermediate
+ - Gang of Four
 ---
 
 ## Also known as
+
 Kit
 
 ## Intent
+
 Provide an interface for creating families of related or dependent
 objects without specifying their concrete classes.
 
 ## Explanation
-Real world example
 
-> To create a kingdom we need objects with common theme. Elven kingdom needs an Elven king, Elven castle and Elven army whereas Orcish kingdom needs an Orcish king, Orcish castle and Orcish army. There is a dependency between the objects in the kingdom.
+Real-world example
+
+> To create a kingdom we need objects with a common theme. The elven kingdom needs an elven king, elven castle, and elven army whereas the orcish kingdom needs an orcish king, orcish castle, and orcish army. There is a dependency between the objects in the kingdom.
 
 In plain words
 
@@ -32,47 +34,50 @@ Wikipedia says
 
 **Programmatic Example**
 
-Translating the kingdom example above. First of all we have some interfaces and implementation for the objects in the kingdom
+Translating the kingdom example above. First of all, we have some interfaces and implementation for the objects in the 
+kingdom.
 
 ```java
 public interface Castle {
   String getDescription();
 }
+
 public interface King {
   String getDescription();
 }
+
 public interface Army {
   String getDescription();
 }
 
 // Elven implementations ->
 public class ElfCastle implements Castle {
-  static final String DESCRIPTION = "This is the Elven castle!";
+  static final String DESCRIPTION = "This is the elven castle!";
   @Override
   public String getDescription() {
     return DESCRIPTION;
   }
 }
 public class ElfKing implements King {
-  static final String DESCRIPTION = "This is the Elven king!";
+  static final String DESCRIPTION = "This is the elven king!";
   @Override
   public String getDescription() {
     return DESCRIPTION;
   }
 }
 public class ElfArmy implements Army {
-  static final String DESCRIPTION = "This is the Elven Army!";
+  static final String DESCRIPTION = "This is the elven Army!";
   @Override
   public String getDescription() {
     return DESCRIPTION;
   }
 }
 
-// Orcish implementations similarly...
+// Orcish implementations similarly -> ...
 
 ```
 
-Then we have the abstraction and implementations for the kingdom factory
+Then we have the abstraction and implementations for the kingdom factory.
 
 ```java
 public interface KingdomFactory {
@@ -82,31 +87,43 @@ public interface KingdomFactory {
 }
 
 public class ElfKingdomFactory implements KingdomFactory {
+
+  @Override
   public Castle createCastle() {
     return new ElfCastle();
   }
+
+  @Override
   public King createKing() {
     return new ElfKing();
   }
+
+  @Override
   public Army createArmy() {
     return new ElfArmy();
   }
 }
 
 public class OrcKingdomFactory implements KingdomFactory {
+
+  @Override
   public Castle createCastle() {
     return new OrcCastle();
   }
+
+  @Override
   public King createKing() {
     return new OrcKing();
   }
+  
+  @Override
   public Army createArmy() {
     return new OrcArmy();
   }
 }
 ```
 
-Now we have our abstract factory that lets us make family of related objects i.e. Elven kingdom factory creates Elven castle, king and army etc.
+Now we have the abstract factory that lets us make a family of related objects i.e. elven kingdom factory creates elven castle, king and army, etc.
 
 ```java
 var factory = new ElfKingdomFactory();
@@ -114,13 +131,21 @@ var castle = factory.createCastle();
 var king = factory.createKing();
 var army = factory.createArmy();
 
-castle.getDescription();  // Output: This is the Elven castle!
-king.getDescription(); // Output: This is the Elven king!
-army.getDescription(); // Output: This is the Elven Army!
+castle.getDescription();
+king.getDescription();
+army.getDescription();
 ```
 
-Now, we can design a factory for our different kingdom factories. In this example, we created FactoryMaker, responsible for returning an instance of either ElfKingdomFactory or OrcKingdomFactory.  
-The client can use FactoryMaker to create the desired concrete factory which, in turn, will produce different concrete objects (Army, King, Castle).  
+Program output:
+
+```java
+This is the elven castle!
+This is the elven king!
+This is the elven Army!
+```
+
+Now, we can design a factory for our different kingdom factories. In this example, we created `FactoryMaker`, responsible for returning an instance of either `ElfKingdomFactory` or `OrcKingdomFactory`.  
+The client can use `FactoryMaker` to create the desired concrete factory which, in turn, will produce different concrete objects (derived from `Army`, `King`, `Castle`).  
 In this example, we also used an enum to parameterize which type of kingdom factory the client will ask for.
 
 ```java
@@ -157,44 +182,54 @@ public static void main(String[] args) {
 }
 ```
 
+## Class diagram
+
+![alt text](./etc/abstract-factory.urm.png "Abstract Factory class diagram")
+
 
 ## Applicability
+
 Use the Abstract Factory pattern when
 
-* a system should be independent of how its products are created, composed and represented
-* a system should be configured with one of multiple families of products
-* a family of related product objects is designed to be used together, and you need to enforce this constraint
-* you want to provide a class library of products, and you want to reveal just their interfaces, not their implementations
-* the lifetime of the dependency is conceptually shorter than the lifetime of the consumer.
-*	you need a run-time value to construct a particular dependency
-*	you want to decide which product to call from a family at runtime.
-*	you need to supply one or more parameters only known at run-time before you can resolve a dependency.
-* when you need consistency among products
-* you don’t want to change existing code when adding new products or families of products to the program.
+* The system should be independent of how its products are created, composed, and represented
+* The system should be configured with one of the multiple families of products
+* The family of related product objects is designed to be used together, and you need to enforce this constraint
+* You want to provide a class library of products, and you want to reveal just their interfaces, not their implementations
+* The lifetime of the dependency is conceptually shorter than the lifetime of the consumer.
+* You need a run-time value to construct a particular dependency
+* You want to decide which product to call from a family at runtime.
+* You need to supply one or more parameters only known at run-time before you can resolve a dependency.
+* When you need consistency among products
+* You don’t want to change existing code when adding new products or families of products to the program.
 
-## Use Cases:	
+Example use cases	
 
-*	Selecting to call the appropriate implementation of FileSystemAcmeService or DatabaseAcmeService or NetworkAcmeService at runtime.
-*	Unit test case writing becomes much easier
+* Selecting to call to the appropriate implementation of FileSystemAcmeService or DatabaseAcmeService or NetworkAcmeService at runtime.
+* Unit test case writing becomes much easier
 * UI tools for different OS
 
-## Consequences:
+## Consequences
 
-*	Dependency injection in java hides the service class dependencies that can lead to runtime errors that would have been caught at compile time.
+* Dependency injection in java hides the service class dependencies that can lead to runtime errors that would have been caught at compile time.
 * While the pattern is great when creating predefined objects, adding the new ones might be challenging.
-* The code may become more complicated than it should be, since a lot of new interfaces and classes are introduced along with the pattern.
+* The code becomes more complicated than it should be since a lot of new interfaces and classes are introduced along with the pattern.
 
+## Tutorials
 
-## Tutorial
 * [Abstract Factory Pattern Tutorial](https://www.journaldev.com/1418/abstract-factory-design-pattern-in-java) 
 
-
-## Real world examples
+## Known uses
 
 * [javax.xml.parsers.DocumentBuilderFactory](http://docs.oracle.com/javase/8/docs/api/javax/xml/parsers/DocumentBuilderFactory.html)
 * [javax.xml.transform.TransformerFactory](http://docs.oracle.com/javase/8/docs/api/javax/xml/transform/TransformerFactory.html#newInstance--)
 * [javax.xml.xpath.XPathFactory](http://docs.oracle.com/javase/8/docs/api/javax/xml/xpath/XPathFactory.html#newInstance--)
 
+## Related patterns
+
+* [Factory Method](https://java-design-patterns.com/patterns/factory-method/)
+* [Factory Kit](https://java-design-patterns.com/patterns/factory-kit/)
+
 ## Credits
 
-* [Design Patterns: Elements of Reusable Object-Oriented Software](http://www.amazon.com/Design-Patterns-Elements-Reusable-Object-Oriented/dp/0201633612)
+* [Design Patterns: Elements of Reusable Object-Oriented Software](https://www.amazon.com/gp/product/0201633612/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0201633612&linkCode=as2&tag=javadesignpat-20&linkId=675d49790ce11db99d90bde47f1aeb59)
+* [Head First Design Patterns: A Brain-Friendly Guide](https://www.amazon.com/gp/product/0596007124/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0596007124&linkCode=as2&tag=javadesignpat-20&linkId=6b8b6eea86021af6c8e3cd3fc382cb5b)

abstract-factory/etc/abstract-factory.urm.puml

@@ -0,0 +1,101 @@
+@startuml
+package com.iluwatar.abstractfactory {
+  class App {
+    - LOGGER : Logger {static}
+    - army : Army
+    - castle : Castle
+    - king : King
+    + App()
+    + createKingdom(factory : KingdomFactory)
+    + getArmy() : Army
+    ~ getArmy(factory : KingdomFactory) : Army
+    + getCastle() : Castle
+    ~ getCastle(factory : KingdomFactory) : Castle
+    + getKing() : King
+    ~ getKing(factory : KingdomFactory) : King
+    + main(args : String[]) {static}
+    - setArmy(army : Army)
+    - setCastle(castle : Castle)
+    - setKing(king : King)
+  }
+  class FactoryMaker {
+    + FactoryMaker()
+    + makeFactory(type : KingdomType) : KingdomFactory {static}
+  }
+  enum KingdomType {
+    + ELF {static}
+    + ORC {static}
+    + valueOf(name : String) : KingdomType {static}
+    + values() : KingdomType[] {static}
+  }
+  interface Army {
+    + getDescription() : String {abstract}
+  }
+  interface Castle {
+    + getDescription() : String {abstract}
+  }
+  class ElfArmy {
+    ~ DESCRIPTION : String {static}
+    + ElfArmy()
+    + getDescription() : String
+  }
+  class ElfCastle {
+    ~ DESCRIPTION : String {static}
+    + ElfCastle()
+    + getDescription() : String
+  }
+  class ElfKing {
+    ~ DESCRIPTION : String {static}
+    + ElfKing()
+    + getDescription() : String
+  }
+  class ElfKingdomFactory {
+    + ElfKingdomFactory()
+    + createArmy() : Army
+    + createCastle() : Castle
+    + createKing() : King
+  }
+  interface King {
+    + getDescription() : String {abstract}
+  }
+  interface KingdomFactory {
+    + createArmy() : Army {abstract}
+    + createCastle() : Castle {abstract}
+    + createKing() : King {abstract}
+  }
+  class OrcArmy {
+    ~ DESCRIPTION : String {static}
+    + OrcArmy()
+    + getDescription() : String
+  }
+  class OrcCastle {
+    ~ DESCRIPTION : String {static}
+    + OrcCastle()
+    + getDescription() : String
+  }
+  class OrcKing {
+    ~ DESCRIPTION : String {static}
+    + OrcKing()
+    + getDescription() : String
+  }
+  class OrcKingdomFactory {
+    + OrcKingdomFactory()
+    + createArmy() : Army
+    + createCastle() : Castle
+    + createKing() : King
+  }
+}
+KingdomType ..+ FactoryMaker
+App -->  "-castle" Castle
+FactoryMaker ..+ App
+App -->  "-king" King
+App -->  "-army" Army
+ElfArmy ..|> Army 
+ElfCastle ..|> Castle 
+ElfKing ..|> King 
+ElfKingdomFactory ..|> KingdomFactory 
+OrcArmy ..|> Army 
+OrcCastle ..|> Castle 
+OrcKing ..|> King 
+OrcKingdomFactory ..|> KingdomFactory 
+@enduml

abstract-factory/pom.xml

@@ -1,8 +1,8 @@
-<?xml version="1.0"?>
+<?xml version="1.0" encoding="UTF-8"?>
 <!--
 
     The MIT License
-    Copyright © 2014-2019 Ilkka Seppälä
+    Copyright © 2014-2021 Ilkka Seppälä
 
     Permission is hereby granted, free of charge, to any person obtaining a copy
     of this software and associated documentation files (the "Software"), to deal
@@ -23,13 +23,12 @@
     THE SOFTWARE.
 
 -->
-<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
-    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.22.0-SNAPSHOT</version>
+    <version>1.26.0-SNAPSHOT</version>
   </parent>
   <artifactId>abstract-factory</artifactId>
   <dependencies>
@@ -39,4 +38,25 @@
       <scope>test</scope>
     </dependency>
   </dependencies>
+  <build>
+    <plugins>
+      <!-- Maven assembly plugin is invoked with default setting which we have 
+				in parent pom and specifying the class having main method -->
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-assembly-plugin</artifactId>
+        <executions>
+          <execution>
+            <configuration>
+              <archive>
+                <manifest>
+                  <mainClass>com.iluwatar.abstractfactory.App</mainClass>
+                </manifest>
+              </archive>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
 </project>

abstract-factory/src/main/java/com/iluwatar/abstractfactory/App.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -23,9 +23,7 @@
 
 package com.iluwatar.abstractfactory;
 
-import com.iluwatar.abstractfactory.App.FactoryMaker.KingdomType;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
+import lombok.extern.slf4j.Slf4j;
 
 /**
  * The Abstract Factory pattern provides a way to encapsulate a group of individual factories that
@@ -39,86 +37,15 @@ import org.slf4j.LoggerFactory;
  *
  * <p>The essence of the Abstract Factory pattern is a factory interface ({@link KingdomFactory})
  * and its implementations ( {@link ElfKingdomFactory}, {@link OrcKingdomFactory}). The example uses
- * both concrete implementations to create a king, a castle and an army.
+ * both concrete implementations to create a king, a castle, and an army.
  */
-public class App {
+@Slf4j
+public class App implements Runnable {
 
-  private static final Logger LOGGER = LoggerFactory.getLogger(App.class);
+  private final Kingdom kingdom = new Kingdom();
 
-  private King king;
-  private Castle castle;
-  private Army army;
-
-  /**
-   * Creates kingdom.
-   */
-  public void createKingdom(final KingdomFactory factory) {
-    setKing(factory.createKing());
-    setCastle(factory.createCastle());
-    setArmy(factory.createArmy());
-  }
-
-  King getKing(final KingdomFactory factory) {
-    return factory.createKing();
-  }
-
-  public King getKing() {
-    return king;
-  }
-
-  private void setKing(final King king) {
-    this.king = king;
-  }
-
-  Castle getCastle(final KingdomFactory factory) {
-    return factory.createCastle();
-  }
-
-  public Castle getCastle() {
-    return castle;
-  }
-
-  private void setCastle(final Castle castle) {
-    this.castle = castle;
-  }
-
-  Army getArmy(final KingdomFactory factory) {
-    return factory.createArmy();
-  }
-
-  public Army getArmy() {
-    return army;
-  }
-
-  private void setArmy(final Army army) {
-    this.army = army;
-  }
-
-  /**
-   * The factory of kingdom factories.
-   */
-  public static class FactoryMaker {
-
-    /**
-     * Enumeration for the different types of Kingdoms.
-     */
-    public enum KingdomType {
-      ELF, ORC
-    }
-
-    /**
-     * The factory method to create KingdomFactory concrete objects.
-     */
-    public static KingdomFactory makeFactory(KingdomType type) {
-      switch (type) {
-        case ELF:
-          return new ElfKingdomFactory();
-        case ORC:
-          return new OrcKingdomFactory();
-        default:
-          throw new IllegalArgumentException("KingdomType not supported.");
-      }
-    }
+  public Kingdom getKingdom() {
+    return kingdom;
   }
 
   /**
@@ -127,19 +54,33 @@ public class App {
    * @param args command line args
    */
   public static void main(String[] args) {
-
     var app = new App();
+    app.run();
+  }
 
-    LOGGER.info("Elf Kingdom");
-    app.createKingdom(FactoryMaker.makeFactory(KingdomType.ELF));
-    LOGGER.info(app.getArmy().getDescription());
-    LOGGER.info(app.getCastle().getDescription());
-    LOGGER.info(app.getKing().getDescription());
+  @Override
+  public void run() {
+    LOGGER.info("elf kingdom");
+    createKingdom(Kingdom.FactoryMaker.KingdomType.ELF);
+    LOGGER.info(kingdom.getArmy().getDescription());
+    LOGGER.info(kingdom.getCastle().getDescription());
+    LOGGER.info(kingdom.getKing().getDescription());
 
-    LOGGER.info("Orc Kingdom");
-    app.createKingdom(FactoryMaker.makeFactory(KingdomType.ORC));
-    LOGGER.info(app.getArmy().getDescription());
-    LOGGER.info(app.getCastle().getDescription());
-    LOGGER.info(app.getKing().getDescription());
+    LOGGER.info("orc kingdom");
+    createKingdom(Kingdom.FactoryMaker.KingdomType.ORC);
+    LOGGER.info(kingdom.getArmy().getDescription());
+    LOGGER.info(kingdom.getCastle().getDescription());
+    LOGGER.info(kingdom.getKing().getDescription());
+  }
+
+  /**
+   * Creates kingdom.
+   * @param kingdomType type of Kingdom
+   */
+  public void createKingdom(final Kingdom.FactoryMaker.KingdomType kingdomType) {
+    final KingdomFactory kingdomFactory = Kingdom.FactoryMaker.makeFactory(kingdomType);
+    kingdom.setKing(kingdomFactory.createKing());
+    kingdom.setCastle(kingdomFactory.createCastle());
+    kingdom.setArmy(kingdomFactory.createArmy());
   }
 }

abstract-factory/src/main/java/com/iluwatar/abstractfactory/Army.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal

abstract-factory/src/main/java/com/iluwatar/abstractfactory/Castle.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal

abstract-factory/src/main/java/com/iluwatar/abstractfactory/ElfArmy.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -28,7 +28,7 @@ package com.iluwatar.abstractfactory;
  */
 public class ElfArmy implements Army {
 
-  static final String DESCRIPTION = "This is the Elven Army!";
+  static final String DESCRIPTION = "This is the elven army!";
 
   @Override
   public String getDescription() {

abstract-factory/src/main/java/com/iluwatar/abstractfactory/ElfCastle.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -28,7 +28,7 @@ package com.iluwatar.abstractfactory;
  */
 public class ElfCastle implements Castle {
 
-  static final String DESCRIPTION = "This is the Elven castle!";
+  static final String DESCRIPTION = "This is the elven castle!";
 
   @Override
   public String getDescription() {

abstract-factory/src/main/java/com/iluwatar/abstractfactory/ElfKing.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -28,7 +28,7 @@ package com.iluwatar.abstractfactory;
  */
 public class ElfKing implements King {
 
-  static final String DESCRIPTION = "This is the Elven king!";
+  static final String DESCRIPTION = "This is the elven king!";
 
   @Override
   public String getDescription() {

abstract-factory/src/main/java/com/iluwatar/abstractfactory/ElfKingdomFactory.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal

abstract-factory/src/main/java/com/iluwatar/abstractfactory/King.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal

abstract-factory/src/main/java/com/iluwatar/abstractfactory/Kingdom.java

@@ -0,0 +1,63 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2021 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.abstractfactory;
+
+import lombok.Getter;
+import lombok.Setter;
+
+@Getter
+@Setter
+public class Kingdom {
+
+  private King king;
+  private Castle castle;
+  private Army army;
+
+  /**
+   * The factory of kingdom factories.
+   */
+  public static class FactoryMaker {
+
+    /**
+     * Enumeration for the different types of Kingdoms.
+     */
+    public enum KingdomType {
+      ELF, ORC
+    }
+
+    /**
+     * The factory method to create KingdomFactory concrete objects.
+     */
+    public static KingdomFactory makeFactory(KingdomType type) {
+      switch (type) {
+        case ELF:
+          return new ElfKingdomFactory();
+        case ORC:
+          return new OrcKingdomFactory();
+        default:
+          throw new IllegalArgumentException("KingdomType not supported.");
+      }
+    }
+  }
+}

abstract-factory/src/main/java/com/iluwatar/abstractfactory/KingdomFactory.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal

abstract-factory/src/main/java/com/iluwatar/abstractfactory/OrcArmy.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -28,7 +28,7 @@ package com.iluwatar.abstractfactory;
  */
 public class OrcArmy implements Army {
 
-  static final String DESCRIPTION = "This is the Orc Army!";
+  static final String DESCRIPTION = "This is the orc army!";
 
   @Override
   public String getDescription() {

abstract-factory/src/main/java/com/iluwatar/abstractfactory/OrcCastle.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -28,7 +28,7 @@ package com.iluwatar.abstractfactory;
  */
 public class OrcCastle implements Castle {
 
-  static final String DESCRIPTION = "This is the Orc castle!";
+  static final String DESCRIPTION = "This is the orc castle!";
 
   @Override
   public String getDescription() {

abstract-factory/src/main/java/com/iluwatar/abstractfactory/OrcKing.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -28,7 +28,7 @@ package com.iluwatar.abstractfactory;
  */
 public class OrcKing implements King {
 
-  static final String DESCRIPTION = "This is the Orc king!";
+  static final String DESCRIPTION = "This is the orc king!";
 
   @Override
   public String getDescription() {

abstract-factory/src/main/java/com/iluwatar/abstractfactory/OrcKingdomFactory.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal

abstract-factory/src/test/java/com/iluwatar/abstractfactory/AbstractFactoryTest.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -23,65 +23,71 @@
 
 package com.iluwatar.abstractfactory;
 
+import org.junit.jupiter.api.Test;
+
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
-import com.iluwatar.abstractfactory.App.FactoryMaker;
-import com.iluwatar.abstractfactory.App.FactoryMaker.KingdomType;
-import org.junit.jupiter.api.BeforeEach;
-import org.junit.jupiter.api.Test;
-
 /**
- * Test for abstract factory.
+ * Tests for abstract factory.
  */
-public class AbstractFactoryTest {
+class AbstractFactoryTest {
 
-  private App app = new App();
-  private KingdomFactory elfFactory;
-  private KingdomFactory orcFactory;
-
-  @BeforeEach
-  public void setUp() {
-    elfFactory = FactoryMaker.makeFactory(KingdomType.ELF);
-    orcFactory = FactoryMaker.makeFactory(KingdomType.ORC);
-  }
+  private final App app = new App();
 
   @Test
-  public void king() {
-    final var elfKing = app.getKing(elfFactory);
+  void verifyKingCreation() {
+    app.createKingdom(Kingdom.FactoryMaker.KingdomType.ELF);
+    final var kingdom = app.getKingdom();
+
+    final var elfKing = kingdom.getKing();
     assertTrue(elfKing instanceof ElfKing);
     assertEquals(ElfKing.DESCRIPTION, elfKing.getDescription());
-    final var orcKing = app.getKing(orcFactory);
+
+    app.createKingdom(Kingdom.FactoryMaker.KingdomType.ORC);
+    final var orcKing = kingdom.getKing();
     assertTrue(orcKing instanceof OrcKing);
     assertEquals(OrcKing.DESCRIPTION, orcKing.getDescription());
   }
 
   @Test
-  public void castle() {
-    final var elfCastle = app.getCastle(elfFactory);
+  void verifyCastleCreation() {
+    app.createKingdom(Kingdom.FactoryMaker.KingdomType.ELF);
+    final var kingdom = app.getKingdom();
+
+    final var elfCastle = kingdom.getCastle();
     assertTrue(elfCastle instanceof ElfCastle);
     assertEquals(ElfCastle.DESCRIPTION, elfCastle.getDescription());
-    final var orcCastle = app.getCastle(orcFactory);
+
+    app.createKingdom(Kingdom.FactoryMaker.KingdomType.ORC);
+    final var orcCastle = kingdom.getCastle();
     assertTrue(orcCastle instanceof OrcCastle);
     assertEquals(OrcCastle.DESCRIPTION, orcCastle.getDescription());
   }
 
   @Test
-  public void army() {
-    final var elfArmy = app.getArmy(elfFactory);
+  void verifyArmyCreation() {
+    app.createKingdom(Kingdom.FactoryMaker.KingdomType.ELF);
+    final var kingdom = app.getKingdom();
+
+    final var elfArmy = kingdom.getArmy();
     assertTrue(elfArmy instanceof ElfArmy);
     assertEquals(ElfArmy.DESCRIPTION, elfArmy.getDescription());
-    final var orcArmy = app.getArmy(orcFactory);
+
+    app.createKingdom(Kingdom.FactoryMaker.KingdomType.ORC);
+    final var orcArmy = kingdom.getArmy();
     assertTrue(orcArmy instanceof OrcArmy);
     assertEquals(OrcArmy.DESCRIPTION, orcArmy.getDescription());
   }
 
   @Test
-  public void createElfKingdom() {
-    app.createKingdom(elfFactory);
-    final var king = app.getKing();
-    final var castle = app.getCastle();
-    final var army = app.getArmy();
+  void verifyElfKingdomCreation() {
+    app.createKingdom(Kingdom.FactoryMaker.KingdomType.ELF);
+    final var kingdom = app.getKingdom();
+
+    final var king = kingdom.getKing();
+    final var castle = kingdom.getCastle();
+    final var army = kingdom.getArmy();
     assertTrue(king instanceof ElfKing);
     assertEquals(ElfKing.DESCRIPTION, king.getDescription());
     assertTrue(castle instanceof ElfCastle);
@@ -91,11 +97,13 @@ public class AbstractFactoryTest {
   }
 
   @Test
-  public void createOrcKingdom() {
-    app.createKingdom(orcFactory);
-    final var king = app.getKing();
-    final var castle = app.getCastle();
-    final var army = app.getArmy();
+  void verifyOrcKingdomCreation() {
+    app.createKingdom(Kingdom.FactoryMaker.KingdomType.ORC);
+    final var kingdom = app.getKingdom();
+
+    final var king = kingdom.getKing();
+    final var castle = kingdom.getCastle();
+    final var army = kingdom.getArmy();
     assertTrue(king instanceof OrcKing);
     assertEquals(OrcKing.DESCRIPTION, king.getDescription());
     assertTrue(castle instanceof OrcCastle);

abstract-factory/src/test/java/com/iluwatar/abstractfactory/AppTest.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -25,12 +25,16 @@ package com.iluwatar.abstractfactory;
 
 import org.junit.jupiter.api.Test;
 
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+
 /**
- * Tests that Abstract Factory example runs without errors.
+ * Check whether the execution of the main method in {@link App} throws an exception.
  */
-public class AppTest {
+class AppTest {
+    
   @Test
-  public void test() {
-    App.main(new String[]{});
+  void shouldExecuteApplicationWithoutException() {
+
+	  assertDoesNotThrow(() -> App.main(new String[]{}));
   }
 }

active-object/README.md

@@ -0,0 +1,130 @@
+---
+layout: pattern
+title: Active Object
+folder: active-object
+permalink: /patterns/active-object/
+categories: Concurrency
+language: en
+tags:
+ - Performance
+---
+
+
+## Intent
+The active object design pattern decouples method execution from method invocation for objects that each reside in their thread of control. The goal is to introduce concurrency, by using asynchronous method invocation, and a scheduler for handling requests.
+
+## Explanation
+
+The class that implements the active object pattern will contain a self-synchronization mechanism without using 'synchronized' methods.
+
+Real-world example
+
+>The Orcs are known for their wildness and untameable soul. It seems like they have their own thread of control based on previous behavior.
+
+To implement a creature that has its own thread of control mechanism and expose its API only and not the execution itself, we can use the Active Object pattern.
+
+
+**Programmatic Example**
+
+```java
+public abstract class ActiveCreature{
+  private final Logger logger = LoggerFactory.getLogger(ActiveCreature.class.getName());
+
+  private BlockingQueue<Runnable> requests;
+  
+  private String name;
+  
+  private Thread thread;
+
+  public ActiveCreature(String name) {
+    this.name = name;
+    this.requests = new LinkedBlockingQueue<Runnable>();
+    thread = new Thread(new Runnable() {
+        @Override
+        public void run() {
+          while (true) {
+            try {
+              requests.take().run();
+            } catch (InterruptedException e) { 
+              logger.error(e.getMessage());
+            }
+          }
+        }
+      }
+    );
+    thread.start();
+  }
+  
+  public void eat() throws InterruptedException {
+    requests.put(new Runnable() {
+        @Override
+        public void run() { 
+          logger.info("{} is eating!",name());
+          logger.info("{} has finished eating!",name());
+        }
+      }
+    );
+  }
+
+  public void roam() throws InterruptedException {
+    requests.put(new Runnable() {
+        @Override
+        public void run() { 
+          logger.info("{} has started to roam the wastelands.",name());
+        }
+      }
+    );
+  }
+  
+  public String name() {
+    return this.name;
+  }
+}
+```
+
+We can see that any class that will extend the ActiveCreature class will have its own thread of control to invoke and execute methods.
+
+For example, the Orc class:
+
+```java
+public class Orc extends ActiveCreature {
+
+  public Orc(String name) {
+    super(name);
+  }
+
+}
+```
+
+Now, we can create multiple creatures such as Orcs, tell them to eat and roam, and they will execute it on their own thread of control:
+
+```java
+  public static void main(String[] args) {  
+    var app = new App();
+    app.run();
+  }
+  
+  @Override
+  public void run() {
+    ActiveCreature creature;
+    try {
+      for (int i = 0;i < creatures;i++) {
+        creature = new Orc(Orc.class.getSimpleName().toString() + i);
+        creature.eat();
+        creature.roam();
+      }
+      Thread.sleep(1000);
+    } catch (InterruptedException e) {
+      logger.error(e.getMessage());
+    }
+    Runtime.getRuntime().exit(1);
+  }
+```
+
+## Class diagram
+
+![alt text](./etc/active-object.urm.png "Active Object class diagram")
+
+## Tutorials
+
+* [Android and Java Concurrency: The Active Object Pattern](https://www.youtube.com/watch?v=Cd8t2u5Qmvc)

active-object/etc/active-object.urm.puml

@@ -0,0 +1,25 @@
+@startuml
+package com.iluwatar.activeobject {
+  abstract class ActiveCreature {
+    - logger : Logger
+    - name : String
+    - requests : BlockingQueue<Runnable>
+    - thread : Thread
+    + ActiveCreature(name : String)
+    + eat()
+    + name() : String
+    + roam()
+  }
+  class App {
+    - creatures : Integer
+    - logger : Logger
+    + App()
+    + main(args : String[]) {static}
+    + run()
+  }
+  class Orc {
+    + Orc(name : String)
+  }
+}
+Orc --|> ActiveCreature 
+@enduml

active-object/pom.xml

@@ -0,0 +1,62 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+
+    The MIT License
+    Copyright © 2014-2021 Ilkka Seppälä
+
+    Permission is hereby granted, free of charge, to any person obtaining a copy
+    of this software and associated documentation files (the "Software"), to deal
+    in the Software without restriction, including without limitation the rights
+    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+    copies of the Software, and to permit persons to whom the Software is
+    furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included in
+    all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+    THE SOFTWARE.
+
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>com.iluwatar</groupId>
+    <artifactId>java-design-patterns</artifactId>
+    <version>1.26.0-SNAPSHOT</version>
+  </parent>
+  <artifactId>active-object</artifactId>
+  <dependencies>
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-engine</artifactId>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+  <build>
+    <plugins>
+      <!-- Maven assembly plugin is invoked with default setting which we have 
+				in parent pom and specifying the class having main method -->
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-assembly-plugin</artifactId>
+        <executions>
+          <execution>
+            <configuration>
+              <archive>
+                <manifest>
+                  <mainClass>com.iluwatar.activeobject.App</mainClass>
+                </manifest>
+              </archive>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
+</project>

active-object/src/main/java/com/iluwatar/activeobject/ActiveCreature.java

@@ -0,0 +1,118 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2021 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.activeobject;
+
+import java.util.concurrent.BlockingQueue;
+import java.util.concurrent.LinkedBlockingQueue;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * ActiveCreature class is the base of the active object example.
+ * @author Noam Greenshtain
+ *
+ */
+public abstract class ActiveCreature {
+  
+  private static final Logger logger = LoggerFactory.getLogger(ActiveCreature.class.getName());
+
+  private BlockingQueue<Runnable> requests;
+  
+  private String name;
+  
+  private Thread thread; // Thread of execution.
+  
+  private int status; // status of the thread of execution.
+
+  /**
+   * Constructor and initialization.
+   */
+  protected ActiveCreature(String name) {
+    this.name = name;
+    this.status = 0;
+    this.requests = new LinkedBlockingQueue<>();
+    thread = new Thread(() -> {
+      boolean infinite = true;
+      while (infinite) {
+        try {
+          requests.take().run();
+        } catch (InterruptedException e) {
+          if (this.status != 0) {
+            logger.error("Thread was interrupted. --> {}", e.getMessage()); 
+          }
+          infinite = false;
+          Thread.currentThread().interrupt();
+        }
+      }
+    });
+    thread.start();
+  }
+
+  /**
+   * Eats the porridge.
+   * @throws InterruptedException due to firing a new Runnable.
+   */
+  public void eat() throws InterruptedException {
+    requests.put(() -> {
+      logger.info("{} is eating!",name());
+      logger.info("{} has finished eating!",name());
+    });
+  }
+
+  /**
+   * Roam the wastelands.
+   * @throws InterruptedException due to firing a new Runnable.
+   */
+  public void roam() throws InterruptedException {
+    requests.put(() ->
+        logger.info("{} has started to roam in the wastelands.",name())
+    );
+  }
+  
+  /**
+   * Returns the name of the creature.
+   * @return the name of the creature.
+   */
+  public String name() {
+    return this.name;
+  }
+  
+  /**
+   * Kills the thread of execution.
+   * @param status of the thread of execution. 0 == OK, the rest is logging an error.
+   */
+  public void kill(int status) {
+    this.status = status;
+    this.thread.interrupt();
+  }
+  
+  /**
+   * Returns the status of the thread of execution.
+   * @return the status of the thread of execution.
+   */
+  public int getStatus() {
+    return this.status;
+  }
+}

active-object/src/main/java/com/iluwatar/activeobject/App.java

@@ -0,0 +1,75 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2021 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.activeobject;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * The Active Object pattern helps to solve synchronization difficulties without using 
+ * 'synchronized' methods. The active object will contain a thread-safe data structure 
+ * (such as BlockingQueue) and use to synchronize method calls by moving the logic of the method
+ * into an invocator(usually a Runnable) and store it in the DSA.
+ * 
+ * <p>In this example, we fire 20 threads to modify a value in the target class.
+ */
+public class App implements Runnable {
+  
+  private static final Logger logger = LoggerFactory.getLogger(App.class.getName());
+  
+  private static final int NUM_CREATURES = 3;
+
+  /**
+   * Program entry point.
+   *
+   * @param args command line arguments.
+   */
+  public static void main(String[] args) {  
+    var app = new App();
+    app.run();
+  }
+  
+  @Override
+  public void run() {
+    List<ActiveCreature> creatures = new ArrayList<>();
+    try {
+      for (int i = 0;i < NUM_CREATURES;i++) {
+        creatures.add(new Orc(Orc.class.getSimpleName() + i));
+        creatures.get(i).eat();
+        creatures.get(i).roam();
+      }
+      Thread.sleep(1000);
+    } catch (InterruptedException e) {
+      logger.error(e.getMessage());
+      Thread.currentThread().interrupt();
+    } finally {
+      for (int i = 0;i < NUM_CREATURES;i++) {
+        creatures.get(i).kill(0);
+      }
+    }
+  }
+}

active-object/src/main/java/com/iluwatar/activeobject/Orc.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -21,15 +21,17 @@
  * THE SOFTWARE.
  */
 
-package com.iluwatar.semaphore;
+package com.iluwatar.activeobject;
 
 /**
- * Lock is an interface for a lock which can be acquired and released.
+ * An implementation of the ActiveCreature class.
+ * @author Noam Greenshtain
+ *
  */
-public interface Lock {
+public class Orc extends ActiveCreature {
 
-  void acquire() throws InterruptedException;
-
-  void release();
+  public Orc(String name) {
+    super(name);
+  }
 
 }

active-object/src/test/java/com/iluwatar/activeobject/ActiveCreatureTest.java

@@ -0,0 +1,42 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2021 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.activeobject;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+class ActiveCreatureTest {
+	
+	@Test
+	void executionTest() throws InterruptedException {
+		ActiveCreature orc = new Orc("orc1");
+		assertEquals("orc1",orc.name());
+		assertEquals(0,orc.getStatus());
+		orc.eat();
+		orc.roam();
+		orc.kill(0);
+	}
+	
+
+}

active-object/src/test/java/com/iluwatar/activeobject/AppTest.java

@@ -0,0 +1,37 @@
+/*
+ * The MIT License
+ * Copyright © 2014-2021 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.iluwatar.activeobject;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+
+import org.junit.jupiter.api.Test;
+
+
+class AppTest {
+
+	  @Test
+	  void shouldExecuteApplicationWithoutException() {
+	    assertDoesNotThrow(() -> App.main(new String[]{}));
+	  }
+}

acyclic-visitor/README.md

@@ -4,36 +4,162 @@ title: Acyclic Visitor
 folder: acyclic-visitor
 permalink: /patterns/acyclic-visitor/
 categories: Behavioral
+language: en
 tags:
- - Java
- - Difficulty-Intermediate
+ - Extensibility
 ---
 
+## Intent
+
+Allow new functions to be added to existing class hierarchies without affecting those hierarchies, and without creating 
+the troublesome dependency cycles that are inherent to the GoF Visitor Pattern.
+
+## Explanation
+
+Real world example
+
+> We have a hierarchy of modem classes. The modems in this hierarchy need to be visited by an external algorithm based 
+> on filtering criteria (is it Unix or DOS compatible modem). 
+
+In plain words
+
+> Acyclic Visitor allows functions to be added to existing class hierarchies without modifying the hierarchies.
+
+[WikiWikiWeb](https://wiki.c2.com/?AcyclicVisitor) says
+
+> The Acyclic Visitor pattern allows new functions to be added to existing class hierarchies without affecting those 
+> hierarchies, and without creating the dependency cycles that are inherent to the GangOfFour VisitorPattern.
+
+**Programmatic Example**
+
+Here's the `Modem` hierarchy.
+
+```java
+public abstract class Modem {
+  public abstract void accept(ModemVisitor modemVisitor);
+}
+
+public class Zoom extends Modem {
+  ...
+  @Override
+  public void accept(ModemVisitor modemVisitor) {
+    if (modemVisitor instanceof ZoomVisitor) {
+      ((ZoomVisitor) modemVisitor).visit(this);
+    } else {
+      LOGGER.info("Only ZoomVisitor is allowed to visit Zoom modem");
+    }
+  }
+}
+
+public class Hayes extends Modem {
+  ...
+  @Override
+  public void accept(ModemVisitor modemVisitor) {
+    if (modemVisitor instanceof HayesVisitor) {
+      ((HayesVisitor) modemVisitor).visit(this);
+    } else {
+      LOGGER.info("Only HayesVisitor is allowed to visit Hayes modem");
+    }
+  }
+}
+```
+
+Next we introduce the `ModemVisitor` hierarchy.
+
+```java
+public interface ModemVisitor {
+}
+
+public interface HayesVisitor extends ModemVisitor {
+  void visit(Hayes hayes);
+}
+
+public interface ZoomVisitor extends ModemVisitor {
+  void visit(Zoom zoom);
+}
+
+public interface AllModemVisitor extends ZoomVisitor, HayesVisitor {
+}
+
+public class ConfigureForDosVisitor implements AllModemVisitor {
+  ...
+  @Override
+  public void visit(Hayes hayes) {
+    LOGGER.info(hayes + " used with Dos configurator.");
+  }
+  @Override
+  public void visit(Zoom zoom) {
+    LOGGER.info(zoom + " used with Dos configurator.");
+  }
+}
+
+public class ConfigureForUnixVisitor implements ZoomVisitor {
+  ...
+  @Override
+  public void visit(Zoom zoom) {
+    LOGGER.info(zoom + " used with Unix configurator.");
+  }
+}
+```
+
+Finally, here are the visitors in action.
+
+```java
+    var conUnix = new ConfigureForUnixVisitor();
+    var conDos = new ConfigureForDosVisitor();
+    var zoom = new Zoom();
+    var hayes = new Hayes();
+    hayes.accept(conDos);
+    zoom.accept(conDos);
+    hayes.accept(conUnix);
+    zoom.accept(conUnix);   
+```
+
+Program output:
+
+```
+    // Hayes modem used with Dos configurator.
+    // Zoom modem used with Dos configurator.
+    // Only HayesVisitor is allowed to visit Hayes modem
+    // Zoom modem used with Unix configurator.
+```
+
+## Class diagram
+
 ![alt text](./etc/acyclic-visitor.png "Acyclic Visitor")
 
-## Intent
-Allow new functions to be added to existing class hierarchies without affecting those hierarchies, and without creating the troublesome dependency cycles that are inherent to the GOF VISITOR Pattern.
-
 ## Applicability
+
 This pattern can be used:
+
 * When you need to add a new function to an existing hierarchy without the need to alter or affect that hierarchy.
 * When there are functions that operate upon a hierarchy, but which do not belong in the hierarchy itself. e.g. the ConfigureForDOS / ConfigureForUnix / ConfigureForX issue.
 * When you need to perform very different operations on an object depending upon its type.
 * When the visited class hierarchy will be frequently extended with new derivatives of the Element class.
 * When the recompilation, relinking, retesting or redistribution of the derivatives of Element is very expensive.
 
+## Tutorial
+
+* [Acyclic Visitor Pattern Example](https://codecrafter.blogspot.com/2012/12/the-acyclic-visitor-pattern.html)
+
 ## Consequences
+
 The good:
+
 * No dependency cycles between class hierarchies.
 * No need to recompile all the visitors if a new one is added.
 * Does not cause compilation failure in existing visitors if class hierarchy has a new member.
 
 The bad:
-* Violates the principle of least surprise or Liskov's Substitution principle by showing that it can accept all visitors but actually only being interested in particular visitors.
+
+* Violates [Liskov's Substitution Principle](https://java-design-patterns.com/principles/#liskov-substitution-principle) by showing that it can accept all visitors but actually only being interested in particular visitors.
 * Parallel hierarchy of visitors has to be created for all members in visitable class hierarchy.
 
 ## Related patterns
-* [Visitor Pattern](../visitor/)
+
+* [Visitor Pattern](https://java-design-patterns.com/patterns/visitor/)
 
 ## Credits
-* [Acyclic Visitor](http://condor.depaul.edu/dmumaugh/OOT/Design-Principles/acv.pdf)
+
+* [Acyclic Visitor by Robert C. Martin](http://condor.depaul.edu/dmumaugh/OOT/Design-Principles/acv.pdf)
+* [Acyclic Visitor in WikiWikiWeb](https://wiki.c2.com/?AcyclicVisitor)

acyclic-visitor/etc/Acyclic Visitor.ucls

@@ -1,115 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<class-diagram version="1.2.2" icons="true" always-add-relationships="false" generalizations="true" realizations="true" 
-  associations="true" dependencies="false" nesting-relationships="true" router="FAN">  
-  <interface id="1" language="java" name="com.iluwatar.acyclicvisitor.ModemVisitor" project="acyclic-visitor" 
-    file="/acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/ModemVisitor.java" binary="false" 
-    corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="860" y="67"/>    
-    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
-      sort-features="false" accessors="true" visibility="true">      
-      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
-      <operations public="true" package="true" protected="true" private="true" static="true"/>    
-    </display>  
-  </interface>  
-  <class id="2" language="java" name="com.iluwatar.acyclicvisitor.Modem" project="acyclic-visitor" 
-    file="/acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/Modem.java" binary="false" corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="327" y="77"/>    
-    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
-      sort-features="false" accessors="true" visibility="true">      
-      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
-      <operations public="true" package="true" protected="true" private="true" static="true"/>    
-    </display>  
-  </class>  
-  <class id="3" language="java" name="com.iluwatar.acyclicvisitor.ConfigureForUnixVisitor" project="acyclic-visitor" 
-    file="/acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/ConfigureForUnixVisitor.java" binary="false" 
-    corner="BOTTOM_RIGHT">    
-    <position height="124" width="196" x="647" y="225"/>    
-    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
-      sort-features="false" accessors="true" visibility="true">      
-      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
-      <operations public="true" package="true" protected="true" private="true" static="true"/>    
-    </display>  
-  </class>  
-  <class id="4" language="java" name="com.iluwatar.acyclicvisitor.Zoom" project="acyclic-visitor" 
-    file="/acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/Zoom.java" binary="false" corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="203" y="305"/>    
-    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
-      sort-features="false" accessors="true" visibility="true">      
-      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
-      <operations public="true" package="true" protected="true" private="true" static="true"/>    
-    </display>  
-  </class>  
-  <interface id="5" language="java" name="com.iluwatar.acyclicvisitor.HayesVisitor" project="acyclic-visitor" 
-    file="/acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/HayesVisitor.java" binary="false" 
-    corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="1019" y="468"/>    
-    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
-      sort-features="false" accessors="true" visibility="true">      
-      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
-      <operations public="true" package="true" protected="true" private="true" static="true"/>    
-    </display>  
-  </interface>  
-  <interface id="6" language="java" name="com.iluwatar.acyclicvisitor.ZoomVisitor" project="acyclic-visitor" 
-    file="/acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/ZoomVisitor.java" binary="false" 
-    corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="758" y="467"/>    
-    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
-      sort-features="false" accessors="true" visibility="true">      
-      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
-      <operations public="true" package="true" protected="true" private="true" static="true"/>    
-    </display>  
-  </interface>  
-  <class id="7" language="java" name="com.iluwatar.acyclicvisitor.Hayes" project="acyclic-visitor" 
-    file="/acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/Hayes.java" binary="false" corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="479" y="307"/>    
-    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
-      sort-features="false" accessors="true" visibility="true">      
-      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
-      <operations public="true" package="true" protected="true" private="true" static="true"/>    
-    </display>  
-  </class>  
-  <class id="8" language="java" name="com.iluwatar.acyclicvisitor.ConfigureForDosVisitor" project="acyclic-visitor" 
-    file="/acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/ConfigureForDosVisitor.java" binary="false" 
-    corner="BOTTOM_RIGHT">    
-    <position height="142" width="192" x="883" y="225"/>    
-    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
-      sort-features="false" accessors="true" visibility="true">      
-      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
-      <operations public="true" package="true" protected="true" private="true" static="true"/>    
-    </display>  
-  </class>  
-  <generalization id="9">    
-    <end type="SOURCE" refId="7"/>    
-    <end type="TARGET" refId="2"/>  
-  </generalization>  
-  <realization id="10">    
-    <end type="SOURCE" refId="8"/>    
-    <end type="TARGET" refId="6"/>  
-  </realization>  
-  <realization id="11">    
-    <end type="SOURCE" refId="8"/>    
-    <end type="TARGET" refId="5"/>  
-  </realization>  
-  <realization id="12">    
-    <end type="SOURCE" refId="3"/>    
-    <end type="TARGET" refId="6"/>  
-  </realization>  
-  <realization id="13">    
-    <end type="SOURCE" refId="3"/>    
-    <end type="TARGET" refId="1"/>  
-  </realization>  
-  <realization id="14">    
-    <end type="SOURCE" refId="8"/>    
-    <end type="TARGET" refId="1"/>  
-  </realization>  
-  <generalization id="15">    
-    <end type="SOURCE" refId="4"/>    
-    <end type="TARGET" refId="2"/>  
-  </generalization>  
-  <classifier-display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
-    sort-features="false" accessors="true" visibility="true">    
-    <attributes public="true" package="true" protected="true" private="true" static="true"/>    
-    <operations public="true" package="true" protected="true" private="true" static="true"/>  
-  </classifier-display>  
-  <association-display labels="true" multiplicity="true"/>
-</class-diagram>

acyclic-visitor/etc/acyclic-visitor.urm.puml

@@ -0,0 +1,53 @@
+@startuml
+package com.iluwatar.acyclicvisitor {
+  interface AllModemVisitor {
+  }
+  class App {
+    + App()
+    + main(args : String[]) {static}
+  }
+  class ConfigureForDosVisitor {
+    - LOGGER : Logger {static}
+    + ConfigureForDosVisitor()
+    + visit(hayes : Hayes)
+    + visit(zoom : Zoom)
+  }
+  class ConfigureForUnixVisitor {
+    - LOGGER : Logger {static}
+    + ConfigureForUnixVisitor()
+    + visit(zoom : Zoom)
+  }
+  class Hayes {
+    - LOGGER : Logger {static}
+    + Hayes()
+    + accept(modemVisitor : ModemVisitor)
+    + toString() : String
+  }
+  interface HayesVisitor {
+    + visit(Hayes) {abstract}
+  }
+  abstract class Modem {
+    + Modem()
+    + accept(ModemVisitor) {abstract}
+  }
+  interface ModemVisitor {
+  }
+  class Zoom {
+    - LOGGER : Logger {static}
+    + Zoom()
+    + accept(modemVisitor : ModemVisitor)
+    + toString() : String
+  }
+  interface ZoomVisitor {
+    + visit(Zoom) {abstract}
+  }
+}
+AllModemVisitor --|> ZoomVisitor 
+AllModemVisitor --|> HayesVisitor 
+ConfigureForDosVisitor ..|> AllModemVisitor 
+ConfigureForUnixVisitor ..|> ZoomVisitor 
+Hayes --|> Modem 
+HayesVisitor --|> ModemVisitor 
+Zoom --|> Modem 
+ZoomVisitor --|> ModemVisitor 
+@enduml

acyclic-visitor/pom.xml

@@ -1,7 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
 <!--
 
     The MIT License
-    Copyright © 2014-2019 Ilkka Seppälä
+    Copyright © 2014-2021 Ilkka Seppälä
 
     Permission is hereby granted, free of charge, to any person obtaining a copy
     of this software and associated documentation files (the "Software"), to deal
@@ -22,50 +23,65 @@
     THE SOFTWARE.
 
 -->
-<project xmlns="http://maven.apache.org/POM/4.0.0"
-	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
-	<modelVersion>4.0.0</modelVersion>
-	
-	<parent>
-		<groupId>com.iluwatar</groupId>
-		<artifactId>java-design-patterns</artifactId>
-		<version>1.22.0-SNAPSHOT</version>
-	</parent>
-	
-	<artifactId>acyclic-visitor</artifactId>
-
-	<properties>
-		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-		<maven.compiler.source>1.8</maven.compiler.source>
-		<maven.compiler.target>1.8</maven.compiler.target>
-	</properties>
-
-	<dependencies>
-		<!-- https://mvnrepository.com/artifact/org.assertj/assertj-core -->
-		<dependency>
-			<groupId>org.assertj</groupId>
-			<artifactId>assertj-core</artifactId>
-			<version>3.9.1</version>
-			<scope>test</scope>
-		</dependency>
-		<!-- https://mvnrepository.com/artifact/uk.org.lidalia/slf4j-test -->
-		<dependency>
-			<groupId>uk.org.lidalia</groupId>
-			<artifactId>slf4j-test</artifactId>
-			<version>1.0.0</version>
-			<scope>test</scope>
-		</dependency>
-    	<dependency>
-      		<groupId>org.junit.jupiter</groupId>
-      		<artifactId>junit-jupiter-engine</artifactId>
-      		<scope>test</scope>
-    	</dependency>
-		<dependency>
-			<groupId>org.mockito</groupId>
-			<artifactId>mockito-all</artifactId>
-			<version>1.9.5</version>
-			<scope>test</scope>
-		</dependency>
-	</dependencies>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>com.iluwatar</groupId>
+    <artifactId>java-design-patterns</artifactId>
+    <version>1.26.0-SNAPSHOT</version>
+  </parent>
+  <artifactId>acyclic-visitor</artifactId>
+  <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    <maven.compiler.source>1.8</maven.compiler.source>
+    <maven.compiler.target>1.8</maven.compiler.target>
+  </properties>
+  <dependencies>
+    <!-- https://mvnrepository.com/artifact/org.assertj/assertj-core -->
+    <dependency>
+      <groupId>org.assertj</groupId>
+      <artifactId>assertj-core</artifactId>
+      <version>3.9.1</version>
+      <scope>test</scope>
+    </dependency>
+    <!-- https://mvnrepository.com/artifact/uk.org.lidalia/slf4j-test -->
+    <dependency>
+      <groupId>uk.org.lidalia</groupId>
+      <artifactId>slf4j-test</artifactId>
+      <version>1.2.0</version>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-engine</artifactId>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.mockito</groupId>
+      <artifactId>mockito-all</artifactId>
+      <version>1.10.19</version>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+  <build>
+    <plugins>
+      <!-- Maven assembly plugin is invoked with default setting which we have 
+        in parent pom and specifying the class having main method -->
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-assembly-plugin</artifactId>
+        <executions>
+          <execution>
+            <configuration>
+              <archive>
+                <manifest>
+                  <mainClass>com.iluwatar.acyclicvisitor.App</mainClass>
+                </manifest>
+              </archive>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
 </project>

acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/AllModemVisitor.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal

acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/App.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal

acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/ConfigureForDosVisitor.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -23,17 +23,15 @@
 
 package com.iluwatar.acyclicvisitor;
 
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
+import lombok.extern.slf4j.Slf4j;
 
 /**
  * ConfigureForDosVisitor class implements both zoom's and  hayes' visit method for Dos
  * manufacturer.
  */
+@Slf4j
 public class ConfigureForDosVisitor implements AllModemVisitor {
 
-  private static final Logger LOGGER = LoggerFactory.getLogger(ConfigureForDosVisitor.class);
-
   @Override
   public void visit(Hayes hayes) {
     LOGGER.info(hayes + " used with Dos configurator.");

acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/ConfigureForUnixVisitor.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -23,17 +23,15 @@
 
 package com.iluwatar.acyclicvisitor;
 
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
+import lombok.extern.slf4j.Slf4j;
 
 /**
  * ConfigureForUnixVisitor class implements zoom's visit method for Unix manufacturer, unlike
  * traditional visitor pattern, this class may selectively implement visit for other modems.
  */
+@Slf4j
 public class ConfigureForUnixVisitor implements ZoomVisitor {
 
-  private static final Logger LOGGER = LoggerFactory.getLogger(ConfigureForUnixVisitor.class);
-
   @Override
   public void visit(Zoom zoom) {
     LOGGER.info(zoom + " used with Unix configurator.");

acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/Hayes.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -23,15 +23,13 @@
 
 package com.iluwatar.acyclicvisitor;
 
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
+import lombok.extern.slf4j.Slf4j;
 
 /**
  * Hayes class implements its accept method.
  */
-public class Hayes extends Modem {
-
-  private static final Logger LOGGER = LoggerFactory.getLogger(ConfigureForDosVisitor.class);
+@Slf4j
+public class Hayes implements Modem {
 
   /**
    * Accepts all visitors but honors only HayesVisitor.

acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/HayesVisitor.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal

acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/Modem.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -24,8 +24,9 @@
 package com.iluwatar.acyclicvisitor;
 
 /**
- * Modem abstract class.
+ * //Modem abstract class.
+ * converted to an interface
  */
-public abstract class Modem {
-  public abstract void accept(ModemVisitor modemVisitor);
+public interface Modem {
+  void accept(ModemVisitor modemVisitor);
 }

acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/ModemVisitor.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal

acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/Zoom.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -23,15 +23,13 @@
 
 package com.iluwatar.acyclicvisitor;
 
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
+import lombok.extern.slf4j.Slf4j;
 
 /**
  * Zoom class implements its accept method.
  */
-public class Zoom extends Modem {
-
-  private static final Logger LOGGER = LoggerFactory.getLogger(ConfigureForDosVisitor.class);
+@Slf4j
+public class Zoom implements Modem {
 
   /**
    * Accepts all visitors but honors only ZoomVisitor.

acyclic-visitor/src/main/java/com/iluwatar/acyclicvisitor/ZoomVisitor.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal

acyclic-visitor/src/test/java/com/iluwatar/acyclicvisitor/AppTest.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -25,13 +25,23 @@ package com.iluwatar.acyclicvisitor;
 
 import org.junit.jupiter.api.Test;
 
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+
 /**
  * Tests that the Acyclic Visitor example runs without errors.
  */
-public class AppTest {
+class AppTest {
+
+  /**
+   * Issue: Add at least one assertion to this test case.
+   *
+   * Solution: Inserted assertion to check whether the execution of the main method in {@link App}
+   * throws an exception.
+   */
 
   @Test
-  public void test() {
-    App.main(new String[]{});
+  void shouldExecuteApplicationWithoutException() {
+
+    assertDoesNotThrow(() -> App.main(new String[]{}));
   }
 }

acyclic-visitor/src/test/java/com/iluwatar/acyclicvisitor/ConfigureForDosVisitorTest.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -35,34 +35,34 @@ import uk.org.lidalia.slf4jtest.TestLoggerFactory;
 /**
  * ConfigureForDosVisitor test class
  */
-public class ConfigureForDosVisitorTest {
+class ConfigureForDosVisitorTest {
+
+  private final TestLogger logger = TestLoggerFactory.getTestLogger(ConfigureForDosVisitor.class);
 
-  private TestLogger logger = TestLoggerFactory.getTestLogger(ConfigureForDosVisitor.class);
-  
   @Test
-  public void testVisitForZoom() {    
+  void testVisitForZoom() {
     var conDos = new ConfigureForDosVisitor();
     var zoom = new Zoom();
-    
+
     conDos.visit(zoom);
-    
+
     assertThat(logger.getLoggingEvents())
         .extracting("level", "message")
         .contains(tuple(INFO, zoom + " used with Dos configurator."));
   }
-  
+
   @Test
-  public void testVisitForHayes() {
+  void testVisitForHayes() {
     var conDos = new ConfigureForDosVisitor();
     var hayes = new Hayes();
-    
+
     conDos.visit(hayes);
-    
+
     assertThat(logger.getLoggingEvents())
         .extracting("level", "message")
         .contains(tuple(INFO, hayes + " used with Dos configurator."));
   }
-  
+
   @AfterEach
   public void clearLoggers() {
     TestLoggerFactory.clear();

acyclic-visitor/src/test/java/com/iluwatar/acyclicvisitor/ConfigureForUnixVisitorTest.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -23,35 +23,34 @@
 
 package com.iluwatar.acyclicvisitor;
 
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.Test;
+import uk.org.lidalia.slf4jtest.TestLogger;
+import uk.org.lidalia.slf4jtest.TestLoggerFactory;
+
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.groups.Tuple.tuple;
 import static uk.org.lidalia.slf4jext.Level.INFO;
 
-import org.junit.jupiter.api.AfterEach;
-import org.junit.jupiter.api.Test;
-
-import uk.org.lidalia.slf4jtest.TestLogger;
-import uk.org.lidalia.slf4jtest.TestLoggerFactory;
-
 /**
  * ConfigureForUnixVisitor test class
  */
-public class ConfigureForUnixVisitorTest {
-  
+class ConfigureForUnixVisitorTest {
+
   private static final TestLogger LOGGER = TestLoggerFactory.getTestLogger(ConfigureForUnixVisitor.class);
-  
+
   @AfterEach
   public void clearLoggers() {
     TestLoggerFactory.clear();
   }
-  
+
   @Test
-  public void testVisitForZoom() {
+  void testVisitForZoom() {
     var conUnix = new ConfigureForUnixVisitor();
     var zoom = new Zoom();
-    
+
     conUnix.visit(zoom);
-    
+
     assertThat(LOGGER.getLoggingEvents())
         .extracting("level", "message")
         .contains(tuple(INFO, zoom + " used with Unix configurator."));

acyclic-visitor/src/test/java/com/iluwatar/acyclicvisitor/HayesTest.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -23,34 +23,32 @@
 
 package com.iluwatar.acyclicvisitor;
 
-import static org.mockito.Matchers.eq;
-import static org.mockito.Mockito.mock;
-import static org.mockito.Mockito.verify;
-import static org.mockito.Mockito.verifyZeroInteractions;
-
 import org.junit.jupiter.api.Test;
 
+import static org.mockito.Matchers.eq;
+import static org.mockito.Mockito.*;
+
 /**
  * Hayes test class
  */
-public class HayesTest {
+class HayesTest {
 
   @Test
-  public void testAcceptForDos() {  
+  void testAcceptForDos() {
     var hayes = new Hayes();
     var mockVisitor = mock(ConfigureForDosVisitor.class);
-    
+
     hayes.accept(mockVisitor);
-    verify((HayesVisitor)mockVisitor).visit(eq(hayes));
+    verify((HayesVisitor) mockVisitor).visit(eq(hayes));
   }
-  
+
   @Test
-  public void testAcceptForUnix() {    
+  void testAcceptForUnix() {
     var hayes = new Hayes();
     var mockVisitor = mock(ConfigureForUnixVisitor.class);
-    
+
     hayes.accept(mockVisitor);
-    
+
     verifyZeroInteractions(mockVisitor);
   }
 }

acyclic-visitor/src/test/java/com/iluwatar/acyclicvisitor/ZoomTest.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -24,32 +24,32 @@
 package com.iluwatar.acyclicvisitor;
 
 
-import static org.mockito.Matchers.eq;
-import static org.mockito.Mockito.verify;
-import static org.mockito.Mockito.mock;
-
 import org.junit.jupiter.api.Test;
 
+import static org.mockito.Matchers.eq;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
+
 /**
  * Zoom test class
  */
-public class ZoomTest {
-  
+class ZoomTest {
+
   @Test
-  public void testAcceptForDos() {  
+  void testAcceptForDos() {
     var zoom = new Zoom();
     var mockVisitor = mock(ConfigureForDosVisitor.class);
-    
+
     zoom.accept(mockVisitor);
-    verify((ZoomVisitor)mockVisitor).visit(eq(zoom));
+    verify((ZoomVisitor) mockVisitor).visit(eq(zoom));
   }
-  
+
   @Test
-  public void testAcceptForUnix() {
+  void testAcceptForUnix() {
     var zoom = new Zoom();
     var mockVisitor = mock(ConfigureForUnixVisitor.class);
-    
+
     zoom.accept(mockVisitor);
-    verify((ZoomVisitor)mockVisitor).visit(eq(zoom));
+    verify((ZoomVisitor) mockVisitor).visit(eq(zoom));
   }
 }

adapter/README.md

@@ -4,26 +4,24 @@ title: Adapter
 folder: adapter
 permalink: /patterns/adapter/
 categories: Structural
+language: en
 tags:
- - Java
- - Gang Of Four
- - Difficulty-Beginner
+ - Gang of Four
 ---
 
 ## Also known as
 Wrapper
 
 ## Intent
-Convert the interface of a class into another interface the clients
-expect. Adapter lets classes work together that couldn't otherwise because of
-incompatible interfaces.
+Convert the interface of a class into another interface the clients expect. Adapter lets classes work together that 
+couldn't otherwise because of incompatible interfaces.
 
 ## Explanation
 
-Real world example
+Real-world example
 
-> Consider that you have some pictures in your memory card and you need to transfer them to your computer. In order to transfer them you need some kind of adapter that is compatible with your computer ports so that you can attach memory card to your computer. In this case card reader is an adapter.
-> Another example would be the famous power adapter; a three legged plug can't be connected to a two pronged outlet, it needs to use a power adapter that makes it compatible with the two pronged outlet.
+> Consider that you have some pictures on your memory card and you need to transfer them to your computer. To transfer them, you need some kind of adapter that is compatible with your computer ports so that you can attach a memory card to your computer. In this case card reader is an adapter.
+> Another example would be the famous power adapter; a three-legged plug can't be connected to a two-pronged outlet, it needs to use a power adapter that makes it compatible with the two-pronged outlets.
 > Yet another example would be a translator translating words spoken by one person to another
 
 In plain words
@@ -38,15 +36,15 @@ Wikipedia says
 
 Consider a captain that can only use rowing boats and cannot sail at all.
 
-First we have interfaces `RowingBoat` and `FishingBoat`
+First, we have interfaces `RowingBoat` and `FishingBoat`
 
 ```java
 public interface RowingBoat {
   void row();
 }
 
+@Slf4j
 public class FishingBoat {
-  private static final Logger LOGGER = LoggerFactory.getLogger(FishingBoat.class);
   public void sail() {
     LOGGER.info("The fishing boat is sailing");
   }
@@ -58,7 +56,7 @@ And captain expects an implementation of `RowingBoat` interface to be able to mo
 ```java
 public class Captain {
 
-  private RowingBoat rowingBoat;
+  private final RowingBoat rowingBoat;
   // default constructor and setter for rowingBoat
   public Captain(RowingBoat rowingBoat) {
     this.rowingBoat = rowingBoat;
@@ -70,14 +68,13 @@ public class Captain {
 }
 ```
 
-Now let's say the pirates are coming and our captain needs to escape but there is only fishing boat available. We need to create an adapter that allows the captain to operate the fishing boat with his rowing boat skills.
+Now let's say the pirates are coming and our captain needs to escape but there is only a fishing boat available. We need to create an adapter that allows the captain to operate the fishing boat with his rowing boat skills.
 
 ```java
+@Slf4j
 public class FishingBoatAdapter implements RowingBoat {
 
-  private static final Logger LOGGER = LoggerFactory.getLogger(FishingBoatAdapter.class);
-
-  private FishingBoat boat;
+  private final FishingBoat boat;
 
   public FishingBoatAdapter() {
     boat = new FishingBoat();
@@ -97,28 +94,37 @@ var captain = new Captain(new FishingBoatAdapter());
 captain.row();
 ```
 
+## Class diagram
+![alt text](./etc/adapter.urm.png "Adapter class diagram")
+
 ## Applicability
 Use the Adapter pattern when
 
-* you want to use an existing class, and its interface does not match the one you need
-* you want to create a reusable class that cooperates with unrelated or unforeseen classes, that is, classes that don't necessarily have compatible interfaces
-* you need to use several existing subclasses, but it's impractical to adapt their interface by subclassing every one. An object adapter can adapt the interface of its parent class.
-* most of the applications using third party libraries use adapters as a middle layer between the application and the 3rd party library to decouple the application from the library. If another library has to be used only an adapter for the new library is required without having to change the application code.
+* You want to use an existing class, and its interface does not match the one you need
+* You want to create a reusable class that cooperates with unrelated or unforeseen classes, that is, classes that don't necessarily have compatible interfaces
+* You need to use several existing subclasses, but it's impractical to adapt their interface by subclassing everyone. An object adapter can adapt the interface of its parent class.
+* Most of the applications using third-party libraries use adapters as a middle layer between the application and the 3rd party library to decouple the application from the library. If another library has to be used only an adapter for the new library is required without having to change the application code.
 
-## Consequences:
+## Tutorials
+
+* [Dzone](https://dzone.com/articles/adapter-design-pattern-in-java)
+* [Refactoring Guru](https://refactoring.guru/design-patterns/adapter/java/example)
+* [Baeldung](https://www.baeldung.com/java-adapter-pattern)
+
+## Consequences
 Class and object adapters have different trade-offs. A class adapter
 
-*	adapts Adaptee to Target by committing to a concrete Adaptee class. As a consequence, a class adapter won’t work when we want to adapt a class and all its subclasses.
-*	let’s Adapter override some of Adaptee’s behavior, since Adapter is a subclass of Adaptee.
-*	introduces only one object, and no additional pointer indirection is needed to get to the adaptee.
+*	Adapts Adaptee to Target by committing to a concrete Adaptee class. As a consequence, a class adapter won’t work when we want to adapt a class and all its subclasses.
+*	Let’s Adapter override some of Adaptee’s behavior since Adapter is a subclass of Adaptee.
+*	Introduces only one object, and no additional pointer indirection is needed to get to the adaptee.
 
 An object adapter	
 
-*	let’s a single Adapter work with many Adaptees—that is, the Adaptee itself and all of its subclasses (if any). The Adapter can also add functionality to all Adaptees at once.
-*	makes it harder to override Adaptee behavior. It will require subclassing Adaptee and making Adapter refer to the subclass rather than the Adaptee itself.
+*	Lets a single Adapter work with many Adaptees—that is, the Adaptee itself and all of its subclasses (if any). The Adapter can also add functionality to all Adaptees at once.
+*	Makes it harder to override Adaptee behavior. It will require subclassing Adaptee and making the Adapter refer to the subclass rather than the Adaptee itself.
 
 
-## Real world examples
+## Real-world examples
 
 * [java.util.Arrays#asList()](http://docs.oracle.com/javase/8/docs/api/java/util/Arrays.html#asList%28T...%29)
 * [java.util.Collections#list()](https://docs.oracle.com/javase/8/docs/api/java/util/Collections.html#list-java.util.Enumeration-)
@@ -128,5 +134,7 @@ An object adapter
 
 ## Credits
 
-* [Design Patterns: Elements of Reusable Object-Oriented Software](http://www.amazon.com/Design-Patterns-Elements-Reusable-Object-Oriented/dp/0201633612)
-* [J2EE Design Patterns](http://www.amazon.com/J2EE-Design-Patterns-William-Crawford/dp/0596004273/ref=sr_1_2)
+* [Design Patterns: Elements of Reusable Object-Oriented Software](https://www.amazon.com/gp/product/0201633612/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0201633612&linkCode=as2&tag=javadesignpat-20&linkId=675d49790ce11db99d90bde47f1aeb59)
+* [J2EE Design Patterns](https://www.amazon.com/gp/product/0596004273/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0596004273&linkCode=as2&tag=javadesignpat-20&linkId=48d37c67fb3d845b802fa9b619ad8f31)
+* [Head First Design Patterns: A Brain-Friendly Guide](https://www.amazon.com/gp/product/0596007124/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0596007124&linkCode=as2&tag=javadesignpat-20&linkId=6b8b6eea86021af6c8e3cd3fc382cb5b)
+* [Refactoring to Patterns](https://www.amazon.com/gp/product/0321213351/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0321213351&linkCode=as2&tag=javadesignpat-20&linkId=2a76fcb387234bc71b1c61150b3cc3a7)

adapter/etc/adapter.urm.puml

@@ -0,0 +1,31 @@
+@startuml
+package com.iluwatar.adapter {
+  class App {
+    - App()
+    + main(args : String[]) {static}
+  }
+  class Captain {
+    - rowingBoat : RowingBoat
+    + Captain()
+    + Captain(boat : RowingBoat)
+    ~ row()
+    ~ setRowingBoat(boat : RowingBoat)
+  }
+  ~class FishingBoat {
+    - LOGGER : Logger {static}
+    ~ FishingBoat()
+    ~ sail()
+  }
+  class FishingBoatAdapter {
+    - boat : FishingBoat
+    + FishingBoatAdapter()
+    + row()
+  }
+  interface RowingBoat {
+    + row() {abstract}
+  }
+}
+FishingBoatAdapter -->  "-boat" FishingBoat
+Captain -->  "-rowingBoat" RowingBoat
+FishingBoatAdapter ..|> RowingBoat 
+@enduml

adapter/pom.xml

@@ -1,8 +1,8 @@
-<?xml version="1.0"?>
+<?xml version="1.0" encoding="UTF-8"?>
 <!--
 
     The MIT License
-    Copyright © 2014-2019 Ilkka Seppälä
+    Copyright © 2014-2021 Ilkka Seppälä
 
     Permission is hereby granted, free of charge, to any person obtaining a copy
     of this software and associated documentation files (the "Software"), to deal
@@ -23,13 +23,12 @@
     THE SOFTWARE.
 
 -->
-<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
-    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
   <modelVersion>4.0.0</modelVersion>
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.22.0-SNAPSHOT</version>
+    <version>1.26.0-SNAPSHOT</version>
   </parent>
   <artifactId>adapter</artifactId>
   <dependencies>
@@ -44,4 +43,25 @@
       <scope>test</scope>
     </dependency>
   </dependencies>
+  <build>
+    <plugins>
+      <!-- Maven assembly plugin is invoked with default setting which we have 
+				in parent pom and specifying the class having main method -->
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-assembly-plugin</artifactId>
+        <executions>
+          <execution>
+            <configuration>
+              <archive>
+                <manifest>
+                  <mainClass>com.iluwatar.adapter.App</mainClass>
+                </manifest>
+              </archive>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
 </project>

adapter/src/main/java/com/iluwatar/adapter/App.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal

adapter/src/main/java/com/iluwatar/adapter/Captain.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -23,24 +23,20 @@
 
 package com.iluwatar.adapter;
 
+import lombok.AllArgsConstructor;
+import lombok.NoArgsConstructor;
+import lombok.Setter;
+
 /**
  * The Captain uses {@link RowingBoat} to sail. <br> This is the client in the pattern.
  */
+@Setter
+@NoArgsConstructor
+@AllArgsConstructor
 public final class Captain {
 
   private RowingBoat rowingBoat;
 
-  public Captain() {
-  }
-
-  public Captain(final RowingBoat boat) {
-    this.rowingBoat = boat;
-  }
-
-  void setRowingBoat(final RowingBoat boat) {
-    this.rowingBoat = boat;
-  }
-
   void row() {
     rowingBoat.row();
   }

adapter/src/main/java/com/iluwatar/adapter/FishingBoat.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -23,18 +23,15 @@
 
 package com.iluwatar.adapter;
 
-import static org.slf4j.LoggerFactory.getLogger;
-
-import org.slf4j.Logger;
+import lombok.extern.slf4j.Slf4j;
 
 /**
  * Device class (adaptee in the pattern). We want to reuse this class. Fishing boat moves by
  * sailing.
  */
+@Slf4j
 final class FishingBoat {
 
-  private static final Logger LOGGER = getLogger(FishingBoat.class);
-
   void sail() {
     LOGGER.info("The fishing boat is sailing");
   }

adapter/src/main/java/com/iluwatar/adapter/FishingBoatAdapter.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -29,11 +29,7 @@ package com.iluwatar.adapter;
  */
 public class FishingBoatAdapter implements RowingBoat {
 
-  private FishingBoat boat;
-
-  public FishingBoatAdapter() {
-    boat = new FishingBoat();
-  }
+  private final FishingBoat boat = new FishingBoat();
 
   public final void row() {
     boat.sail();

adapter/src/main/java/com/iluwatar/adapter/RowingBoat.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal

adapter/src/main/java/com/iluwatar/adapter/package-info.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal

adapter/src/test/java/com/iluwatar/adapter/AdapterPatternTest.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -23,18 +23,19 @@
 
 package com.iluwatar.adapter;
 
-import static org.mockito.Mockito.spy;
-import static org.mockito.Mockito.verify;
-
-import java.util.HashMap;
-import java.util.Map;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
+import java.util.HashMap;
+import java.util.Map;
+
+import static org.mockito.Mockito.spy;
+import static org.mockito.Mockito.verify;
+
 /**
- * Test class
+ * Tests for the adapter pattern.
  */
-public class AdapterPatternTest {
+class AdapterPatternTest {
 
   private Map<String, Object> beans;
 
@@ -64,7 +65,7 @@ public class AdapterPatternTest {
    * by the client ({@link Captain} ).
    */
   @Test
-  public void testAdapter() {
+  void testAdapter() {
     var captain = (Captain) beans.get(ROWING_BEAN);
 
     // when captain moves

adapter/src/test/java/com/iluwatar/adapter/AppTest.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -25,12 +25,21 @@ package com.iluwatar.adapter;
 
 import org.junit.jupiter.api.Test;
 
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+
 /**
  * Tests that Adapter example runs without errors.
  */
-public class AppTest {
+class AppTest {
+
+  /**
+   * Check whether the execution of the main method in {@link App}
+   * throws an exception.
+   */
+
   @Test
-  public void test() {
-    App.main(new String[]{});
+  void shouldExecuteApplicationWithoutException() {
+
+    assertDoesNotThrow(() -> App.main(new String[]{}));
   }
 }

aggregator-microservices/README.md

@@ -4,21 +4,100 @@ title: Aggregator Microservices
 folder: aggregator-microservices
 permalink: /patterns/aggregator-microservices/
 categories: Architectural
+language: en
 tags:
-- Java
-- Spring
+- Cloud distributed
+- Decoupling
+- Microservices
 ---
 
 ## Intent
 
-The user makes a single call to the Aggregator, and the aggregator then calls each relevant microservice and collects
-the data, apply business logic to it, and further publish is as a REST Endpoint.
-More variations of the aggregator are: 
-- Proxy Microservice Design Pattern: A different microservice is called upon the business need. 
-- Chained Microservice Design Pattern: In this case each microservice is dependent/ chained to a series 
-of other microservices.
+The user makes a single call to the aggregator service, and the aggregator then calls each relevant microservice.
 
-![alt text](./etc/aggregator-microservice.png "Aggregator Microservice")
+## Explanation
+
+Real world example
+
+> Our web marketplace needs information about products and their current inventory. It makes a call to an aggregator
+> service which in turn calls the product information microservice and product inventory microservice returning the
+> combined information. 
+
+In plain words
+
+> Aggregator Microservice collects pieces of data from various microservices and returns an aggregate for processing. 
+
+Stack Overflow says
+
+> Aggregator Microservice invokes multiple services to achieve the functionality required by the application.
+
+**Programmatic Example**
+
+Let's start from the data model. Here's our `Product`.
+
+```java
+public class Product {
+  private String title;
+  private int productInventories;
+  // getters and setters ->
+  ...
+}
+```
+
+Next we can introduce our `Aggregator` microservice. It contains clients `ProductInformationClient` and
+`ProductInventoryClient` for calling respective microservices.
+
+```java
+@RestController
+public class Aggregator {
+
+  @Resource
+  private ProductInformationClient informationClient;
+
+  @Resource
+  private ProductInventoryClient inventoryClient;
+
+  @RequestMapping(path = "/product", method = RequestMethod.GET)
+  public Product getProduct() {
+
+    var product = new Product();
+    var productTitle = informationClient.getProductTitle();
+    var productInventory = inventoryClient.getProductInventories();
+
+    //Fallback to error message
+    product.setTitle(requireNonNullElse(productTitle, "Error: Fetching Product Title Failed"));
+
+    //Fallback to default error inventory
+    product.setProductInventories(requireNonNullElse(productInventory, -1));
+
+    return product;
+  }
+}
+```
+
+Here's the essence of information microservice implementation. Inventory microservice is similar, it just returns
+inventory counts.
+
+```java
+@RestController
+public class InformationController {
+  @RequestMapping(value = "/information", method = RequestMethod.GET)
+  public String getProductTitle() {
+    return "The Product Title.";
+  }
+}
+```
+
+Now calling our `Aggregator` REST API returns the product information.
+
+```bash
+curl http://localhost:50004/product
+{"title":"The Product Title.","productInventories":5}
+```
+
+## Class diagram
+
+![alt text](./aggregator-service/etc/aggregator-service.png "Aggregator Microservice")
 
 ## Applicability
 
@@ -26,4 +105,6 @@ Use the Aggregator Microservices pattern when you need a unified API for various
 
 ## Credits
 
-* [Microservice Design Patterns](http://blog.arungupta.me/microservice-design-patterns/)
+* [Microservice Design Patterns](http://web.archive.org/web/20190705163602/http://blog.arungupta.me/microservice-design-patterns/)
+* [Microservices Patterns: With examples in Java](https://www.amazon.com/gp/product/1617294543/ref=as_li_qf_asin_il_tl?ie=UTF8&tag=javadesignpat-20&creative=9325&linkCode=as2&creativeASIN=1617294543&linkId=8b4e570267bc5fb8b8189917b461dc60)
+* [Architectural Patterns: Uncover essential patterns in the most indispensable realm of enterprise architecture](https://www.amazon.com/gp/product/B077T7V8RC/ref=as_li_qf_asin_il_tl?ie=UTF8&tag=javadesignpat-20&creative=9325&linkCode=as2&creativeASIN=B077T7V8RC&linkId=c34d204bfe1b277914b420189f09c1a4)

aggregator-microservices/aggregator-service/etc/aggregator-service.urm.puml

@@ -0,0 +1,43 @@
+@startuml
+package com.iluwatar.aggregator.microservices {
+  class Aggregator {
+    - informationClient : ProductInformationClient
+    - inventoryClient : ProductInventoryClient
+    + Aggregator()
+    + getProduct() : Product
+  }
+  class App {
+    + App()
+    + main(args : String[]) {static}
+  }
+  class Product {
+    - productInventories : int
+    - title : String
+    + Product()
+    + getProductInventories() : int
+    + getTitle() : String
+    + setProductInventories(productInventories : int)
+    + setTitle(title : String)
+  }
+  interface ProductInformationClient {
+    + getProductTitle() : String {abstract}
+  }
+  class ProductInformationClientImpl {
+    - LOGGER : Logger {static}
+    + ProductInformationClientImpl()
+    + getProductTitle() : String
+  }
+  interface ProductInventoryClient {
+    + getProductInventories() : Integer {abstract}
+  }
+  class ProductInventoryClientImpl {
+    - LOGGER : Logger {static}
+    + ProductInventoryClientImpl()
+    + getProductInventories() : Integer
+  }
+}
+Aggregator -->  "-informationClient" ProductInformationClient
+Aggregator -->  "-inventoryClient" ProductInventoryClient
+ProductInformationClientImpl ..|> ProductInformationClient 
+ProductInventoryClientImpl ..|> ProductInventoryClient 
+@enduml

aggregator-microservices/aggregator-service/pom.xml

@@ -2,7 +2,7 @@
 <!--
 
     The MIT License
-    Copyright © 2014-2019 Ilkka Seppälä
+    Copyright © 2014-2021 Ilkka Seppälä
 
     Permission is hereby granted, free of charge, to any person obtaining a copy
     of this software and associated documentation files (the "Software"), to deal
@@ -23,51 +23,65 @@
     THE SOFTWARE.
 
 -->
-<project xmlns="http://maven.apache.org/POM/4.0.0"
-         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
-    <parent>
-        <artifactId>aggregator-microservices</artifactId>
-        <groupId>com.iluwatar</groupId>
-        <version>1.22.0-SNAPSHOT</version>
-    </parent>
-    <modelVersion>4.0.0</modelVersion>
-    <artifactId>aggregator-service</artifactId>
-    <packaging>jar</packaging>
-    <dependencies>
-        <dependency>
-            <groupId>org.springframework</groupId>
-            <artifactId>spring-webmvc</artifactId>
-        </dependency>
-        <dependency>
-            <groupId>org.springframework.boot</groupId>
-            <artifactId>spring-boot-starter-web</artifactId>
-        </dependency>
-        <dependency>
-            <groupId>org.junit.jupiter</groupId>
-            <artifactId>junit-jupiter-engine</artifactId>
-            <scope>test</scope>
-        </dependency>
-        <dependency>
-            <groupId>org.mockito</groupId>
-            <artifactId>mockito-core</artifactId>
-            <scope>test</scope>
-        </dependency>
-    </dependencies>
-
-    <build>
-        <plugins>
-            <plugin>
-                <groupId>org.springframework.boot</groupId>
-                <artifactId>spring-boot-maven-plugin</artifactId>
-                <executions>
-                    <execution>
-                        <goals>
-                            <goal>repackage</goal>
-                        </goals>
-                    </execution>
-                </executions>
-            </plugin>
-        </plugins>
-    </build>
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <parent>
+    <artifactId>aggregator-microservices</artifactId>
+    <groupId>com.iluwatar</groupId>
+    <version>1.26.0-SNAPSHOT</version>
+  </parent>
+  <modelVersion>4.0.0</modelVersion>
+  <artifactId>aggregator-service</artifactId>
+  <packaging>jar</packaging>
+  <dependencies>
+    <dependency>
+      <groupId>org.springframework</groupId>
+      <artifactId>spring-webmvc</artifactId>
+    </dependency>
+    <dependency>
+      <groupId>org.springframework.boot</groupId>
+      <artifactId>spring-boot-starter-web</artifactId>
+    </dependency>
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-engine</artifactId>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.mockito</groupId>
+      <artifactId>mockito-core</artifactId>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+  <build>
+    <plugins>
+      <plugin>
+        <groupId>org.springframework.boot</groupId>
+        <artifactId>spring-boot-maven-plugin</artifactId>
+        <executions>
+          <execution>
+            <goals>
+              <goal>repackage</goal>
+            </goals>
+          </execution>
+        </executions>
+      </plugin>
+      <!-- Maven assembly plugin is invoked with default setting which we have 
+				in parent pom and specifying the class having main method -->
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-assembly-plugin</artifactId>
+        <executions>
+          <execution>
+            <configuration>
+              <archive>
+                <manifest>
+                  <mainClass>com.iluwatar.aggregator.microservices.App</mainClass>
+                </manifest>
+              </archive>
+            </configuration>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
 </project>

aggregator-microservices/aggregator-service/src/main/java/com/iluwatar/aggregator/microservices/Aggregator.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -26,8 +26,7 @@ package com.iluwatar.aggregator.microservices;
 import static java.util.Objects.requireNonNullElse;
 
 import javax.annotation.Resource;
-import org.springframework.web.bind.annotation.RequestMapping;
-import org.springframework.web.bind.annotation.RequestMethod;
+import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.RestController;
 
 /**
@@ -37,20 +36,18 @@ import org.springframework.web.bind.annotation.RestController;
 @RestController
 public class Aggregator {
 
-
   @Resource
   private ProductInformationClient informationClient;
 
   @Resource
   private ProductInventoryClient inventoryClient;
 
-
   /**
    * Retrieves product data.
    *
    * @return a Product.
    */
-  @RequestMapping(path = "/product", method = RequestMethod.GET)
+  @GetMapping("/product")
   public Product getProduct() {
 
     var product = new Product();

aggregator-microservices/aggregator-service/src/main/java/com/iluwatar/aggregator/microservices/App.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal

aggregator-microservices/aggregator-service/src/main/java/com/iluwatar/aggregator/microservices/Product.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -23,9 +23,14 @@
 
 package com.iluwatar.aggregator.microservices;
 
+import lombok.Getter;
+import lombok.Setter;
+
 /**
  * Encapsulates all the data for a Product that clients will request.
  */
+@Getter
+@Setter
 public class Product {
 
   /**
@@ -39,20 +44,4 @@ public class Product {
    */
   private int productInventories;
 
-  public String getTitle() {
-    return title;
-  }
-
-  public void setTitle(String title) {
-    this.title = title;
-  }
-
-  public int getProductInventories() {
-    return productInventories;
-  }
-
-  public void setProductInventories(int productInventories) {
-    this.productInventories = productInventories;
-  }
-
 }

aggregator-microservices/aggregator-service/src/main/java/com/iluwatar/aggregator/microservices/ProductInformationClient.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal

aggregator-microservices/aggregator-service/src/main/java/com/iluwatar/aggregator/microservices/ProductInformationClientImpl.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -28,18 +28,16 @@ import java.net.URI;
 import java.net.http.HttpClient;
 import java.net.http.HttpRequest;
 import java.net.http.HttpResponse;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
+import lombok.extern.slf4j.Slf4j;
 import org.springframework.stereotype.Component;
 
 /**
  * An adapter to communicate with information micro-service.
  */
+@Slf4j
 @Component
 public class ProductInformationClientImpl implements ProductInformationClient {
 
-  private static final Logger LOGGER = LoggerFactory.getLogger(ProductInformationClientImpl.class);
-
   @Override
   public String getProductTitle() {
     var request = HttpRequest.newBuilder()
@@ -54,6 +52,7 @@ public class ProductInformationClientImpl implements ProductInformationClient {
       LOGGER.error("IOException Occurred", ioe);
     } catch (InterruptedException ie) {
       LOGGER.error("InterruptedException Occurred", ie);
+      Thread.currentThread().interrupt();
     }
     return null;
   }

aggregator-microservices/aggregator-service/src/main/java/com/iluwatar/aggregator/microservices/ProductInventoryClient.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal

aggregator-microservices/aggregator-service/src/main/java/com/iluwatar/aggregator/microservices/ProductInventoryClientImpl.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -28,18 +28,16 @@ import java.net.URI;
 import java.net.http.HttpClient;
 import java.net.http.HttpRequest;
 import java.net.http.HttpResponse;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
+import lombok.extern.slf4j.Slf4j;
 import org.springframework.stereotype.Component;
 
 /**
  * An adapter to communicate with inventory micro-service.
  */
+@Slf4j
 @Component
 public class ProductInventoryClientImpl implements ProductInventoryClient {
 
-  private static final Logger LOGGER = LoggerFactory.getLogger(ProductInventoryClientImpl.class);
-
   @Override
   public Integer getProductInventories() {
     var response = "";
@@ -56,6 +54,7 @@ public class ProductInventoryClientImpl implements ProductInventoryClient {
       LOGGER.error("IOException Occurred", ioe);
     } catch (InterruptedException ie) {
       LOGGER.error("InterruptedException Occurred", ie);
+      Thread.currentThread().interrupt();
     }
     if ("".equalsIgnoreCase(response)) {
       return null;

aggregator-microservices/aggregator-service/src/main/resources/application.properties

@@ -1,6 +1,6 @@
 #
 # The MIT License
-# Copyright © 2014-2019 Ilkka Seppälä
+# Copyright © 2014-2021 Ilkka Seppälä
 #
 # Permission is hereby granted, free of charge, to any person obtaining a copy
 # of this software and associated documentation files (the "Software"), to deal
@@ -20,4 +20,5 @@
 # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 # THE SOFTWARE.
 #
+
 server.port=50004

aggregator-microservices/aggregator-service/src/test/java/com/iluwatar/aggregator/microservices/AggregatorTest.java

@@ -1,6 +1,6 @@
 /*
  * The MIT License
- * Copyright © 2014-2019 Ilkka Seppälä
+ * Copyright © 2014-2021 Ilkka Seppälä
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -23,19 +23,19 @@
 
 package com.iluwatar.aggregator.microservices;
 
-import static org.junit.jupiter.api.Assertions.assertEquals;
-import static org.mockito.Mockito.when;
-
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.mockito.InjectMocks;
 import org.mockito.Mock;
 import org.mockito.MockitoAnnotations;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.mockito.Mockito.when;
+
 /**
  * Test Aggregation of domain objects
  */
-public class AggregatorTest {
+class AggregatorTest {
 
   @InjectMocks
   private Aggregator aggregator;
@@ -48,14 +48,14 @@ public class AggregatorTest {
 
   @BeforeEach
   public void setup() {
-    MockitoAnnotations.initMocks(this);
+    MockitoAnnotations.openMocks(this);
   }
 
   /**
    * Tests getting the data for a desktop client
    */
   @Test
-  public void testGetProduct() {
+  void testGetProduct() {
     var title = "The Product Title.";
     var inventories = 5;