docs: fixes for yaml frontmatter

* docs: update README.md [skip ci]

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

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

.all-contributorsrc

@@ -1132,7 +1132,8 @@
       "profile": "http://subho.xyz",
       "contributions": [
         "code",
-        "review"
+        "review",
+        "maintenance"
       ]
     },
     {
@@ -1413,6 +1414,223 @@
       "contributions": [
         "code"
       ]
+    },
+    {
+      "login": "va1m",
+      "name": "va1m",
+      "avatar_url": "https://avatars.githubusercontent.com/u/17025445?v=4",
+      "profile": "https://github.com/va1m",
+      "contributions": [
+        "code"
+      ]
+    },
+    {
+      "login": "noamgrinch",
+      "name": "Noam Greenshtain",
+      "avatar_url": "https://avatars.githubusercontent.com/u/31648669?v=4",
+      "profile": "https://github.com/noamgrinch",
+      "contributions": [
+        "code"
+      ]
+    },
+    {
+      "login": "qfxl",
+      "name": "yonghong Xu",
+      "avatar_url": "https://avatars.githubusercontent.com/u/14086462?v=4",
+      "profile": "https://xuyonghong.cn/",
+      "contributions": [
+        "doc"
+      ]
+    },
+    {
+      "login": "jinishavora",
+      "name": "jinishavora",
+      "avatar_url": "https://avatars.githubusercontent.com/u/40777762?v=4",
+      "profile": "https://www.linkedin.com/in/jinisha-vora",
+      "contributions": [
+        "review",
+        "code"
+      ]
+    },
+    {
+      "login": "eas5",
+      "name": "Elvys Soares",
+      "avatar_url": "https://avatars.githubusercontent.com/u/50836521?v=4",
+      "profile": "https://github.com/eas5",
+      "contributions": [
+        "code"
+      ]
+    },
+    {
+      "login": "zWeBrain",
+      "name": "zWeBrain",
+      "avatar_url": "https://avatars.githubusercontent.com/u/46642512?v=4",
+      "profile": "https://github.com/zWeBrain",
+      "contributions": [
+        "code"
+      ]
+    },
+    {
+      "login": "Al-assad",
+      "name": "余林颖",
+      "avatar_url": "https://avatars.githubusercontent.com/u/22493821?v=4",
+      "profile": "https://al-assad.github.io/notion/",
+      "contributions": [
+        "translation"
+      ]
+    },
+    {
+      "login": "STudio26",
+      "name": "Alain",
+      "avatar_url": "https://avatars.githubusercontent.com/u/6988911?v=4",
+      "profile": "https://github.com/STudio26",
+      "contributions": [
+        "translation"
+      ]
+    },
+    {
+      "login": "DEV-VRUPER",
+      "name": "VR",
+      "avatar_url": "https://avatars.githubusercontent.com/u/30525467?v=4",
+      "profile": "https://github.com/DEV-VRUPER",
+      "contributions": [
+        "doc"
+      ]
+    },
+    {
+      "login": "JackieNim",
+      "name": "JackieNim",
+      "avatar_url": "https://avatars.githubusercontent.com/u/4138836?v=4",
+      "profile": "https://github.com/JackieNim",
+      "contributions": [
+        "code"
+      ]
+    },
+    {
+      "login": "EdisonE3",
+      "name": "EdisonE3",
+      "avatar_url": "https://avatars.githubusercontent.com/u/52118917?v=4",
+      "profile": "https://github.com/EdisonE3",
+      "contributions": [
+        "code"
+      ]
+    },
+    {
+      "login": "tao-sun2",
+      "name": "Tao",
+      "avatar_url": "https://avatars.githubusercontent.com/u/66189688?v=4",
+      "profile": "https://github.com/tao-sun2",
+      "contributions": [
+        "code"
+      ]
+    },
+    {
+      "login": "JuanManuelAbate",
+      "name": "Juan Manuel Abate",
+      "avatar_url": "https://avatars.githubusercontent.com/u/16357060?v=4",
+      "profile": "https://github.com/JuanManuelAbate",
+      "contributions": [
+        "translation"
+      ]
+    },
+    {
+      "login": "Xenilo137",
+      "name": "Xenilo137",
+      "avatar_url": "https://avatars.githubusercontent.com/u/24865069?v=4",
+      "profile": "https://github.com/Xenilo137",
+      "contributions": [
+        "code"
+      ]
+    },
+    {
+      "login": "samuelpsouza",
+      "name": "Samuel Souza",
+      "avatar_url": "https://avatars.githubusercontent.com/u/17254162?v=4",
+      "profile": "https://www.linkedin.com/in/souzasamuel/",
+      "contributions": [
+        "code"
+      ]
+    },
+    {
+      "login": "marlo2222",
+      "name": "Marlo Henrique",
+      "avatar_url": "https://avatars.githubusercontent.com/u/40809563?v=4",
+      "profile": "https://github.com/marlo2222",
+      "contributions": [
+        "translation"
+      ]
+    },
+    {
+      "login": "AndriyPyzh",
+      "name": "AndriyPyzh",
+      "avatar_url": "https://avatars.githubusercontent.com/u/57706635?v=4",
+      "profile": "https://github.com/AndriyPyzh",
+      "contributions": [
+        "code"
+      ]
+    },
+    {
+      "login": "karthikbhat13",
+      "name": "karthikbhat13",
+      "avatar_url": "https://avatars.githubusercontent.com/u/22431014?v=4",
+      "profile": "https://github.com/karthikbhat13",
+      "contributions": [
+        "code"
+      ]
+    },
+    {
+      "login": "mortezaadi",
+      "name": "Morteza Adigozalpour",
+      "avatar_url": "https://avatars.githubusercontent.com/u/1329687?v=4",
+      "profile": "https://github.com/mortezaadi",
+      "contributions": [
+        "code"
+      ]
+    },
+    {
+      "login": "tan31989",
+      "name": "Nagaraj Tantri",
+      "avatar_url": "https://avatars.githubusercontent.com/u/3784194?v=4",
+      "profile": "https://stackoverflow.com/users/308565/nagaraj-tantri",
+      "contributions": [
+        "code"
+      ]
+    },
+    {
+      "login": "frascu",
+      "name": "Francesco Scuccimarri",
+      "avatar_url": "https://avatars.githubusercontent.com/u/7107651?v=4",
+      "profile": "http://scuccimarri.it",
+      "contributions": [
+        "code"
+      ]
+    },
+    {
+      "login": "Conhan93",
+      "name": "Conny Hansson",
+      "avatar_url": "https://avatars.githubusercontent.com/u/71334757?v=4",
+      "profile": "https://github.com/Conhan93",
+      "contributions": [
+        "doc"
+      ]
+    },
+    {
+      "login": "muklasr",
+      "name": "Muklas Rahmanto",
+      "avatar_url": "https://avatars.githubusercontent.com/u/43443753?v=4",
+      "profile": "http://muklasr.medium.com",
+      "contributions": [
+        "translation"
+      ]
+    },
+    {
+      "login": "VxDxK",
+      "name": "Vadim",
+      "avatar_url": "https://avatars.githubusercontent.com/u/38704817?v=4",
+      "profile": "https://github.com/VxDxK",
+      "contributions": [
+        "translation"
+      ]
     }
   ],
   "contributorsPerLine": 4,

.github/workflows/maven-ci.yml

@@ -40,25 +40,26 @@ jobs:
     steps:
 
     - name: Checkout Code
-      uses: actions/checkout@master
+      uses: actions/checkout@v2
       with:
         # Disabling shallow clone for improving relevancy of SonarQube reporting
         fetch-depth: 0
 
     - name: Set up JDK 11
-      uses: actions/setup-java@master
+      uses: actions/setup-java@v2
       with:
         java-version: 11
+        distribution: 'adopt'
 
     - name: Cache SonarCloud packages
-      uses: actions/cache@master
+      uses: actions/cache@v2
       with:
         path: ~/.sonar/cache
         key: ${{ runner.os }}-sonar
         restore-keys: ${{ runner.os }}-sonar
 
     - name: Cache Maven dependencies
-      uses: actions/cache@master
+      uses: actions/cache@v2
       with:
         path: ~/.m2/repository
         key: ${{ runner.os }}-maven-${{ hashFiles('**/pom.xml') }}

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

@@ -38,15 +38,16 @@ jobs:
 
     steps:
     - name: Checkout Code
-      uses: actions/checkout@master
+      uses: actions/checkout@v2
     
     - name: Set up JDK 11
-      uses: actions/setup-java@master
+      uses: actions/setup-java@v2
       with:
         java-version: 11
+        distribution: 'adopt'
     
     - name: Cache Maven Dependecies
-      uses: actions/cache@master
+      uses: actions/cache@v2
       with:
         path: ~/.m2/repository
         key: ${{ runner.os }}-maven-${{ hashFiles('**/pom.xml') }}

LICENSE.md

@@ -1,6 +1,6 @@
 The MIT License (MIT)
 
-Copyright (c) 2014-2021 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

@@ -6,16 +6,16 @@
 
 ![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) 
+[![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)
 <!-- ALL-CONTRIBUTORS-BADGE:START - Do not remove or modify this section -->
-[![All Contributors](https://img.shields.io/badge/all_contributors-155-orange.svg?style=flat-square)](#contributors-)
+[![All Contributors](https://img.shields.io/badge/all_contributors-179-orange.svg?style=flat-square)](#contributors-)
 <!-- ALL-CONTRIBUTORS-BADGE:END -->
 
 <br/>
 
-Read in different language : [![CN](/assets/flags/CN.png)**CN**](/zh/README.md), [![KR](/assets/flags/KR.png)**KR**](/ko/README.md), [![FR](/assets/flags/FR.png)**FR**](/fr/README.md), [![TR](/assets/flags/TR.png)**TR**](/tr/README.md), [![AR](/assets/flags/AR.png)**AR**](/ar/README.md)
+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) 
 
 <br/>
 
@@ -34,7 +34,7 @@ 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 
+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 on how to implement a specific pattern. We use the most
@@ -49,7 +49,7 @@ 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 the
-[available design patterns](https://java-design-patterns.com/patterns/) by any 
+[available design patterns](https://java-design-patterns.com/patterns/) by any
 of the following approaches
 
  - 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).
@@ -61,8 +61,8 @@ in your architectures and have as much fun learning them as we had developing th
 
 # 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
@@ -259,7 +259,7 @@ This project is licensed under the terms of the MIT license.
     <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="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></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>
   </tr>
   <tr>
     <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>
@@ -307,6 +307,42 @@ This project is licensed under the terms of the MIT license.
     <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>
     <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>
+  </tr>
+  <tr>
+    <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>
+  </tr>
+  <tr>
+    <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>
+    <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>
+  </tr>
+  <tr>
+    <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>
+  </tr>
+  <tr>
+    <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>
+    <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>
+  </tr>
+  <tr>
+    <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>
   </tr>
 </table>
 

abstract-document/README.md

@@ -4,6 +4,7 @@ title: Abstract Document
 folder: abstract-document
 permalink: /patterns/abstract-document/
 categories: Structural
+language: en
 tags: 
  - Extensibility
 ---

abstract-document/pom.xml

@@ -30,7 +30,7 @@
 	<parent>
 		<artifactId>java-design-patterns</artifactId>
 		<groupId>com.iluwatar</groupId>
-		<version>1.24.0-SNAPSHOT</version>
+		<version>1.25.0-SNAPSHOT</version>
 	</parent>
 	<artifactId>abstract-document</artifactId>
 	<dependencies>

abstract-factory/README.md

@@ -4,6 +4,7 @@ title: Abstract Factory
 folder: abstract-factory
 permalink: /patterns/abstract-factory/
 categories: Creational
+language: en
 tags:
  - Gang of Four
 ---
@@ -19,9 +20,9 @@ objects without specifying their concrete classes.
 
 ## Explanation
 
-Real world example
+Real-world example
 
-> To create a kingdom we need objects with a 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.
+> 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
 
@@ -33,7 +34,7 @@ Wikipedia says
 
 **Programmatic Example**
 
-Translating the kingdom example above. First of all we have some interfaces and implementation for the objects in the 
+Translating the kingdom example above. First of all, we have some interfaces and implementation for the objects in the 
 kingdom.
 
 ```java
@@ -51,21 +52,21 @@ public interface Army {
 
 // 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;
@@ -76,7 +77,7 @@ public class ElfArmy implements Army {
 
 ```
 
-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 {
@@ -110,7 +111,7 @@ public class OrcKingdomFactory implements KingdomFactory {
 }
 ```
 
-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();
@@ -126,13 +127,13 @@ army.getDescription();
 Program output:
 
 ```java
-This is the Elven castle!
-This is the Elven king!
-This is the Elven Army!
+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 (Army, King, Castle).  
+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
@@ -178,8 +179,8 @@ public static void main(String[] args) {
 
 Use the Abstract Factory pattern when
 
-* The system should be independent of how its products are created, composed and represented
-* The system should be configured with one of multiple families of products
+* 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.
@@ -195,13 +196,13 @@ Example use cases
 * 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.
 * While the pattern is great when creating predefined objects, adding the new ones might be challenging.
-* The code becomes 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.
 
-## Tutorial
+## Tutorials
 
 * [Abstract Factory Pattern Tutorial](https://www.journaldev.com/1418/abstract-factory-design-pattern-in-java) 
 

abstract-factory/pom.xml

@@ -31,7 +31,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>java-design-patterns</artifactId>
-		<version>1.24.0-SNAPSHOT</version>
+		<version>1.25.0-SNAPSHOT</version>
 	</parent>
 	<artifactId>abstract-factory</artifactId>
 	<dependencies>

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

@@ -37,7 +37,7 @@ import lombok.extern.slf4j.Slf4j;
  *
  * <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.
  */
 @Slf4j
 public class App implements Runnable {
@@ -60,13 +60,13 @@ public class App implements Runnable {
 
   @Override
   public void run() {
-    LOGGER.info("Elf Kingdom");
+    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");
+    LOGGER.info("orc kingdom");
     createKingdom(Kingdom.FactoryMaker.KingdomType.ORC);
     LOGGER.info(kingdom.getArmy().getDescription());
     LOGGER.info(kingdom.getCastle().getDescription());

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

@@ -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

@@ -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

@@ -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/OrcArmy.java

@@ -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

@@ -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

@@ -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/test/java/com/iluwatar/abstractfactory/AbstractFactoryTest.java

@@ -29,14 +29,14 @@ import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 /**
- * Test for abstract factory.
+ * Tests for abstract factory.
  */
 class AbstractFactoryTest {
 
   private final App app = new App();
 
   @Test
-  void king() {
+  void verifyKingCreation() {
     app.createKingdom(Kingdom.FactoryMaker.KingdomType.ELF);
     final var kingdom = app.getKingdom();
 
@@ -51,7 +51,7 @@ class AbstractFactoryTest {
   }
 
   @Test
-  void castle() {
+  void verifyCastleCreation() {
     app.createKingdom(Kingdom.FactoryMaker.KingdomType.ELF);
     final var kingdom = app.getKingdom();
 
@@ -66,7 +66,7 @@ class AbstractFactoryTest {
   }
 
   @Test
-  void army() {
+  void verifyArmyCreation() {
     app.createKingdom(Kingdom.FactoryMaker.KingdomType.ELF);
     final var kingdom = app.getKingdom();
 
@@ -81,7 +81,7 @@ class AbstractFactoryTest {
   }
 
   @Test
-  void createElfKingdom() {
+  void verifyElfKingdomCreation() {
     app.createKingdom(Kingdom.FactoryMaker.KingdomType.ELF);
     final var kingdom = app.getKingdom();
 
@@ -97,7 +97,7 @@ class AbstractFactoryTest {
   }
 
   @Test
-  void createOrcKingdom() {
+  void verifyOrcKingdomCreation() {
     app.createKingdom(Kingdom.FactoryMaker.KingdomType.ORC);
     final var kingdom = app.getKingdom();
 

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

@@ -28,20 +28,13 @@ 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.
  */
 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
   void shouldExecuteApplicationWithoutException() {
 
-    assertDoesNotThrow(() -> App.main(new String[]{}));
+	  assertDoesNotThrow(() -> App.main(new String[]{}));
   }
 }

active-object/README.md

@@ -0,0 +1,126 @@
+---
+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")

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 +1,65 @@
+<?xml version="1.0"?>
+<!--
+
+    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
+	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">
+	<modelVersion>4.0.0</modelVersion>
+	<parent>
+		<groupId>com.iluwatar</groupId>
+		<artifactId>java-design-patterns</artifactId>
+		<version>1.25.0-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

@@ -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;
+
+/**
+ * An implementation of the ActiveCreature class.
+ * @author Noam Greenshtain
+ *
+ */
+public class Orc extends ActiveCreature {
+
+  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

@@ -4,6 +4,7 @@ title: Acyclic Visitor
 folder: acyclic-visitor
 permalink: /patterns/acyclic-visitor/
 categories: Behavioral
+language: en
 tags:
  - Extensibility
 ---

acyclic-visitor/pom.xml

@@ -30,7 +30,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>java-design-patterns</artifactId>
-		<version>1.24.0-SNAPSHOT</version>
+		<version>1.25.0-SNAPSHOT</version>
 	</parent>
 
 	<artifactId>acyclic-visitor</artifactId>

adapter/README.md

@@ -4,6 +4,7 @@ title: Adapter
 folder: adapter
 permalink: /patterns/adapter/
 categories: Structural
+language: en
 tags:
  - Gang of Four
 ---
@@ -104,7 +105,7 @@ Use the Adapter pattern when
 * 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.
 
-## Consequences:
+## 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.
@@ -117,7 +118,7 @@ An object adapter
 *	makes it harder to override Adaptee behavior. It will require subclassing Adaptee and making Adapter refer to the subclass rather than the Adaptee itself.
 
 
-## Real world examples
+## Known uses
 
 * [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-)

adapter/pom.xml

@@ -31,7 +31,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>java-design-patterns</artifactId>
-		<version>1.24.0-SNAPSHOT</version>
+		<version>1.25.0-SNAPSHOT</version>
 	</parent>
 	<artifactId>adapter</artifactId>
 	<dependencies>

aggregator-microservices/README.md

@@ -4,6 +4,7 @@ title: Aggregator Microservices
 folder: aggregator-microservices
 permalink: /patterns/aggregator-microservices/
 categories: Architectural
+language: en
 tags:
 - Cloud distributed
 - Decoupling

aggregator-microservices/aggregator-service/pom.xml

@@ -29,7 +29,7 @@
 	<parent>
 		<artifactId>aggregator-microservices</artifactId>
 		<groupId>com.iluwatar</groupId>
-		<version>1.24.0-SNAPSHOT</version>
+		<version>1.25.0-SNAPSHOT</version>
 	</parent>
 	<modelVersion>4.0.0</modelVersion>
 	<artifactId>aggregator-service</artifactId>

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

@@ -48,7 +48,7 @@ class AggregatorTest {
 
   @BeforeEach
   public void setup() {
-    MockitoAnnotations.initMocks(this);
+    MockitoAnnotations.openMocks(this);
   }
 
   /**

aggregator-microservices/information-microservice/pom.xml

@@ -29,7 +29,7 @@
 	<parent>
 		<artifactId>aggregator-microservices</artifactId>
 		<groupId>com.iluwatar</groupId>
-		<version>1.24.0-SNAPSHOT</version>
+		<version>1.25.0-SNAPSHOT</version>
 	</parent>
 	<modelVersion>4.0.0</modelVersion>
 

aggregator-microservices/inventory-microservice/pom.xml

@@ -29,7 +29,7 @@
 	<parent>
 		<artifactId>aggregator-microservices</artifactId>
 		<groupId>com.iluwatar</groupId>
-		<version>1.24.0-SNAPSHOT</version>
+		<version>1.25.0-SNAPSHOT</version>
 	</parent>
 	<modelVersion>4.0.0</modelVersion>
 	<artifactId>inventory-microservice</artifactId>

aggregator-microservices/pom.xml

@@ -29,7 +29,7 @@
     <parent>
         <artifactId>java-design-patterns</artifactId>
         <groupId>com.iluwatar</groupId>
-        <version>1.24.0-SNAPSHOT</version>
+        <version>1.25.0-SNAPSHOT</version>
     </parent>
     <modelVersion>4.0.0</modelVersion>
     <artifactId>aggregator-microservices</artifactId>

ambassador/README.md

@@ -4,6 +4,7 @@ title: Ambassador
 folder: ambassador
 permalink: /patterns/ambassador/
 categories: Structural
+language: en
 tags:
   - Decoupling
   - Cloud distributed

ambassador/pom.xml

@@ -29,7 +29,7 @@
 	<parent>
 		<artifactId>java-design-patterns</artifactId>
 		<groupId>com.iluwatar</groupId>
-		<version>1.24.0-SNAPSHOT</version>
+		<version>1.25.0-SNAPSHOT</version>
 	</parent>
 	<modelVersion>4.0.0</modelVersion>
 	<artifactId>ambassador</artifactId>

api-gateway/README.md

@@ -4,6 +4,7 @@ title: API Gateway
 folder: api-gateway
 permalink: /patterns/api-gateway/
 categories: Architectural
+language: en
 tags:
   - Cloud distributed
   - Decoupling

api-gateway/api-gateway-service/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <artifactId>api-gateway</artifactId>
     <groupId>com.iluwatar</groupId>
-    <version>1.24.0-SNAPSHOT</version>
+    <version>1.25.0-SNAPSHOT</version>
   </parent>
   <modelVersion>4.0.0</modelVersion>
   <artifactId>api-gateway-service</artifactId>

api-gateway/api-gateway-service/src/test/java/com/iluwatar/api/gateway/ApiGatewayTest.java

@@ -48,7 +48,7 @@ class ApiGatewayTest {
 
   @BeforeEach
   public void setup() {
-    MockitoAnnotations.initMocks(this);
+    MockitoAnnotations.openMocks(this);
   }
 
   /**

api-gateway/image-microservice/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <artifactId>api-gateway</artifactId>
     <groupId>com.iluwatar</groupId>
-    <version>1.24.0-SNAPSHOT</version>
+    <version>1.25.0-SNAPSHOT</version>
   </parent>
   <modelVersion>4.0.0</modelVersion>
   <artifactId>image-microservice</artifactId>

api-gateway/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <artifactId>java-design-patterns</artifactId>
     <groupId>com.iluwatar</groupId>
-    <version>1.24.0-SNAPSHOT</version>
+    <version>1.25.0-SNAPSHOT</version>
   </parent>
   <modelVersion>4.0.0</modelVersion>
   <artifactId>api-gateway</artifactId>

api-gateway/price-microservice/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <artifactId>api-gateway</artifactId>
     <groupId>com.iluwatar</groupId>
-    <version>1.24.0-SNAPSHOT</version>
+    <version>1.25.0-SNAPSHOT</version>
   </parent>
 
   <modelVersion>4.0.0</modelVersion>

arrange-act-assert/README.md

@@ -4,6 +4,7 @@ title: Arrange/Act/Assert
 folder: arrange-act-assert
 permalink: /patterns/arrange-act-assert/
 categories: Idiom
+language: en
 tags:
  - Testing
 ---

arrange-act-assert/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <artifactId>java-design-patterns</artifactId>
     <groupId>com.iluwatar</groupId>
-    <version>1.24.0-SNAPSHOT</version>
+    <version>1.25.0-SNAPSHOT</version>
   </parent>
   <modelVersion>4.0.0</modelVersion>
 

async-method-invocation/README.md

@@ -4,26 +4,166 @@ title: Async Method Invocation
 folder: async-method-invocation
 permalink: /patterns/async-method-invocation/
 categories: Concurrency
+language: en
 tags:
  - Reactive
 ---
 
 ## Intent
-Asynchronous method invocation is pattern where the calling thread
+
+Asynchronous method invocation is a pattern where the calling thread
 is not blocked while waiting results of tasks. The pattern provides parallel
 processing of multiple independent tasks and retrieving the results via
 callbacks or waiting until everything is done. 
 
+## Explanation
+
+Real world example
+
+> Launching space rockets is an exciting business. The mission command gives an order to launch and 
+> after some undetermined time, the rocket either launches successfully or fails miserably.
+
+In plain words
+
+> Asynchronous method invocation starts task processing and returns immediately before the task is 
+> ready. The results of the task processing are returned to the caller later.
+
+Wikipedia says
+
+> In multithreaded computer programming, asynchronous method invocation (AMI), also known as 
+> asynchronous method calls or the asynchronous pattern is a design pattern in which the call site 
+> is not blocked while waiting for the called code to finish. Instead, the calling thread is 
+> notified when the reply arrives. Polling for a reply is an undesired option.
+
+**Programmatic Example**
+
+In this example, we are launching space rockets and deploying lunar rovers.
+
+The application demonstrates the async method invocation pattern. The key parts of the pattern are 
+`AsyncResult` which is an intermediate container for an asynchronously evaluated value, 
+`AsyncCallback` which can be provided to be executed on task completion and `AsyncExecutor` that 
+manages the execution of the async tasks.
+
+```java
+public interface AsyncResult<T> {
+  boolean isCompleted();
+  T getValue() throws ExecutionException;
+  void await() throws InterruptedException;
+}
+```
+
+```java
+public interface AsyncCallback<T> {
+  void onComplete(T value, Optional<Exception> ex);
+}
+```
+
+```java
+public interface AsyncExecutor {
+  <T> AsyncResult<T> startProcess(Callable<T> task);
+  <T> AsyncResult<T> startProcess(Callable<T> task, AsyncCallback<T> callback);
+  <T> T endProcess(AsyncResult<T> asyncResult) throws ExecutionException, InterruptedException;
+}
+```
+
+`ThreadAsyncExecutor` is an implementation of `AsyncExecutor`. Some of its key parts are highlighted 
+next.
+
+```java
+public class ThreadAsyncExecutor implements AsyncExecutor {
+
+  @Override
+  public <T> AsyncResult<T> startProcess(Callable<T> task) {
+    return startProcess(task, null);
+  }
+
+  @Override
+  public <T> AsyncResult<T> startProcess(Callable<T> task, AsyncCallback<T> callback) {
+    var result = new CompletableResult<>(callback);
+    new Thread(
+            () -> {
+              try {
+                result.setValue(task.call());
+              } catch (Exception ex) {
+                result.setException(ex);
+              }
+            },
+            "executor-" + idx.incrementAndGet())
+        .start();
+    return result;
+  }
+
+  @Override
+  public <T> T endProcess(AsyncResult<T> asyncResult)
+      throws ExecutionException, InterruptedException {
+    if (!asyncResult.isCompleted()) {
+      asyncResult.await();
+    }
+    return asyncResult.getValue();
+  }
+}
+```
+
+Then we are ready to launch some rockets to see how everything works together.
+
+```java
+public static void main(String[] args) throws Exception {
+  // construct a new executor that will run async tasks
+  var executor = new ThreadAsyncExecutor();
+
+  // start few async tasks with varying processing times, two last with callback handlers
+  final var asyncResult1 = executor.startProcess(lazyval(10, 500));
+  final var asyncResult2 = executor.startProcess(lazyval("test", 300));
+  final var asyncResult3 = executor.startProcess(lazyval(50L, 700));
+  final var asyncResult4 = executor.startProcess(lazyval(20, 400), callback("Deploying lunar rover"));
+  final var asyncResult5 =
+      executor.startProcess(lazyval("callback", 600), callback("Deploying lunar rover"));
+
+  // emulate processing in the current thread while async tasks are running in their own threads
+  Thread.sleep(350); // Oh boy, we are working hard here
+  log("Mission command is sipping coffee");
+
+  // wait for completion of the tasks
+  final var result1 = executor.endProcess(asyncResult1);
+  final var result2 = executor.endProcess(asyncResult2);
+  final var result3 = executor.endProcess(asyncResult3);
+  asyncResult4.await();
+  asyncResult5.await();
+
+  // log the results of the tasks, callbacks log immediately when complete
+  log("Space rocket <" + result1 + "> launch complete");
+  log("Space rocket <" + result2 + "> launch complete");
+  log("Space rocket <" + result3 + "> launch complete");
+}
+```
+
+Here's the program console output.
+
+```java
+21:47:08.227 [executor-2] INFO com.iluwatar.async.method.invocation.App - Space rocket <test> launched successfully
+21:47:08.269 [main] INFO com.iluwatar.async.method.invocation.App - Mission command is sipping coffee
+21:47:08.318 [executor-4] INFO com.iluwatar.async.method.invocation.App - Space rocket <20> launched successfully
+21:47:08.335 [executor-4] INFO com.iluwatar.async.method.invocation.App - Deploying lunar rover <20>
+21:47:08.414 [executor-1] INFO com.iluwatar.async.method.invocation.App - Space rocket <10> launched successfully
+21:47:08.519 [executor-5] INFO com.iluwatar.async.method.invocation.App - Space rocket <callback> launched successfully
+21:47:08.519 [executor-5] INFO com.iluwatar.async.method.invocation.App - Deploying lunar rover <callback>
+21:47:08.616 [executor-3] INFO com.iluwatar.async.method.invocation.App - Space rocket <50> launched successfully
+21:47:08.617 [main] INFO com.iluwatar.async.method.invocation.App - Space rocket <10> launch complete
+21:47:08.617 [main] INFO com.iluwatar.async.method.invocation.App - Space rocket <test> launch complete
+21:47:08.618 [main] INFO com.iluwatar.async.method.invocation.App - Space rocket <50> launch complete
+```
+
 # Class diagram
+
 ![alt text](./etc/async-method-invocation.png "Async Method Invocation")
 
 ## Applicability
-Use async method invocation pattern when
+
+Use the async method invocation pattern when
 
 * You have multiple independent tasks that can run in parallel
 * You need to improve the performance of a group of sequential tasks
-* You have limited amount of processing capacity or long running tasks and the
-  caller should not wait the tasks to be ready
+* You have a limited amount of processing capacity or long-running tasks and the caller should not wait for the tasks to be ready
 
 ## Real world examples
 

async-method-invocation/pom.xml

@@ -31,7 +31,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>java-design-patterns</artifactId>
-		<version>1.24.0-SNAPSHOT</version>
+		<version>1.25.0-SNAPSHOT</version>
 	</parent>
 	<artifactId>async-method-invocation</artifactId>
 	<dependencies>

async-method-invocation/src/main/java/com/iluwatar/async/method/invocation/App.java

@@ -27,10 +27,12 @@ import java.util.concurrent.Callable;
 import lombok.extern.slf4j.Slf4j;
 
 /**
- * This application demonstrates the async method invocation pattern. Key parts of the pattern are
- * <code>AsyncResult</code> which is an intermediate container for an asynchronously evaluated
- * value, <code>AsyncCallback</code> which can be provided to be executed on task completion and
- * <code>AsyncExecutor</code> that manages the execution of the async tasks.
+ * In this example, we are launching space rockets and deploying lunar rovers.
+ *
+ * <p>The application demonstrates the async method invocation pattern. The key parts of the
+ * pattern are <code>AsyncResult</code> which is an intermediate container for an asynchronously
+ * evaluated value, <code>AsyncCallback</code> which can be provided to be executed on task
+ * completion and <code>AsyncExecutor</code> that manages the execution of the async tasks.
  *
  * <p>The main method shows example flow of async invocations. The main thread starts multiple
  * tasks with variable durations and then continues its own work. When the main thread has done it's
@@ -68,13 +70,14 @@ public class App {
     final var asyncResult1 = executor.startProcess(lazyval(10, 500));
     final var asyncResult2 = executor.startProcess(lazyval("test", 300));
     final var asyncResult3 = executor.startProcess(lazyval(50L, 700));
-    final var asyncResult4 = executor.startProcess(lazyval(20, 400), callback("Callback result 4"));
+    final var asyncResult4 = executor.startProcess(lazyval(20, 400),
+        callback("Deploying lunar rover"));
     final var asyncResult5 =
-        executor.startProcess(lazyval("callback", 600), callback("Callback result 5"));
+        executor.startProcess(lazyval("callback", 600), callback("Deploying lunar rover"));
 
     // emulate processing in the current thread while async tasks are running in their own threads
-    Thread.sleep(350); // Oh boy I'm working hard here
-    log("Some hard work done");
+    Thread.sleep(350); // Oh boy, we are working hard here
+    log("Mission command is sipping coffee");
 
     // wait for completion of the tasks
     final var result1 = executor.endProcess(asyncResult1);
@@ -84,9 +87,9 @@ public class App {
     asyncResult5.await();
 
     // log the results of the tasks, callbacks log immediately when complete
-    log("Result 1: " + result1);
-    log("Result 2: " + result2);
-    log("Result 3: " + result3);
+    log("Space rocket <" + result1 + "> launch complete");
+    log("Space rocket <" + result2 + "> launch complete");
+    log("Space rocket <" + result3 + "> launch complete");
   }
 
   /**
@@ -99,7 +102,7 @@ public class App {
   private static <T> Callable<T> lazyval(T value, long delayMillis) {
     return () -> {
       Thread.sleep(delayMillis);
-      log("Task completed with: " + value);
+      log("Space rocket <" + value + "> launched successfully");
       return value;
     };
   }
@@ -115,7 +118,7 @@ public class App {
       if (ex.isPresent()) {
         log(name + " failed: " + ex.map(Exception::getMessage).orElse(""));
       } else {
-        log(name + ": " + value);
+        log(name + " <" + value + ">");
       }
     };
   }

async-method-invocation/src/test/java/com/iluwatar/async/method/invocation/ThreadAsyncExecutorTest.java

@@ -68,7 +68,7 @@ class ThreadAsyncExecutorTest {
 
   @BeforeEach
   void setUp() {
-    MockitoAnnotations.initMocks(this);
+    MockitoAnnotations.openMocks(this);
   }
 
   /**

balking/README.md

@@ -4,24 +4,137 @@ title: Balking
 folder: balking
 permalink: /patterns/balking/
 categories: Concurrency
+language: en
 tags:
  - Decoupling
 ---
 
 ## Intent
-Balking Pattern is used to prevent an object from executing certain code if it is an
-incomplete or inappropriate state
+
+Balking Pattern is used to prevent an object from executing a certain code if it is in an incomplete 
+or inappropriate state.
+
+## Explanation
+
+Real world example
+
+> There's a start-button in a washing machine to initiate the laundry washing. When the washing 
+> machine is inactive the button works as expected, but if it's already washing the button does
+> nothing.
+
+In plain words
+
+> Using the balking pattern, a certain code executes only if the object is in particular state.
+
+Wikipedia says
+
+> The balking pattern is a software design pattern that only executes an action on an object when 
+> the object is in a particular state. For example, if an object reads ZIP files and a calling 
+> method invokes a get method on the object when the ZIP file is not open, the object would "balk" 
+> at the request.
+
+**Programmatic Example**
+
+In this example implementation, `WashingMachine` is an object that has two states in which it can 
+be: ENABLED and WASHING. If the machine is ENABLED, the state changes to WASHING using a thread-safe
+method. On the other hand, if it already has been washing and any other thread executes `wash()` 
+it won't do that and returns without doing anything.
+
+Here are the relevant parts of the `WashingMachine` class.
+
+```java
+@Slf4j
+public class WashingMachine {
+
+  private final DelayProvider delayProvider;
+  private WashingMachineState washingMachineState;
+
+  public WashingMachine(DelayProvider delayProvider) {
+    this.delayProvider = delayProvider;
+    this.washingMachineState = WashingMachineState.ENABLED;
+  }
+
+  public WashingMachineState getWashingMachineState() {
+    return washingMachineState;
+  }
+
+  public void wash() {
+    synchronized (this) {
+      var machineState = getWashingMachineState();
+      LOGGER.info("{}: Actual machine state: {}", Thread.currentThread().getName(), machineState);
+      if (this.washingMachineState == WashingMachineState.WASHING) {
+        LOGGER.error("Cannot wash if the machine has been already washing!");
+        return;
+      }
+      this.washingMachineState = WashingMachineState.WASHING;
+    }
+    LOGGER.info("{}: Doing the washing", Thread.currentThread().getName());
+    this.delayProvider.executeAfterDelay(50, TimeUnit.MILLISECONDS, this::endOfWashing);
+  }
+
+  public synchronized void endOfWashing() {
+    washingMachineState = WashingMachineState.ENABLED;
+    LOGGER.info("{}: Washing completed.", Thread.currentThread().getId());
+  }
+}
+```
+
+Here's the simple `DelayProvider` interface used by the `WashingMachine`.
+
+```java
+public interface DelayProvider {
+  void executeAfterDelay(long interval, TimeUnit timeUnit, Runnable task);
+}
+```
+
+Now we introduce the application using the `WashingMachine`.
+
+```java
+  public static void main(String... args) {
+    final var washingMachine = new WashingMachine();
+    var executorService = Executors.newFixedThreadPool(3);
+    for (int i = 0; i < 3; i++) {
+      executorService.execute(washingMachine::wash);
+    }
+    executorService.shutdown();
+    try {
+      executorService.awaitTermination(10, TimeUnit.SECONDS);
+    } catch (InterruptedException ie) {
+      LOGGER.error("ERROR: Waiting on executor service shutdown!");
+      Thread.currentThread().interrupt();
+    }
+  }
+```
+
+Here is the console output of the program.
+
+```
+14:02:52.268 [pool-1-thread-2] INFO com.iluwatar.balking.WashingMachine - pool-1-thread-2: Actual machine state: ENABLED
+14:02:52.272 [pool-1-thread-2] INFO com.iluwatar.balking.WashingMachine - pool-1-thread-2: Doing the washing
+14:02:52.272 [pool-1-thread-3] INFO com.iluwatar.balking.WashingMachine - pool-1-thread-3: Actual machine state: WASHING
+14:02:52.273 [pool-1-thread-3] ERROR com.iluwatar.balking.WashingMachine - Cannot wash if the machine has been already washing!
+14:02:52.273 [pool-1-thread-1] INFO com.iluwatar.balking.WashingMachine - pool-1-thread-1: Actual machine state: WASHING
+14:02:52.273 [pool-1-thread-1] ERROR com.iluwatar.balking.WashingMachine - Cannot wash if the machine has been already washing!
+14:02:52.324 [pool-1-thread-2] INFO com.iluwatar.balking.WashingMachine - 14: Washing completed.
+```
 
 ## Class diagram
+
 ![alt text](./etc/balking.png "Balking")
 
 ## Applicability
+
 Use the Balking pattern when
 
-* you want to invoke an action on an object only when it is in a particular state
-* objects are generally only in a state that is prone to balking temporarily
-but for an unknown amount of time
+* You want to invoke an action on an object only when it is in a particular state
+* Objects are generally only in a state that is prone to balking temporarily but for an unknown 
+  amount of time
 
 ## Related patterns
-* Guarded Suspension Pattern
-* Double Checked Locking Pattern
+
+* [Guarded Suspension Pattern](https://java-design-patterns.com/patterns/guarded-suspension/)
+* [Double Checked Locking Pattern](https://java-design-patterns.com/patterns/double-checked-locking/)
+
+## Credits
+
+* [Patterns in Java: A Catalog of Reusable Design Patterns Illustrated with UML, 2nd Edition, Volume 1](https://www.amazon.com/gp/product/0471227293/ref=as_li_qf_asin_il_tl?ie=UTF8&tag=javadesignpat-20&creative=9325&linkCode=as2&creativeASIN=0471227293&linkId=0e39a59ffaab93fb476036fecb637b99)

balking/pom.xml

@@ -29,7 +29,7 @@
 	<parent>
 		<artifactId>java-design-patterns</artifactId>
 		<groupId>com.iluwatar</groupId>
-		<version>1.24.0-SNAPSHOT</version>
+		<version>1.25.0-SNAPSHOT</version>
 	</parent>
 	<modelVersion>4.0.0</modelVersion>
 

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

@@ -32,11 +32,11 @@ import lombok.extern.slf4j.Slf4j;
  * then the method will return without doing anything. Objects that use this pattern are generally
  * only in a state that is prone to balking temporarily but for an unknown amount of time
  *
- * <p>In this example implementation WashingMachine is an object that has two states in which it
- * can be: ENABLED and WASHING. If the machine is ENABLED the state is changed into WASHING that any
- * other thread can't invoke this action on this and then do the job. On the other hand if it have
- * been already washing and any other thread execute wash() it can't do that once again and returns
- * doing nothing.
+ * <p>In this example implementation, {@link WashingMachine} is an object that has two states in
+ * which it can be: ENABLED and WASHING. If the machine is ENABLED, the state changes to WASHING
+ * using a thread-safe method. On the other hand, if it already has been washing and any other
+ * thread executes {@link WashingMachine#wash()} it won't do that and returns without doing
+ * anything.
  */
 @Slf4j
 public class App {
@@ -54,11 +54,12 @@ public class App {
     }
     executorService.shutdown();
     try {
-      executorService.awaitTermination(10, TimeUnit.SECONDS);
+      if (!executorService.awaitTermination(10, TimeUnit.SECONDS)) {
+        executorService.shutdownNow();
+      }
     } catch (InterruptedException ie) {
       LOGGER.error("ERROR: Waiting on executor service shutdown!");
       Thread.currentThread().interrupt();
     }
   }
-
 }

bridge/README.md

@@ -4,6 +4,7 @@ title: Bridge
 folder: bridge
 permalink: /patterns/bridge/
 categories: Structural
+language: en
 tags:
  - Gang of Four
 ---
@@ -18,7 +19,7 @@ Decouple an abstraction from its implementation so that the two can vary indepen
 
 ## Explanation
 
-Real world example
+Real-world example
 
 > Consider you have a weapon with different enchantments, and you are supposed to allow mixing 
 > different weapons with different enchantments. What would you do? Create multiple copies of each 
@@ -160,27 +161,36 @@ public class SoulEatingEnchantment implements Enchantment {
 Here are both hierarchies in action:
 
 ```java
+LOGGER.info("The knight receives an enchanted sword.");
 var enchantedSword = new Sword(new SoulEatingEnchantment());
 enchantedSword.wield();
 enchantedSword.swing();
 enchantedSword.unwield();
-// The sword is wielded.
-// The item spreads bloodlust.
-// The sword is swinged.
-// The item eats the soul of enemies.
-// The sword is unwielded.
-// Bloodlust slowly disappears.
 
+LOGGER.info("The valkyrie receives an enchanted hammer.");
 var hammer = new Hammer(new FlyingEnchantment());
 hammer.wield();
 hammer.swing();
 hammer.unwield();
-// The hammer is wielded.
-// The item begins to glow faintly.
-// The hammer is swinged.
-// The item flies and strikes the enemies finally returning to owner's hand.
-// The hammer is unwielded.
-// The item's glow fades.
+```
+
+Here's the console output.
+
+```
+The knight receives an enchanted sword.
+The sword is wielded.
+The item spreads bloodlust.
+The sword is swung.
+The item eats the soul of enemies.
+The sword is unwielded.
+Bloodlust slowly disappears.
+The valkyrie receives an enchanted hammer.
+The hammer is wielded.
+The item begins to glow faintly.
+The hammer is swung.
+The item flies and strikes the enemies finally returning to owner's hand.
+The hammer is unwielded.
+The item's glow fades.
 ```
 
 ## Class diagram

bridge/pom.xml

@@ -31,7 +31,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>java-design-patterns</artifactId>
-		<version>1.24.0-SNAPSHOT</version>
+		<version>1.25.0-SNAPSHOT</version>
 	</parent>
 	<artifactId>bridge</artifactId>
 	<dependencies>

bridge/src/main/java/com/iluwatar/bridge/Hammer.java

@@ -43,7 +43,7 @@ public class Hammer implements Weapon {
 
   @Override
   public void swing() {
-    LOGGER.info("The hammer is swinged.");
+    LOGGER.info("The hammer is swung.");
     enchantment.apply();
   }
 

bridge/src/main/java/com/iluwatar/bridge/Sword.java

@@ -43,7 +43,7 @@ public class Sword implements Weapon {
 
   @Override
   public void swing() {
-    LOGGER.info("The sword is swinged.");
+    LOGGER.info("The sword is swung.");
     enchantment.apply();
   }
 

builder/README.md

@@ -4,6 +4,7 @@ title: Builder
 folder: builder
 permalink: /patterns/builder/
 categories: Creational
+language: en
 tags:
  - Gang of Four
 ---
@@ -15,11 +16,11 @@ process can create different representations.
 
 ## Explanation
 
-Real world example
+Real-world example
 
 > Imagine a character generator for a role-playing game. The easiest option is to let the computer 
 > create the character for you. If you want to manually select the character details like 
-> profession, gender, hair color etc. the character generation becomes a step-by-step process that 
+> profession, gender, hair color, etc. the character generation becomes a step-by-step process that 
 > completes when all the selections are ready.
 
 In plain words
@@ -48,7 +49,7 @@ anti-pattern.
 
 **Programmatic Example**
 
-The sane alternative is to use the Builder pattern. First of all we have our hero that we want to 
+The sane alternative is to use the Builder pattern. First of all, we have our hero that we want to 
 create:
 
 ```java
@@ -133,7 +134,7 @@ Use the Builder pattern when
 * The algorithm for creating a complex object should be independent of the parts that make up the object and how they're assembled
 * The construction process must allow different representations for the object that's constructed
 
-## Real world examples
+## Known uses
 
 * [java.lang.StringBuilder](http://docs.oracle.com/javase/8/docs/api/java/lang/StringBuilder.html)
 * [java.nio.ByteBuffer](http://docs.oracle.com/javase/8/docs/api/java/nio/ByteBuffer.html#put-byte-) as well as similar buffers such as FloatBuffer, IntBuffer and so on.

builder/pom.xml

@@ -31,7 +31,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>java-design-patterns</artifactId>
-		<version>1.24.0-SNAPSHOT</version>
+		<version>1.25.0-SNAPSHOT</version>
 	</parent>
 	<artifactId>builder</artifactId>
 	<dependencies>

business-delegate/README.md

@@ -4,26 +4,162 @@ title: Business Delegate
 folder: business-delegate
 permalink: /patterns/business-delegate/
 categories: Structural
+language: en
 tags:
  - Decoupling
 ---
 
 ## Intent
+
 The Business Delegate pattern adds an abstraction layer between
 presentation and business tiers. By using the pattern we gain loose coupling
 between the tiers and encapsulate knowledge about how to locate, connect to,
 and interact with the business objects that make up the application.
 
+## Explanation
+
+Real world example
+
+> A mobile phone application promises to stream any movie in existence to your phone. It captures
+> the user's search string and passes this on to the business delegate. The business delegate
+> selects the most suitable video streaming service and plays the video from there.
+
+In Plain Words
+
+> Business delegate adds an abstraction layer between the presentation and business tiers.
+
+Wikipedia says
+
+> Business delegate is a Java EE design pattern. This pattern is directing to reduce the coupling 
+> in between business services and the connected presentation tier, and to hide the implementation 
+> details of services (including lookup and accessibility of EJB architecture). Business delegates 
+> acts as an adaptor to invoke business objects from the presentation tier.
+
+**Programmatic Example**
+
+First, we have an abstraction for video streaming services and a couple of implementations.
+
+```java
+public interface VideoStreamingService {
+  void doProcessing();
+}
+
+@Slf4j
+public class NetflixService implements VideoStreamingService {
+  @Override
+  public void doProcessing() {
+    LOGGER.info("NetflixService is now processing");
+  }
+}
+
+@Slf4j
+public class YouTubeService implements VideoStreamingService {
+  @Override
+  public void doProcessing() {
+    LOGGER.info("YouTubeService is now processing");
+  }
+}
+```
+
+Then we have a lookup service that decides which video streaming service is used.
+
+```java
+@Setter
+public class BusinessLookup {
+
+  private NetflixService netflixService;
+  private YouTubeService youTubeService;
+
+  public VideoStreamingService getBusinessService(String movie) {
+    if (movie.toLowerCase(Locale.ROOT).contains("die hard")) {
+      return netflixService;
+    } else {
+      return youTubeService;
+    }
+  }
+}
+```
+
+The business delegate uses a business lookup to route movie playback requests to a suitable
+video streaming service.
+
+```java
+@Setter
+public class BusinessDelegate {
+
+  private BusinessLookup lookupService;
+
+  public void playbackMovie(String movie) {
+    VideoStreamingService videoStreamingService = lookupService.getBusinessService(movie);
+    videoStreamingService.doProcessing();
+  }
+}
+```
+
+The mobile client utilizes business delegate to call the business tier.
+
+```java
+public class MobileClient {
+
+  private final BusinessDelegate businessDelegate;
+
+  public MobileClient(BusinessDelegate businessDelegate) {
+    this.businessDelegate = businessDelegate;
+  }
+
+  public void playbackMovie(String movie) {
+    businessDelegate.playbackMovie(movie);
+  }
+}
+```
+
+Finally, we can show the full example in action.
+
+```java
+  public static void main(String[] args) {
+
+    // prepare the objects
+    var businessDelegate = new BusinessDelegate();
+    var businessLookup = new BusinessLookup();
+    businessLookup.setNetflixService(new NetflixService());
+    businessLookup.setYouTubeService(new YouTubeService());
+    businessDelegate.setLookupService(businessLookup);
+
+    // create the client and use the business delegate
+    var client = new MobileClient(businessDelegate);
+    client.playbackMovie("Die Hard 2");
+    client.playbackMovie("Maradona: The Greatest Ever");
+  }
+```
+
+Here is the console output.
+
+```
+21:15:33.790 [main] INFO com.iluwatar.business.delegate.NetflixService - NetflixService is now processing
+21:15:33.794 [main] INFO com.iluwatar.business.delegate.YouTubeService - YouTubeService is now processing
+```
+
 ## Class diagram
-![alt text](./etc/business-delegate.png "Business Delegate")
+
+![alt text](./etc/business-delegate.urm.png "Business Delegate")
+
+## Related patterns
+
+* [Service locator pattern](https://java-design-patterns.com/patterns/service-locator/)
 
 ## Applicability
+
 Use the Business Delegate pattern when
 
-* you want loose coupling between presentation and business tiers
-* you want to orchestrate calls to multiple business services
-* you want to encapsulate service lookups and service calls
+* You want loose coupling between presentation and business tiers
+* You want to orchestrate calls to multiple business services
+* You want to encapsulate service lookups and service calls
+
+## Tutorials
+
+* [Business Delegate Pattern at TutorialsPoint](https://www.tutorialspoint.com/design_pattern/business_delegate_pattern.htm)
 
 ## Credits
 
 * [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)
+* [Core J2EE Patterns: Best Practices and Design Strategies](https://www.amazon.com/gp/product/0130648841/ref=as_li_qf_asin_il_tl?ie=UTF8&tag=javadesignpat-20&creative=9325&linkCode=as2&creativeASIN=0130648841&linkId=a0100de2b28c71ede8db1757fb2b5947)

business-delegate/etc/business-delegate.ucls

@@ -1,136 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<class-diagram version="1.1.8" icons="true" automaticImage="PNG" always-add-relationships="false" generalizations="true" 
-  realizations="true" associations="true" dependencies="false" nesting-relationships="true">  
-  <class id="1" language="java" name="com.iluwatar.business.delegate.BusinessDelegate" project="business-delegate" 
-    file="/business-delegate/src/main/java/com/iluwatar/business/delegate/BusinessDelegate.java" binary="false" 
-    corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="272" y="219"/>    
-    <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="2" language="java" name="com.iluwatar.business.delegate.Client" project="business-delegate" 
-    file="/business-delegate/src/main/java/com/iluwatar/business/delegate/Client.java" binary="false" 
-    corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="272" y="64"/>    
-    <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>  
-  <enumeration id="3" language="java" name="com.iluwatar.business.delegate.ServiceType" project="business-delegate" 
-    file="/business-delegate/src/main/java/com/iluwatar/business/delegate/ServiceType.java" binary="false" 
-    corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="89" y="383"/>    
-    <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>  
-  </enumeration>  
-  <interface id="4" language="java" name="com.iluwatar.business.delegate.BusinessService" project="business-delegate" 
-    file="/business-delegate/src/main/java/com/iluwatar/business/delegate/BusinessService.java" binary="false" 
-    corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="630" y="365"/>    
-    <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="5" language="java" name="com.iluwatar.business.delegate.JmsService" project="business-delegate" 
-    file="/business-delegate/src/main/java/com/iluwatar/business/delegate/JmsService.java" binary="false" 
-    corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="489" y="210"/>    
-    <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="6" language="java" name="com.iluwatar.business.delegate.BusinessLookup" project="business-delegate" 
-    file="/business-delegate/src/main/java/com/iluwatar/business/delegate/BusinessLookup.java" binary="false" 
-    corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="360" y="399"/>    
-    <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="7" language="java" name="com.iluwatar.business.delegate.EjbService" project="business-delegate" 
-    file="/business-delegate/src/main/java/com/iluwatar/business/delegate/EjbService.java" binary="false" 
-    corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="668" y="210"/>    
-    <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>  
-  <realization id="8">    
-    <end type="SOURCE" refId="7"/>    
-    <end type="TARGET" refId="4"/>  
-  </realization>  
-  <association id="9">    
-    <end type="SOURCE" refId="1" navigable="false">      
-      <attribute id="10" name="lookupService">        
-        <position height="0" width="0" x="0" y="0"/>      
-      </attribute>      
-      <multiplicity id="11" minimum="0" maximum="1">        
-        <position height="0" width="0" x="0" y="0"/>      
-      </multiplicity>    
-    </end>    
-    <end type="TARGET" refId="6" navigable="true"/>    
-    <display labels="true" multiplicity="true"/>  
-  </association>  
-  <association id="12">    
-    <end type="SOURCE" refId="1" navigable="false">      
-      <attribute id="13" name="serviceType">        
-        <position height="0" width="0" x="0" y="0"/>      
-      </attribute>      
-      <multiplicity id="14" minimum="0" maximum="1">        
-        <position height="0" width="0" x="0" y="0"/>      
-      </multiplicity>    
-    </end>    
-    <end type="TARGET" refId="3" navigable="true"/>    
-    <display labels="true" multiplicity="true"/>  
-  </association>  
-  <realization id="15">    
-    <end type="SOURCE" refId="5"/>    
-    <end type="TARGET" refId="4"/>  
-  </realization>  
-  <association id="16">    
-    <end type="SOURCE" refId="2" navigable="false">      
-      <attribute id="17" name="businessDelegate">        
-        <position height="0" width="0" x="0" y="0"/>      
-      </attribute>      
-      <multiplicity id="18" minimum="0" maximum="1">        
-        <position height="0" width="0" x="0" y="0"/>      
-      </multiplicity>    
-    </end>    
-    <end type="TARGET" refId="1" navigable="true"/>    
-    <display labels="true" multiplicity="true"/>  
-  </association>  
-  <association id="19">    
-    <end type="SOURCE" refId="1" navigable="false">      
-      <attribute id="20" name="businessService">        
-        <position height="0" width="0" x="0" y="0"/>      
-      </attribute>      
-      <multiplicity id="21" minimum="0" maximum="1">        
-        <position height="0" width="0" x="0" y="0"/>      
-      </multiplicity>    
-    </end>    
-    <end type="TARGET" refId="4" navigable="true"/>    
-    <display labels="true" multiplicity="true"/>  
-  </association>  
-  <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>

business-delegate/etc/business-delegate.urm.puml

@@ -5,53 +5,42 @@ package com.iluwatar.business.delegate {
     + main(args : String[]) {static}
   }
   class BusinessDelegate {
-    - businessService : BusinessService
     - lookupService : BusinessLookup
-    - serviceType : ServiceType
     + BusinessDelegate()
-    + doTask()
-    + setLookupService(businessLookup : BusinessLookup)
-    + setServiceType(serviceType : ServiceType)
+    + playbackMovie(movie : String)
+    + setLookupService(lookupService : BusinessLookup)
   }
   class BusinessLookup {
-    - ejbService : EjbService
-    - jmsService : JmsService
+    - netflixService : NetflixService
+    - youTubeService : YouTubeService
     + BusinessLookup()
-    + getBusinessService(serviceType : ServiceType) : BusinessService
-    + setEjbService(ejbService : EjbService)
-    + setJmsService(jmsService : JmsService)
+    + getBusinessService(movie : String) : VideoStreamingService
+    + setNetflixService(netflixService : NetflixService)
+    + setYouTubeService(youTubeService : YouTubeService)
   }
-  interface BusinessService {
+  class MobileClient {
+    - businessDelegate : BusinessDelegate
+    + MobileClient(businessDelegate : BusinessDelegate)
+    + playbackMovie(movie : String)
+  }
+  class NetflixService {
+    - LOGGER : Logger {static}
+    + NetflixService()
+    + doProcessing()
+  }
+  interface VideoStreamingService {
     + doProcessing() {abstract}
   }
-  class Client {
-    - businessDelegate : BusinessDelegate
-    + Client(businessDelegate : BusinessDelegate)
-    + doTask()
-  }
-  class EjbService {
+  class YouTubeService {
     - LOGGER : Logger {static}
-    + EjbService()
+    + YouTubeService()
     + doProcessing()
   }
-  class JmsService {
-    - LOGGER : Logger {static}
-    + JmsService()
-    + doProcessing()
-  }
-  enum ServiceType {
-    + EJB {static}
-    + JMS {static}
-    + valueOf(name : String) : ServiceType {static}
-    + values() : ServiceType[] {static}
-  }
 }
-BusinessLookup -->  "-ejbService" EjbService
-BusinessDelegate -->  "-serviceType" ServiceType
-Client -->  "-businessDelegate" BusinessDelegate
-BusinessDelegate -->  "-businessService" BusinessService
+BusinessLookup -->  "-netflixService" NetflixService
+BusinessLookup -->  "-youTubeService" YouTubeService
+MobileClient -->  "-businessDelegate" BusinessDelegate
 BusinessDelegate -->  "-lookupService" BusinessLookup
-BusinessLookup -->  "-jmsService" JmsService
-EjbService ..|> BusinessService 
-JmsService ..|> BusinessService 
+NetflixService ..|> VideoStreamingService 
+YouTubeService ..|> VideoStreamingService 
 @enduml

business-delegate/pom.xml

@@ -31,7 +31,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>java-design-patterns</artifactId>
-		<version>1.24.0-SNAPSHOT</version>
+		<version>1.25.0-SNAPSHOT</version>
 	</parent>
 	<artifactId>business-delegate</artifactId>
 	<dependencies>

business-delegate/src/main/java/com/iluwatar/business/delegate/App.java

@@ -33,9 +33,9 @@ package com.iluwatar.business.delegate;
  * retrieved through service lookups. The Business Delegate itself may contain business logic too
  * potentially tying together multiple service calls, exception handling, retrying etc.
  *
- * <p>In this example the client ({@link Client}) utilizes a business delegate (
- * {@link BusinessDelegate}) to execute a task. The Business Delegate then selects the appropriate
- * service and makes the service call.
+ * <p>In this example the client ({@link MobileClient}) utilizes a business delegate (
+ * {@link BusinessDelegate}) to search for movies in video streaming services. The Business Delegate
+ * then selects the appropriate service and makes the service call.
  */
 public class App {
 
@@ -46,18 +46,16 @@ public class App {
    */
   public static void main(String[] args) {
 
+    // prepare the objects
     var businessDelegate = new BusinessDelegate();
     var businessLookup = new BusinessLookup();
-    businessLookup.setEjbService(new EjbService());
-    businessLookup.setJmsService(new JmsService());
-
+    businessLookup.setNetflixService(new NetflixService());
+    businessLookup.setYouTubeService(new YouTubeService());
     businessDelegate.setLookupService(businessLookup);
-    businessDelegate.setServiceType(ServiceType.EJB);
 
-    var client = new Client(businessDelegate);
-    client.doTask();
-
-    businessDelegate.setServiceType(ServiceType.JMS);
-    client.doTask();
+    // create the client and use the business delegate
+    var client = new MobileClient(businessDelegate);
+    client.playbackMovie("Die Hard 2");
+    client.playbackMovie("Maradona: The Greatest Ever");
   }
 }

business-delegate/src/main/java/com/iluwatar/business/delegate/BusinessDelegate.java

@@ -23,24 +23,18 @@
 
 package com.iluwatar.business.delegate;
 
+import lombok.Setter;
+
 /**
  * BusinessDelegate separates the presentation and business tiers.
  */
+@Setter
 public class BusinessDelegate {
 
   private BusinessLookup lookupService;
-  private ServiceType serviceType;
 
-  public void setLookupService(BusinessLookup businessLookup) {
-    this.lookupService = businessLookup;
-  }
-
-  public void setServiceType(ServiceType serviceType) {
-    this.serviceType = serviceType;
-  }
-
-  public void doTask() {
-    BusinessService businessService = lookupService.getBusinessService(serviceType);
-    businessService.doProcessing();
+  public void playbackMovie(String movie) {
+    VideoStreamingService videoStreamingService = lookupService.getBusinessService(movie);
+    videoStreamingService.doProcessing();
   }
 }

business-delegate/src/main/java/com/iluwatar/business/delegate/BusinessLookup.java

@@ -23,6 +23,7 @@
 
 package com.iluwatar.business.delegate;
 
+import java.util.Locale;
 import lombok.Setter;
 
 /**
@@ -31,21 +32,21 @@ import lombok.Setter;
 @Setter
 public class BusinessLookup {
 
-  private EjbService ejbService;
+  private NetflixService netflixService;
 
-  private JmsService jmsService;
+  private YouTubeService youTubeService;
 
   /**
-   * Gets service instance based on service type.
+   * Gets service instance based on given movie search string.
    *
-   * @param serviceType Type of service instance to be returned.
+   * @param movie Search string for the movie.
    * @return Service instance.
    */
-  public BusinessService getBusinessService(ServiceType serviceType) {
-    if (serviceType.equals(ServiceType.EJB)) {
-      return ejbService;
+  public VideoStreamingService getBusinessService(String movie) {
+    if (movie.toLowerCase(Locale.ROOT).contains("die hard")) {
+      return netflixService;
     } else {
-      return jmsService;
+      return youTubeService;
     }
   }
 }

business-delegate/src/main/java/com/iluwatar/business/delegate/MobileClient.java

@@ -24,17 +24,17 @@
 package com.iluwatar.business.delegate;
 
 /**
- * Client utilizes BusinessDelegate to call the business tier.
+ * MobileClient utilizes BusinessDelegate to call the business tier.
  */
-public class Client {
+public class MobileClient {
 
   private final BusinessDelegate businessDelegate;
 
-  public Client(BusinessDelegate businessDelegate) {
+  public MobileClient(BusinessDelegate businessDelegate) {
     this.businessDelegate = businessDelegate;
   }
 
-  public void doTask() {
-    businessDelegate.doTask();
+  public void playbackMovie(String movie) {
+    businessDelegate.playbackMovie(movie);
   }
 }

business-delegate/src/main/java/com/iluwatar/business/delegate/NetflixService.java

@@ -26,13 +26,13 @@ package com.iluwatar.business.delegate;
 import lombok.extern.slf4j.Slf4j;
 
 /**
- * Service EJB implementation.
+ * NetflixService implementation.
  */
 @Slf4j
-public class EjbService implements BusinessService {
+public class NetflixService implements VideoStreamingService {
 
   @Override
   public void doProcessing() {
-    LOGGER.info("EjbService is now processing");
+    LOGGER.info("NetflixService is now processing");
   }
 }

business-delegate/src/main/java/com/iluwatar/business/delegate/VideoStreamingService.java

@@ -24,9 +24,9 @@
 package com.iluwatar.business.delegate;
 
 /**
- * Interface for service implementations.
+ * Interface for video streaming service implementations.
  */
-public interface BusinessService {
+public interface VideoStreamingService {
 
   void doProcessing();
 }

business-delegate/src/main/java/com/iluwatar/business/delegate/YouTubeService.java

@@ -26,13 +26,13 @@ package com.iluwatar.business.delegate;
 import lombok.extern.slf4j.Slf4j;
 
 /**
- * Service JMS implementation.
+ * YouTubeService implementation.
  */
 @Slf4j
-public class JmsService implements BusinessService {
+public class YouTubeService implements VideoStreamingService {
 
   @Override
   public void doProcessing() {
-    LOGGER.info("JmsService is now processing");
+    LOGGER.info("YouTubeService is now processing");
   }
 }

business-delegate/src/test/java/com/iluwatar/business/delegate/BusinessDelegateTest.java

@@ -26,25 +26,20 @@ package com.iluwatar.business.delegate;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
+
+import static org.mockito.ArgumentMatchers.anyString;
 import static org.mockito.Mockito.spy;
 import static org.mockito.Mockito.times;
 import static org.mockito.Mockito.verify;
 
 /**
- * The Business Delegate pattern adds an abstraction layer between the presentation and business
- * tiers. By using the pattern we gain loose coupling between the tiers. The Business Delegate
- * encapsulates knowledge about how to locate, connect to, and interact with the business objects
- * that make up the application.
- *
- * <p>Some of the services the Business Delegate uses are instantiated directly, and some can be
- * retrieved through service lookups. The Business Delegate itself may contain business logic too
- * potentially tying together multiple service calls, exception handling, retrying etc.
+ * Tests for the {@link BusinessDelegate}
  */
 class BusinessDelegateTest {
 
-  private EjbService ejbService;
+  private NetflixService netflixService;
 
-  private JmsService jmsService;
+  private YouTubeService youTubeService;
 
   private BusinessDelegate businessDelegate;
 
@@ -54,19 +49,19 @@ class BusinessDelegateTest {
    */
   @BeforeEach
   public void setup() {
-    ejbService = spy(new EjbService());
-    jmsService = spy(new JmsService());
+    netflixService = spy(new NetflixService());
+    youTubeService = spy(new YouTubeService());
 
     BusinessLookup businessLookup = spy(new BusinessLookup());
-    businessLookup.setEjbService(ejbService);
-    businessLookup.setJmsService(jmsService);
+    businessLookup.setNetflixService(netflixService);
+    businessLookup.setYouTubeService(youTubeService);
 
     businessDelegate = spy(new BusinessDelegate());
     businessDelegate.setLookupService(businessLookup);
   }
 
   /**
-   * In this example the client ({@link Client}) utilizes a business delegate (
+   * In this example the client ({@link MobileClient}) utilizes a business delegate (
    * {@link BusinessDelegate}) to execute a task. The Business Delegate then selects the appropriate
    * service and makes the service call.
    */
@@ -74,26 +69,20 @@ class BusinessDelegateTest {
   void testBusinessDelegate() {
 
     // setup a client object
-    var client = new Client(businessDelegate);
-
-    // set the service type
-    businessDelegate.setServiceType(ServiceType.EJB);
+    var client = new MobileClient(businessDelegate);
 
     // action
-    client.doTask();
+    client.playbackMovie("Die hard");
 
-    // verifying that the businessDelegate was used by client during doTask() method.
-    verify(businessDelegate).doTask();
-    verify(ejbService).doProcessing();
-
-    // set the service type
-    businessDelegate.setServiceType(ServiceType.JMS);
+    // verifying that the businessDelegate was used by client during playbackMovie() method.
+    verify(businessDelegate).playbackMovie(anyString());
+    verify(netflixService).doProcessing();
 
     // action
-    client.doTask();
+    client.playbackMovie("Maradona");
 
     // verifying that the businessDelegate was used by client during doTask() method.
-    verify(businessDelegate, times(2)).doTask();
-    verify(jmsService).doProcessing();
+    verify(businessDelegate, times(2)).playbackMovie(anyString());
+    verify(youTubeService).doProcessing();
   }
 }

bytecode/README.md

@@ -4,23 +4,240 @@ title: Bytecode
 folder: bytecode
 permalink: /patterns/bytecode/
 categories: Behavioral
+language: en
 tags:
  - Game programming
 ---
 
 ## Intent
-Allows to encode behaviour as instructions for virtual machine.
+
+Allows encoding behavior as instructions for a virtual machine.
+
+## Explanation
+
+Real world example
+
+> A team is working on a new game where wizards battle against each other. The wizard behavior 
+> needs to be carefully adjusted and iterated hundreds of times through playtesting. It's not 
+> optimal to ask the programmer to make changes each time the game designer wants to vary the 
+> behavior, so the wizard behavior is implemented as a data-driven virtual machine.
+
+In plain words
+
+> Bytecode pattern enables behavior driven by data instead of code.
+
+[Gameprogrammingpatterns.com](https://gameprogrammingpatterns.com/bytecode.html) documentation 
+states:
+
+> An instruction set defines the low-level operations that can be performed. A series of 
+> instructions is encoded as a sequence of bytes. A virtual machine executes these instructions one 
+> at a time, using a stack for intermediate values. By combining instructions, complex high-level 
+> behavior can be defined.
+
+**Programmatic Example**
+
+One of the most important game objects is the `Wizard` class.
+
+```java
+@AllArgsConstructor
+@Setter
+@Getter
+@Slf4j
+public class Wizard {
+
+  private int health;
+  private int agility;
+  private int wisdom;
+  private int numberOfPlayedSounds;
+  private int numberOfSpawnedParticles;
+
+  public void playSound() {
+    LOGGER.info("Playing sound");
+    numberOfPlayedSounds++;
+  }
+
+  public void spawnParticles() {
+    LOGGER.info("Spawning particles");
+    numberOfSpawnedParticles++;
+  }
+}
+```
+
+Next, we show the available instructions for our virtual machine. Each of the instructions has its 
+own semantics on how it operates with the stack data. For example, the ADD instruction takes the top
+two items from the stack, adds them together and pushes the result to the stack.
+
+```java
+@AllArgsConstructor
+@Getter
+public enum Instruction {
+
+  LITERAL(1),         // e.g. "LITERAL 0", push 0 to stack
+  SET_HEALTH(2),      // e.g. "SET_HEALTH", pop health and wizard number, call set health
+  SET_WISDOM(3),      // e.g. "SET_WISDOM", pop wisdom and wizard number, call set wisdom
+  SET_AGILITY(4),     // e.g. "SET_AGILITY", pop agility and wizard number, call set agility
+  PLAY_SOUND(5),      // e.g. "PLAY_SOUND", pop value as wizard number, call play sound
+  SPAWN_PARTICLES(6), // e.g. "SPAWN_PARTICLES", pop value as wizard number, call spawn particles
+  GET_HEALTH(7),      // e.g. "GET_HEALTH", pop value as wizard number, push wizard's health
+  GET_AGILITY(8),     // e.g. "GET_AGILITY", pop value as wizard number, push wizard's agility
+  GET_WISDOM(9),      // e.g. "GET_WISDOM", pop value as wizard number, push wizard's wisdom
+  ADD(10),            // e.g. "ADD", pop 2 values, push their sum
+  DIVIDE(11);         // e.g. "DIVIDE", pop 2 values, push their division
+  // ...
+}
+```
+
+At the heart of our example is the `VirtualMachine` class. It takes instructions as input and
+executes them to provide the game object behavior.
+
+```java
+@Getter
+@Slf4j
+public class VirtualMachine {
+
+  private final Stack<Integer> stack = new Stack<>();
+
+  private final Wizard[] wizards = new Wizard[2];
+
+  public VirtualMachine() {
+    wizards[0] = new Wizard(randomInt(3, 32), randomInt(3, 32), randomInt(3, 32),
+        0, 0);
+    wizards[1] = new Wizard(randomInt(3, 32), randomInt(3, 32), randomInt(3, 32),
+        0, 0);
+  }
+
+  public VirtualMachine(Wizard wizard1, Wizard wizard2) {
+    wizards[0] = wizard1;
+    wizards[1] = wizard2;
+  }
+
+  public void execute(int[] bytecode) {
+    for (var i = 0; i < bytecode.length; i++) {
+      Instruction instruction = Instruction.getInstruction(bytecode[i]);
+      switch (instruction) {
+        case LITERAL:
+          // Read the next byte from the bytecode.
+          int value = bytecode[++i];
+          // Push the next value to stack
+          stack.push(value);
+          break;
+        case SET_AGILITY:
+          var amount = stack.pop();
+          var wizard = stack.pop();
+          setAgility(wizard, amount);
+          break;
+        case SET_WISDOM:
+          amount = stack.pop();
+          wizard = stack.pop();
+          setWisdom(wizard, amount);
+          break;
+        case SET_HEALTH:
+          amount = stack.pop();
+          wizard = stack.pop();
+          setHealth(wizard, amount);
+          break;
+        case GET_HEALTH:
+          wizard = stack.pop();
+          stack.push(getHealth(wizard));
+          break;
+        case GET_AGILITY:
+          wizard = stack.pop();
+          stack.push(getAgility(wizard));
+          break;
+        case GET_WISDOM:
+          wizard = stack.pop();
+          stack.push(getWisdom(wizard));
+          break;
+        case ADD:
+          var a = stack.pop();
+          var b = stack.pop();
+          stack.push(a + b);
+          break;
+        case DIVIDE:
+          a = stack.pop();
+          b = stack.pop();
+          stack.push(b / a);
+          break;
+        case PLAY_SOUND:
+          wizard = stack.pop();
+          getWizards()[wizard].playSound();
+          break;
+        case SPAWN_PARTICLES:
+          wizard = stack.pop();
+          getWizards()[wizard].spawnParticles();
+          break;
+        default:
+          throw new IllegalArgumentException("Invalid instruction value");
+      }
+      LOGGER.info("Executed " + instruction.name() + ", Stack contains " + getStack());
+    }
+  }
+
+  public void setHealth(int wizard, int amount) {
+    wizards[wizard].setHealth(amount);
+  }
+  // other setters ->
+  // ...
+}
+```
+
+Now we can show the full example utilizing the virtual machine.
+
+```java
+  public static void main(String[] args) {
+
+    var vm = new VirtualMachine(
+        new Wizard(45, 7, 11, 0, 0),
+        new Wizard(36, 18, 8, 0, 0));
+
+    vm.execute(InstructionConverterUtil.convertToByteCode("LITERAL 0"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("LITERAL 0"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("GET_HEALTH"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("LITERAL 0"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("GET_AGILITY"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("LITERAL 0"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("GET_WISDOM"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("ADD"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("LITERAL 2"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("DIVIDE"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("ADD"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("SET_HEALTH"));
+  }
+```
+
+Here is the console output.
+
+```
+16:20:10.193 [main] INFO com.iluwatar.bytecode.VirtualMachine - Executed LITERAL, Stack contains [0]
+16:20:10.196 [main] INFO com.iluwatar.bytecode.VirtualMachine - Executed LITERAL, Stack contains [0, 0]
+16:20:10.197 [main] INFO com.iluwatar.bytecode.VirtualMachine - Executed GET_HEALTH, Stack contains [0, 45]
+16:20:10.197 [main] INFO com.iluwatar.bytecode.VirtualMachine - Executed LITERAL, Stack contains [0, 45, 0]
+16:20:10.197 [main] INFO com.iluwatar.bytecode.VirtualMachine - Executed GET_AGILITY, Stack contains [0, 45, 7]
+16:20:10.197 [main] INFO com.iluwatar.bytecode.VirtualMachine - Executed LITERAL, Stack contains [0, 45, 7, 0]
+16:20:10.197 [main] INFO com.iluwatar.bytecode.VirtualMachine - Executed GET_WISDOM, Stack contains [0, 45, 7, 11]
+16:20:10.197 [main] INFO com.iluwatar.bytecode.VirtualMachine - Executed ADD, Stack contains [0, 45, 18]
+16:20:10.197 [main] INFO com.iluwatar.bytecode.VirtualMachine - Executed LITERAL, Stack contains [0, 45, 18, 2]
+16:20:10.198 [main] INFO com.iluwatar.bytecode.VirtualMachine - Executed DIVIDE, Stack contains [0, 45, 9]
+16:20:10.198 [main] INFO com.iluwatar.bytecode.VirtualMachine - Executed ADD, Stack contains [0, 54]
+16:20:10.198 [main] INFO com.iluwatar.bytecode.VirtualMachine - Executed SET_HEALTH, Stack contains []
+```
 
 ## Class diagram
+
 ![alt text](./etc/bytecode.urm.png "Bytecode class diagram")
 
 ## Applicability
+
 Use the Bytecode pattern when you have a lot of behavior you need to define and your
 game’s implementation language isn’t a good fit because:
 
-* it’s too low-level, making it tedious or error-prone to program in.
-* iterating on it takes too long due to slow compile times or other tooling issues.
-* it has too much trust. If you want to ensure the behavior being defined can’t break the game, you need to sandbox it from the rest of the codebase.
+* It’s too low-level, making it tedious or error-prone to program in.
+* Iterating on it takes too long due to slow compile times or other tooling issues.
+* It has too much trust. If you want to ensure the behavior being defined can’t break the game, you need to sandbox it from the rest of the codebase.
+
+## Related patterns
+
+* [Interpreter](https://java-design-patterns.com/patterns/interpreter/)
 
 ## Credits
 

bytecode/etc/bytecode.ucls

@@ -1,49 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<class-diagram version="1.2.3" icons="true" always-add-relationships="false" generalizations="true" realizations="true" 
-  associations="true" dependencies="false" nesting-relationships="true" router="FAN">  
-  <class id="1" language="java" name="com.iluwatar.bytecode.VirtualMachine" project="bytecode" 
-    file="/bytecode/src/main/java/com/iluwatar/bytecode/VirtualMachine.java" binary="false" corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="455" y="173"/>    
-    <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="2" language="java" name="com.iluwatar.bytecode.App" project="bytecode" 
-    file="/bytecode/src/main/java/com/iluwatar/bytecode/App.java" binary="false" corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="148" y="110"/>    
-    <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.bytecode.Wizard" project="bytecode" 
-    file="/bytecode/src/main/java/com/iluwatar/bytecode/Wizard.java" binary="false" corner="BOTTOM_RIGHT">    
-    <position height="-1" width="-1" x="148" y="416"/>    
-    <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>  
-  <association id="4">    
-    <end type="SOURCE" refId="1" navigable="false" variant="ASSOCIATION">      
-      <attribute id="5" name="wizards">        
-        <position height="18" width="48" x="296" y="291"/>      
-      </attribute>      
-      <multiplicity id="6" minimum="0" maximum="2147483647">        
-        <position height="0" width="0" x="-327" y="-27"/>      
-      </multiplicity>    
-    </end>    
-    <end type="TARGET" refId="3" navigable="true" variant="ASSOCIATION"/>    
-    <display labels="true" multiplicity="true"/>  
-  </association>  
-  <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>

bytecode/etc/bytecode.urm.puml

@@ -3,7 +3,6 @@ package com.iluwatar.bytecode {
   class App {
     - LOGGER : Logger {static}
     + App()
-    - interpretInstruction(instruction : String, vm : VirtualMachine) {static}
     + main(args : String[]) {static}
   }
   enum Instruction {
@@ -18,22 +17,25 @@ package com.iluwatar.bytecode {
     + SET_HEALTH {static}
     + SET_WISDOM {static}
     + SPAWN_PARTICLES {static}
-    - value : int
+    - intValue : int
     + getInstruction(value : int) : Instruction {static}
     + getIntValue() : int
     + valueOf(name : String) : Instruction {static}
     + values() : Instruction[] {static}
   }
   class VirtualMachine {
+    - LOGGER : Logger {static}
     - stack : Stack<Integer>
     - wizards : Wizard[]
     + VirtualMachine()
+    + VirtualMachine(wizard1 : Wizard, wizard2 : Wizard)
     + execute(bytecode : int[])
     + getAgility(wizard : int) : int
     + getHealth(wizard : int) : int
     + getStack() : Stack<Integer>
     + getWisdom(wizard : int) : int
     + getWizards() : Wizard[]
+    - randomInt(min : int, max : int) : int
     + setAgility(wizard : int, amount : int)
     + setHealth(wizard : int, amount : int)
     + setWisdom(wizard : int, amount : int)
@@ -45,7 +47,7 @@ package com.iluwatar.bytecode {
     - numberOfPlayedSounds : int
     - numberOfSpawnedParticles : int
     - wisdom : int
-    + Wizard()
+    + Wizard(health : int, agility : int, wisdom : int, numberOfPlayedSounds : int, numberOfSpawnedParticles : int)
     + getAgility() : int
     + getHealth() : int
     + getNumberOfPlayedSounds() : int
@@ -54,6 +56,8 @@ package com.iluwatar.bytecode {
     + playSound()
     + setAgility(agility : int)
     + setHealth(health : int)
+    + setNumberOfPlayedSounds(numberOfPlayedSounds : int)
+    + setNumberOfSpawnedParticles(numberOfSpawnedParticles : int)
     + setWisdom(wisdom : int)
     + spawnParticles()
   }

bytecode/pom.xml

@@ -29,7 +29,7 @@
 	<parent>
 		<artifactId>java-design-patterns</artifactId>
 		<groupId>com.iluwatar</groupId>
-		<version>1.24.0-SNAPSHOT</version>
+		<version>1.25.0-SNAPSHOT</version>
 	</parent>
 	<modelVersion>4.0.0</modelVersion>
 

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

@@ -49,33 +49,21 @@ public class App {
    */
   public static void main(String[] args) {
 
-    var wizard = new Wizard();
-    wizard.setHealth(45);
-    wizard.setAgility(7);
-    wizard.setWisdom(11);
+    var vm = new VirtualMachine(
+        new Wizard(45, 7, 11, 0, 0),
+        new Wizard(36, 18, 8, 0, 0));
 
-    var vm = new VirtualMachine();
-    vm.getWizards()[0] = wizard;
-
-    String literal = "LITERAL 0";
-
-    interpretInstruction(literal, vm);
-    interpretInstruction(literal, vm);
-    interpretInstruction("GET_HEALTH", vm);
-    interpretInstruction(literal, vm);
-    interpretInstruction("GET_AGILITY", vm);
-    interpretInstruction(literal, vm);
-    interpretInstruction("GET_WISDOM ", vm);
-    interpretInstruction("ADD", vm);
-    interpretInstruction("LITERAL 2", vm);
-    interpretInstruction("DIVIDE", vm);
-    interpretInstruction("ADD", vm);
-    interpretInstruction("SET_HEALTH", vm);
-  }
-
-  private static void interpretInstruction(String instruction, VirtualMachine vm) {
-    vm.execute(InstructionConverterUtil.convertToByteCode(instruction));
-    var stack = vm.getStack();
-    LOGGER.info(instruction + String.format("%" + (12 - instruction.length()) + "s", "") + stack);
+    vm.execute(InstructionConverterUtil.convertToByteCode("LITERAL 0"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("LITERAL 0"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("GET_HEALTH"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("LITERAL 0"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("GET_AGILITY"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("LITERAL 0"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("GET_WISDOM"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("ADD"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("LITERAL 2"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("DIVIDE"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("ADD"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("SET_HEALTH"));
   }
 }

bytecode/src/main/java/com/iluwatar/bytecode/Instruction.java

@@ -33,17 +33,17 @@ import lombok.Getter;
 @Getter
 public enum Instruction {
 
-  LITERAL(1),
-  SET_HEALTH(2),
-  SET_WISDOM(3),
-  SET_AGILITY(4),
-  PLAY_SOUND(5),
-  SPAWN_PARTICLES(6),
-  GET_HEALTH(7),
-  GET_AGILITY(8),
-  GET_WISDOM(9),
-  ADD(10),
-  DIVIDE(11);
+  LITERAL(1),         // e.g. "LITERAL 0", push 0 to stack
+  SET_HEALTH(2),      // e.g. "SET_HEALTH", pop health and wizard number, call set health
+  SET_WISDOM(3),      // e.g. "SET_WISDOM", pop wisdom and wizard number, call set wisdom
+  SET_AGILITY(4),     // e.g. "SET_AGILITY", pop agility and wizard number, call set agility
+  PLAY_SOUND(5),      // e.g. "PLAY_SOUND", pop value as wizard number, call play sound
+  SPAWN_PARTICLES(6), // e.g. "SPAWN_PARTICLES", pop value as wizard number, call spawn particles
+  GET_HEALTH(7),      // e.g. "GET_HEALTH", pop value as wizard number, push wizard's health
+  GET_AGILITY(8),     // e.g. "GET_AGILITY", pop value as wizard number, push wizard's agility
+  GET_WISDOM(9),      // e.g. "GET_WISDOM", pop value as wizard number, push wizard's wisdom
+  ADD(10),            // e.g. "ADD", pop 2 values, push their sum
+  DIVIDE(11);         // e.g. "DIVIDE", pop 2 values, push their division
 
   private final int intValue;
 

bytecode/src/main/java/com/iluwatar/bytecode/VirtualMachine.java

@@ -24,12 +24,15 @@
 package com.iluwatar.bytecode;
 
 import java.util.Stack;
+import java.util.concurrent.ThreadLocalRandom;
 import lombok.Getter;
+import lombok.extern.slf4j.Slf4j;
 
 /**
  * Implementation of virtual machine.
  */
 @Getter
+@Slf4j
 public class VirtualMachine {
 
   private final Stack<Integer> stack = new Stack<>();
@@ -37,12 +40,21 @@ public class VirtualMachine {
   private final Wizard[] wizards = new Wizard[2];
 
   /**
-   * Constructor.
+   * No-args constructor.
    */
   public VirtualMachine() {
-    for (var i = 0; i < wizards.length; i++) {
-      wizards[i] = new Wizard();
-    }
+    wizards[0] = new Wizard(randomInt(3, 32), randomInt(3, 32), randomInt(3, 32),
+        0, 0);
+    wizards[1] = new Wizard(randomInt(3, 32), randomInt(3, 32), randomInt(3, 32),
+        0, 0);
+  }
+
+  /**
+   * Constructor taking the wizards as arguments.
+   */
+  public VirtualMachine(Wizard wizard1, Wizard wizard2) {
+    wizards[0] = wizard1;
+    wizards[1] = wizard2;
   }
 
   /**
@@ -57,6 +69,7 @@ public class VirtualMachine {
         case LITERAL:
           // Read the next byte from the bytecode.
           int value = bytecode[++i];
+          // Push the next value to stack
           stack.push(value);
           break;
         case SET_AGILITY:
@@ -107,6 +120,7 @@ public class VirtualMachine {
         default:
           throw new IllegalArgumentException("Invalid instruction value");
       }
+      LOGGER.info("Executed " + instruction.name() + ", Stack contains " + getStack());
     }
   }
 
@@ -133,4 +147,8 @@ public class VirtualMachine {
   public int getAgility(int wizard) {
     return wizards[wizard].getAgility();
   }
+
+  private int randomInt(int min, int max) {
+    return ThreadLocalRandom.current().nextInt(min, max + 1);
+  }
 }

bytecode/src/main/java/com/iluwatar/bytecode/Wizard.java

@@ -23,6 +23,7 @@
 
 package com.iluwatar.bytecode;
 
+import lombok.AllArgsConstructor;
 import lombok.Getter;
 import lombok.Setter;
 import lombok.extern.slf4j.Slf4j;
@@ -31,16 +32,15 @@ import lombok.extern.slf4j.Slf4j;
  * This class represent game objects which properties can be changed by instructions interpreted by
  * virtual machine.
  */
+@AllArgsConstructor
 @Setter
 @Getter
 @Slf4j
 public class Wizard {
 
   private int health;
-
   private int agility;
   private int wisdom;
-
   private int numberOfPlayedSounds;
   private int numberOfSpawnedParticles;
 
@@ -53,5 +53,4 @@ public class Wizard {
     LOGGER.info("Spawning particles");
     numberOfSpawnedParticles++;
   }
-
 }

bytecode/src/main/java/com/iluwatar/bytecode/util/InstructionConverterUtil.java

@@ -73,6 +73,4 @@ public class InstructionConverterUtil {
       return false;
     }
   }
-
-
 }

caching/README.md

@@ -4,26 +4,342 @@ title: Caching
 folder: caching
 permalink: /patterns/caching/
 categories: Behavioral
+language: en
 tags:
   - Performance
   - Cloud distributed
 ---
 
 ## Intent
-To avoid expensive re-acquisition of resources by not releasing
-the resources immediately after their use. The resources retain their identity, are kept in some
-fast-access storage, and are re-used to avoid having to acquire them again.
+
+The caching pattern avoids expensive re-acquisition of resources by not releasing them immediately 
+after use. The resources retain their identity, are kept in some fast-access storage, and are 
+re-used to avoid having to acquire them again.
+
+## Explanation
+
+Real world example
+
+> A team is working on a website that provides new homes for abandoned cats. People can post their
+> cats on the website after registering, but all the new posts require approval from one of the
+> site moderators. The user accounts of the site moderators contain a specific flag and the data
+> is stored in a MongoDB database. Checking for the moderator flag each time a post is viewed 
+> becomes expensive and it's a good idea to utilize caching here.
+
+In plain words
+
+> Caching pattern keeps frequently needed data in fast-access storage to improve performance.
+
+Wikipedia says:
+
+> In computing, a cache is a hardware or software component that stores data so that future 
+> requests for that data can be served faster; the data stored in a cache might be the result of 
+> an earlier computation or a copy of data stored elsewhere. A cache hit occurs when the requested 
+> data can be found in a cache, while a cache miss occurs when it cannot. Cache hits are served by 
+> reading data from the cache, which is faster than recomputing a result or reading from a slower 
+> data store; thus, the more requests that can be served from the cache, the faster the system 
+> performs.
+
+**Programmatic Example**
+
+Let's first look at the data layer of our application. The interesting classes are `UserAccount`
+which is a simple Java object containing the user account details, and `DbManager` interface which handles
+reading and writing of these objects to/from database.
+
+```java
+@Data
+@AllArgsConstructor
+@ToString
+@EqualsAndHashCode
+public class UserAccount {
+  private String userId;
+  private String userName;
+  private String additionalInfo;
+}
+
+public interface DbManager {
+
+  void connect();
+  void disconnect();
+  
+  UserAccount readFromDb(String userId);
+  UserAccount writeToDb(UserAccount userAccount);
+  UserAccount updateDb(UserAccount userAccount);
+  UserAccount upsertDb(UserAccount userAccount);
+}
+```
+
+In the example, we are demonstrating various different caching policies
+
+* Write-through writes data to the cache and DB in a single transaction
+* Write-around writes data immediately into the DB instead of the cache
+* Write-behind writes data into the cache initially whilst the data is only written into the DB 
+  when the cache is full
+* Cache-aside pushes the responsibility of keeping the data synchronized in both data sources to 
+  the application itself
+* Read-through strategy is also included in the aforementioned strategies and it returns data from 
+  the cache to the caller if it exists, otherwise queries from DB and stores it into the cache for 
+  future use.
+  
+The cache implementation in `LruCache` is a hash table accompanied by a doubly 
+linked-list. The linked-list helps in capturing and maintaining the LRU data in the cache. When 
+data is queried (from the cache), added (to the cache), or updated, the data is moved to the front 
+of the list to depict itself as the most-recently-used data. The LRU data is always at the end of 
+the list.
+
+```java
+@Slf4j
+public class LruCache {
+
+  static class Node {
+    String userId;
+    UserAccount userAccount;
+    Node previous;
+    Node next;
+
+    public Node(String userId, UserAccount userAccount) {
+      this.userId = userId;
+      this.userAccount = userAccount;
+    }
+  }
+  
+  /* ... omitted details ... */
+
+  public LruCache(int capacity) {
+    this.capacity = capacity;
+  }
+
+  public UserAccount get(String userId) {
+    if (cache.containsKey(userId)) {
+      var node = cache.get(userId);
+      remove(node);
+      setHead(node);
+      return node.userAccount;
+    }
+    return null;
+  }
+
+  public void set(String userId, UserAccount userAccount) {
+    if (cache.containsKey(userId)) {
+      var old = cache.get(userId);
+      old.userAccount = userAccount;
+      remove(old);
+      setHead(old);
+    } else {
+      var newNode = new Node(userId, userAccount);
+      if (cache.size() >= capacity) {
+        LOGGER.info("# Cache is FULL! Removing {} from cache...", end.userId);
+        cache.remove(end.userId); // remove LRU data from cache.
+        remove(end);
+        setHead(newNode);
+      } else {
+        setHead(newNode);
+      }
+      cache.put(userId, newNode);
+    }
+  }
+
+  public boolean contains(String userId) {
+    return cache.containsKey(userId);
+  }
+  
+  public void remove(Node node) { /* ... */ }
+  public void setHead(Node node) { /* ... */ }
+  public void invalidate(String userId) { /* ... */ }
+  public boolean isFull() { /* ... */ }
+  public UserAccount getLruData() { /* ... */ }
+  public void clear() { /* ... */ }
+  public List<UserAccount> getCacheDataInListForm() { /* ... */ }
+  public void setCapacity(int newCapacity) { /* ... */ }
+}
+```
+
+The next layer we are going to look at is `CacheStore` which implements the different caching
+strategies.
+
+```java
+@Slf4j
+public class CacheStore {
+
+  private static final int CAPACITY = 3;
+  private static LruCache cache;
+  private final DbManager dbManager;
+
+  /* ... details omitted ... */
+
+  public UserAccount readThrough(final String userId) {
+    if (cache.contains(userId)) {
+      LOGGER.info("# Found in Cache!");
+      return cache.get(userId);
+    }
+    LOGGER.info("# Not found in cache! Go to DB!!");
+    UserAccount userAccount = dbManager.readFromDb(userId);
+    cache.set(userId, userAccount);
+    return userAccount;
+  }
+
+  public void writeThrough(final UserAccount userAccount) {
+    if (cache.contains(userAccount.getUserId())) {
+      dbManager.updateDb(userAccount);
+    } else {
+      dbManager.writeToDb(userAccount);
+    }
+    cache.set(userAccount.getUserId(), userAccount);
+  }
+
+  public void writeAround(final UserAccount userAccount) {
+    if (cache.contains(userAccount.getUserId())) {
+      dbManager.updateDb(userAccount);
+      // Cache data has been updated -- remove older
+      cache.invalidate(userAccount.getUserId());
+      // version from cache.
+    } else {
+      dbManager.writeToDb(userAccount);
+    }
+  }
+
+  public static void clearCache() {
+    if (cache != null) {
+      cache.clear();
+    }
+  }
+
+  public static void flushCache() {
+    LOGGER.info("# flushCache...");
+    Optional.ofNullable(cache)
+        .map(LruCache::getCacheDataInListForm)
+        .orElse(List.of())
+        .forEach(DbManager::updateDb);
+  }
+
+  /* ... omitted the implementation of other caching strategies ... */
+
+}
+```
+
+`AppManager` helps to bridge the gap in communication between the main class and the application's
+back-end. DB connection is initialized through this class. The chosen caching strategy/policy is
+also initialized here. Before the cache can be used, the size of the cache has to be set. Depending 
+on the chosen caching policy, `AppManager` will call the appropriate function in the `CacheStore` 
+class.
+
+```java
+@Slf4j
+public final class AppManager {
+
+  private static CachingPolicy cachingPolicy;
+  private final DbManager dbManager;
+  private final CacheStore cacheStore;
+
+  private AppManager() {
+  }
+
+  public void initDb() { /* ... */ }
+
+  public static void initCachingPolicy(CachingPolicy policy) { /* ... */ }
+
+  public static void initCacheCapacity(int capacity) { /* ... */ }
+
+  public UserAccount find(final String userId) {
+    LOGGER.info("Trying to find {} in cache", userId);
+    if (cachingPolicy == CachingPolicy.THROUGH
+            || cachingPolicy == CachingPolicy.AROUND) {
+      return cacheStore.readThrough(userId);
+    } else if (cachingPolicy == CachingPolicy.BEHIND) {
+      return cacheStore.readThroughWithWriteBackPolicy(userId);
+    } else if (cachingPolicy == CachingPolicy.ASIDE) {
+      return findAside(userId);
+    }
+    return null;
+  }
+
+  public void save(final UserAccount userAccount) {
+    LOGGER.info("Save record!");
+    if (cachingPolicy == CachingPolicy.THROUGH) {
+      cacheStore.writeThrough(userAccount);
+    } else if (cachingPolicy == CachingPolicy.AROUND) {
+      cacheStore.writeAround(userAccount);
+    } else if (cachingPolicy == CachingPolicy.BEHIND) {
+      cacheStore.writeBehind(userAccount);
+    } else if (cachingPolicy == CachingPolicy.ASIDE) {
+      saveAside(userAccount);
+    }
+  }
+
+  public static String printCacheContent() {
+    return CacheStore.print();
+  }
+
+  /* ... details omitted ... */
+}
+```
+
+Here is what we do in the main class of the application.
+
+```java
+@Slf4j
+public class App {
+
+  public static void main(final String[] args) {
+    boolean isDbMongo = isDbMongo(args);
+    if(isDbMongo){
+      LOGGER.info("Using the Mongo database engine to run the application.");
+    } else {
+      LOGGER.info("Using the 'in Memory' database to run the application.");
+    }
+    App app = new App(isDbMongo);
+    app.useReadAndWriteThroughStrategy();
+    String splitLine = "==============================================";
+    LOGGER.info(splitLine);
+    app.useReadThroughAndWriteAroundStrategy();
+    LOGGER.info(splitLine);
+    app.useReadThroughAndWriteBehindStrategy();
+    LOGGER.info(splitLine);
+    app.useCacheAsideStategy();
+    LOGGER.info(splitLine);
+  }
+
+  public void useReadAndWriteThroughStrategy() {
+    LOGGER.info("# CachingPolicy.THROUGH");
+    appManager.initCachingPolicy(CachingPolicy.THROUGH);
+
+    var userAccount1 = new UserAccount("001", "John", "He is a boy.");
+
+    appManager.save(userAccount1);
+    LOGGER.info(appManager.printCacheContent());
+    appManager.find("001");
+    appManager.find("001");
+  }
+
+  public void useReadThroughAndWriteAroundStrategy() { /* ... */ }
+
+  public void useReadThroughAndWriteBehindStrategy() { /* ... */ }
+
+  public void useCacheAsideStategy() { /* ... */ }
+}
+```
 
 ## Class diagram
+
 ![alt text](./etc/caching.png "Caching")
 
 ## Applicability
+
 Use the Caching pattern(s) when
 
-* Repetitious acquisition, initialization, and release of the same resource causes unnecessary performance overhead.
+* Repetitious acquisition, initialization, and release of the same resource cause unnecessary 
+  performance overhead.
+
+## Related patterns
+
+* [Proxy](https://java-design-patterns.com/patterns/proxy/)
 
 ## Credits
 
 * [Write-through, write-around, write-back: Cache explained](http://www.computerweekly.com/feature/Write-through-write-around-write-back-Cache-explained)
 * [Read-Through, Write-Through, Write-Behind, and Refresh-Ahead Caching](https://docs.oracle.com/cd/E15357_01/coh.360/e15723/cache_rtwtwbra.htm#COHDG5177)
 * [Cache-Aside pattern](https://docs.microsoft.com/en-us/azure/architecture/patterns/cache-aside)
+* [Java EE 8 High Performance: Master techniques such as memory optimization, caching, concurrency, and multithreading to achieve maximum performance from your enterprise applications](https://www.amazon.com/gp/product/178847306X/ref=as_li_qf_asin_il_tl?ie=UTF8&tag=javadesignpat-20&creative=9325&linkCode=as2&creativeASIN=178847306X&linkId=e948720055599f248cdac47da9125ff4)
+* [Java Performance: In-Depth Advice for Tuning and Programming Java 8, 11, and Beyond](https://www.amazon.com/gp/product/1492056111/ref=as_li_qf_asin_il_tl?ie=UTF8&tag=javadesignpat-20&creative=9325&linkCode=as2&creativeASIN=1492056111&linkId=7e553581559b9ec04221259e52004b08)
+* [Effective Java](https://www.amazon.com/gp/product/B078H61SCH/ref=as_li_qf_asin_il_tl?ie=UTF8&tag=javadesignpat-20&creative=9325&linkCode=as2&creativeASIN=B078H61SCH&linkId=f06607a0b48c76541ef19c5b8b9e7882)
+* [Java Performance: The Definitive Guide: Getting the Most Out of Your Code](https://www.amazon.com/gp/product/1449358454/ref=as_li_qf_asin_il_tl?ie=UTF8&tag=javadesignpat-20&creative=9325&linkCode=as2&creativeASIN=1449358454&linkId=475c18363e350630cc0b39ab681b2687)

caching/docker-compose.yml

@@ -0,0 +1,11 @@
+version: '3.7'
+services:
+  mongodb_container:
+    image: mongo:latest
+    environment:
+      MONGO_INITDB_ROOT_USERNAME: root
+      MONGO_INITDB_ROOT_PASSWORD: rootpassword
+    ports:
+      - 27017:27017
+    volumes:
+      - ./mongo-data/:/data/db

caching/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.24.0-SNAPSHOT</version>
+    <version>1.25.0-SNAPSHOT</version>
   </parent>
   <artifactId>caching</artifactId>
   <dependencies>
@@ -39,19 +39,21 @@
       <scope>test</scope>
     </dependency>
     <dependency>
-      <groupId>org.mongodb</groupId>
-      <artifactId>mongodb-driver</artifactId>
-      <version>3.12.1</version>
+      <groupId>org.mockito</groupId>
+      <artifactId>mockito-junit-jupiter</artifactId>
+      <version>3.12.4</version>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.mockito</groupId>
+      <artifactId>mockito-all</artifactId>
+      <version>1.10.19</version>
+      <scope>test</scope>
     </dependency>
     <dependency>
       <groupId>org.mongodb</groupId>
-      <artifactId>mongodb-driver-core</artifactId>
-      <version>3.0.4</version>
-    </dependency>
-    <dependency>
-      <groupId>org.mongodb</groupId>
-      <artifactId>bson</artifactId>
-      <version>3.0.4</version>
+      <artifactId>mongo-java-driver</artifactId>
+      <version>3.4.1</version>
     </dependency>
   </dependencies>
   <!--

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

@@ -1,58 +1,62 @@
-/*
- * 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.caching;
 
+import com.iluwatar.caching.database.DbManager;
+import com.iluwatar.caching.database.DbManagerFactory;
 import lombok.extern.slf4j.Slf4j;
 
 /**
- * The Caching pattern describes how to avoid expensive re-acquisition of resources by not releasing
- * the resources immediately after their use. The resources retain their identity, are kept in some
- * fast-access storage, and are re-used to avoid having to acquire them again. There are four main
- * caching strategies/techniques in this pattern; each with their own pros and cons. They are;
- * <code>write-through</code> which writes data to the cache and DB in a single transaction,
- * <code>write-around</code> which writes data immediately into the DB instead of the cache,
- * <code>write-behind</code> which writes data into the cache initially whilst the data is only
- * written into the DB when the cache is full, and <code>cache-aside</code> which pushes the
- * responsibility of keeping the data synchronized in both data sources to the application itself.
- * The <code>read-through</code> strategy is also included in the mentioned four strategies --
- * returns data from the cache to the caller <b>if</b> it exists <b>else</b> queries from DB and
- * stores it into the cache for future use. These strategies determine when the data in the cache
- * should be written back to the backing store (i.e. Database) and help keep both data sources
- * synchronized/up-to-date. This pattern can improve performance and also helps to maintain
- * consistency between data held in the cache and the data in the underlying data store.
+ * The Caching pattern describes how to avoid expensive re-acquisition of
+ * resources by not releasing the resources immediately after their use.
+ * The resources retain their identity, are kept in some fast-access storage,
+ * and are re-used to avoid having to acquire them again. There are four main
+ * caching strategies/techniques in this pattern; each with their own pros and
+ * cons. They are <code>write-through</code> which writes data to the cache and
+ * DB in a single transaction, <code>write-around</code> which writes data
+ * immediately into the DB instead of the cache, <code>write-behind</code>
+ * which writes data into the cache initially whilst the data is only
+ * written into the DB when the cache is full, and <code>cache-aside</code>
+ * which pushes the responsibility of keeping the data synchronized in both
+ * data sources to the application itself. The <code>read-through</code>
+ * strategy is also included in the mentioned four strategies --
+ * returns data from the cache to the caller <b>if</b> it exists <b>else</b>
+ * queries from DB and stores it into the cache for future use. These strategies
+ * determine when the data in the cache should be written back to the backing
+ * store (i.e. Database) and help keep both data sources
+ * synchronized/up-to-date. This pattern can improve performance and also helps
+ * to maintainconsistency between data held in the cache and the data in
+ * the underlying data store.
  *
- * <p>In this example, the user account ({@link UserAccount}) entity is used as the underlying
- * application data. The cache itself is implemented as an internal (Java) data structure. It adopts
- * a Least-Recently-Used (LRU) strategy for evicting data from itself when its full. The four
- * strategies are individually tested. The testing of the cache is restricted towards saving and
- * querying of user accounts from the underlying data store ( {@link DbManager}). The main class (
- * {@link App} is not aware of the underlying mechanics of the application (i.e. save and query) and
- * whether the data is coming from the cache or the DB (i.e. separation of concern). The AppManager
- * ({@link AppManager}) handles the transaction of data to-and-from the underlying data store
- * (depending on the preferred caching policy/strategy).
+ * <p>In this example, the user account ({@link UserAccount}) entity is used
+ * as the underlying application data. The cache itself is implemented as an
+ * internal (Java) data structure. It adopts a Least-Recently-Used (LRU)
+ * strategy for evicting data from itself when its full. The four
+ * strategies are individually tested. The testing of the cache is restricted
+ * towards saving and querying of user accounts from the
+ * underlying data store( {@link DbManager}). The main class ( {@link App}
+ * is not aware of the underlying mechanics of the application
+ * (i.e. save and query) and whether the data is coming from the cache or the
+ * DB (i.e. separation of concern). The AppManager ({@link AppManager}) handles
+ * the transaction of data to-and-from the underlying data store (depending on
+ * the preferred caching policy/strategy).
  * <p>
- * <i>{@literal App --> AppManager --> CacheStore/LRUCache/CachingPolicy --> DBManager} </i>
+ * <i>{@literal App --> AppManager --> CacheStore/LRUCache/CachingPolicy -->
+ * DBManager} </i>
+ * </p>
+ *
+ * <p>
+ * There are 2 ways to launch the application.
+ *  - to use "in Memory" database.
+ *  - to use the MongoDb as a database
+ *
+ * To run the application with "in Memory" database, just launch it without parameters
+ * Example: 'java -jar app.jar'
+ *
+ * To run the application with MongoDb you need to be installed the MongoDb
+ * in your system, or to launch it in the docker container.
+ * You may launch docker container from the root of current module with command:
+ * 'docker-compose up'
+ * Then you can start the application with parameter --mongo
+ * Example: 'java -jar app.jar --mongo'
  * </p>
  *
  * @see CacheStore
@@ -61,23 +65,67 @@ import lombok.extern.slf4j.Slf4j;
  */
 @Slf4j
 public class App {
+  /**
+   * Constant parameter name to use mongoDB.
+   */
+  private static final String USE_MONGO_DB = "--mongo";
+  /**
+   * Application manager.
+   */
+  private final AppManager appManager;
+
+  /**
+   * Constructor of current App.
+   *
+   * @param isMongo boolean
+   */
+  public App(final boolean isMongo) {
+    DbManager dbManager = DbManagerFactory.initDb(isMongo);
+    appManager = new AppManager(dbManager);
+    appManager.initDb();
+  }
 
   /**
    * Program entry point.
    *
    * @param args command line args
    */
-  public static void main(String[] args) {
-    AppManager.initDb(false); // VirtualDB (instead of MongoDB) was used in running the JUnit tests
+  public static void main(final String[] args) {
+    // VirtualDB (instead of MongoDB) was used in running the JUnit tests
     // and the App class to avoid Maven compilation errors. Set flag to
     // true to run the tests with MongoDB (provided that MongoDB is
     // installed and socket connection is open).
-    AppManager.initCacheCapacity(3);
-    var app = new App();
+    boolean isDbMongo = isDbMongo(args);
+    if (isDbMongo) {
+      LOGGER.info("Using the Mongo database engine to run the application.");
+    } else {
+      LOGGER.info("Using the 'in Memory' database to run the application.");
+    }
+    App app = new App(isDbMongo);
     app.useReadAndWriteThroughStrategy();
+    String splitLine = "==============================================";
+    LOGGER.info(splitLine);
     app.useReadThroughAndWriteAroundStrategy();
+    LOGGER.info(splitLine);
     app.useReadThroughAndWriteBehindStrategy();
+    LOGGER.info(splitLine);
     app.useCacheAsideStategy();
+    LOGGER.info(splitLine);
+  }
+
+  /**
+   * Check the input parameters. if
+   *
+   * @param args input params
+   * @return true if there is "--mongo" parameter in arguments
+   */
+  private static boolean isDbMongo(final String[] args) {
+    for (String arg : args) {
+      if (arg.equals(USE_MONGO_DB)) {
+        return true;
+      }
+    }
+    return false;
   }
 
   /**
@@ -85,14 +133,14 @@ public class App {
    */
   public void useReadAndWriteThroughStrategy() {
     LOGGER.info("# CachingPolicy.THROUGH");
-    AppManager.initCachingPolicy(CachingPolicy.THROUGH);
+    appManager.initCachingPolicy(CachingPolicy.THROUGH);
 
     var userAccount1 = new UserAccount("001", "John", "He is a boy.");
 
-    AppManager.save(userAccount1);
-    LOGGER.info(AppManager.printCacheContent());
-    AppManager.find("001");
-    AppManager.find("001");
+    appManager.save(userAccount1);
+    LOGGER.info(appManager.printCacheContent());
+    appManager.find("001");
+    appManager.find("001");
   }
 
   /**
@@ -100,21 +148,21 @@ public class App {
    */
   public void useReadThroughAndWriteAroundStrategy() {
     LOGGER.info("# CachingPolicy.AROUND");
-    AppManager.initCachingPolicy(CachingPolicy.AROUND);
+    appManager.initCachingPolicy(CachingPolicy.AROUND);
 
     var userAccount2 = new UserAccount("002", "Jane", "She is a girl.");
 
-    AppManager.save(userAccount2);
-    LOGGER.info(AppManager.printCacheContent());
-    AppManager.find("002");
-    LOGGER.info(AppManager.printCacheContent());
-    userAccount2 = AppManager.find("002");
+    appManager.save(userAccount2);
+    LOGGER.info(appManager.printCacheContent());
+    appManager.find("002");
+    LOGGER.info(appManager.printCacheContent());
+    userAccount2 = appManager.find("002");
     userAccount2.setUserName("Jane G.");
-    AppManager.save(userAccount2);
-    LOGGER.info(AppManager.printCacheContent());
-    AppManager.find("002");
-    LOGGER.info(AppManager.printCacheContent());
-    AppManager.find("002");
+    appManager.save(userAccount2);
+    LOGGER.info(appManager.printCacheContent());
+    appManager.find("002");
+    LOGGER.info(appManager.printCacheContent());
+    appManager.find("002");
   }
 
   /**
@@ -122,23 +170,31 @@ public class App {
    */
   public void useReadThroughAndWriteBehindStrategy() {
     LOGGER.info("# CachingPolicy.BEHIND");
-    AppManager.initCachingPolicy(CachingPolicy.BEHIND);
+    appManager.initCachingPolicy(CachingPolicy.BEHIND);
 
-    var userAccount3 = new UserAccount("003", "Adam", "He likes food.");
-    var userAccount4 = new UserAccount("004", "Rita", "She hates cats.");
-    var userAccount5 = new UserAccount("005", "Isaac", "He is allergic to mustard.");
+    var userAccount3 = new UserAccount("003",
+            "Adam",
+            "He likes food.");
+    var userAccount4 = new UserAccount("004",
+            "Rita",
+            "She hates cats.");
+    var userAccount5 = new UserAccount("005",
+            "Isaac",
+            "He is allergic to mustard.");
 
-    AppManager.save(userAccount3);
-    AppManager.save(userAccount4);
-    AppManager.save(userAccount5);
-    LOGGER.info(AppManager.printCacheContent());
-    AppManager.find("003");
-    LOGGER.info(AppManager.printCacheContent());
-    UserAccount userAccount6 = new UserAccount("006", "Yasha", "She is an only child.");
-    AppManager.save(userAccount6);
-    LOGGER.info(AppManager.printCacheContent());
-    AppManager.find("004");
-    LOGGER.info(AppManager.printCacheContent());
+    appManager.save(userAccount3);
+    appManager.save(userAccount4);
+    appManager.save(userAccount5);
+    LOGGER.info(appManager.printCacheContent());
+    appManager.find("003");
+    LOGGER.info(appManager.printCacheContent());
+    UserAccount userAccount6 = new UserAccount("006",
+            "Yasha",
+            "She is an only child.");
+    appManager.save(userAccount6);
+    LOGGER.info(appManager.printCacheContent());
+    appManager.find("004");
+    LOGGER.info(appManager.printCacheContent());
   }
 
   /**
@@ -146,20 +202,26 @@ public class App {
    */
   public void useCacheAsideStategy() {
     LOGGER.info("# CachingPolicy.ASIDE");
-    AppManager.initCachingPolicy(CachingPolicy.ASIDE);
-    LOGGER.info(AppManager.printCacheContent());
+    appManager.initCachingPolicy(CachingPolicy.ASIDE);
+    LOGGER.info(appManager.printCacheContent());
 
-    var userAccount3 = new UserAccount("003", "Adam", "He likes food.");
-    var userAccount4 = new UserAccount("004", "Rita", "She hates cats.");
-    var userAccount5 = new UserAccount("005", "Isaac", "He is allergic to mustard.");
-    AppManager.save(userAccount3);
-    AppManager.save(userAccount4);
-    AppManager.save(userAccount5);
+    var userAccount3 = new UserAccount("003",
+            "Adam",
+            "He likes food.");
+    var userAccount4 = new UserAccount("004",
+            "Rita",
+            "She hates cats.");
+    var userAccount5 = new UserAccount("005",
+            "Isaac",
+            "He is allergic to mustard.");
+    appManager.save(userAccount3);
+    appManager.save(userAccount4);
+    appManager.save(userAccount5);
 
-    LOGGER.info(AppManager.printCacheContent());
-    AppManager.find("003");
-    LOGGER.info(AppManager.printCacheContent());
-    AppManager.find("004");
-    LOGGER.info(AppManager.printCacheContent());
+    LOGGER.info(appManager.printCacheContent());
+    appManager.find("003");
+    LOGGER.info(appManager.printCacheContent());
+    appManager.find("004");
+    LOGGER.info(appManager.printCacheContent());
   }
 }

caching/src/main/java/com/iluwatar/caching/AppManager.java

@@ -23,63 +23,80 @@
 
 package com.iluwatar.caching;
 
-import java.text.ParseException;
+import com.iluwatar.caching.database.DbManager;
+
 import java.util.Optional;
 
+import lombok.extern.slf4j.Slf4j;
+
 /**
- * AppManager helps to bridge the gap in communication between the main class and the application's
- * back-end. DB connection is initialized through this class. The chosen caching strategy/policy is
- * also initialized here. Before the cache can be used, the size of the cache has to be set.
- * Depending on the chosen caching policy, AppManager will call the appropriate function in the
- * CacheStore class.
+ * AppManager helps to bridge the gap in communication between the main class
+ * and the application's back-end. DB connection is initialized through this
+ * class. The chosen  caching strategy/policy is also initialized here.
+ * Before the cache can be used, the size of the  cache has to be set.
+ * Depending on the chosen caching policy, AppManager will call the
+ * appropriate function in the CacheStore class.
  */
-public final class AppManager {
+@Slf4j
+public class AppManager {
+  /**
+   * Caching Policy.
+   */
+  private CachingPolicy cachingPolicy;
+  /**
+   * Database Manager.
+   */
+  private final DbManager dbManager;
+  /**
+   * Cache Store.
+   */
+  private final CacheStore cacheStore;
 
-  private static CachingPolicy cachingPolicy;
-
-  private AppManager() {
+  /**
+   * Constructor.
+   *
+   * @param newDbManager database manager
+   */
+  public AppManager(final DbManager newDbManager) {
+    this.dbManager = newDbManager;
+    this.cacheStore = new CacheStore(newDbManager);
   }
 
   /**
-   * Developer/Tester is able to choose whether the application should use MongoDB as its underlying
-   * data storage or a simple Java data structure to (temporarily) store the data/objects during
-   * runtime.
+   * Developer/Tester is able to choose whether the application should use
+   * MongoDB as its underlying data storage or a simple Java data structure
+   * to (temporarily) store the data/objects during runtime.
    */
-  public static void initDb(boolean useMongoDb) {
-    if (useMongoDb) {
-      try {
-        DbManager.connect();
-      } catch (ParseException e) {
-        e.printStackTrace();
-      }
-    } else {
-      DbManager.createVirtualDb();
-    }
+  public void initDb() {
+    dbManager.connect();
   }
 
   /**
    * Initialize caching policy.
+   *
+   * @param policy is a {@link CachingPolicy}
    */
-  public static void initCachingPolicy(CachingPolicy policy) {
+  public void initCachingPolicy(final CachingPolicy policy) {
     cachingPolicy = policy;
     if (cachingPolicy == CachingPolicy.BEHIND) {
-      Runtime.getRuntime().addShutdownHook(new Thread(CacheStore::flushCache));
+      Runtime.getRuntime().addShutdownHook(new Thread(cacheStore::flushCache));
     }
-    CacheStore.clearCache();
-  }
-
-  public static void initCacheCapacity(int capacity) {
-    CacheStore.initCapacity(capacity);
+    cacheStore.clearCache();
   }
 
   /**
    * Find user account.
+   *
+   * @param userId String
+   * @return {@link UserAccount}
    */
-  public static UserAccount find(String userId) {
-    if (cachingPolicy == CachingPolicy.THROUGH || cachingPolicy == CachingPolicy.AROUND) {
-      return CacheStore.readThrough(userId);
+  public UserAccount find(final String userId) {
+    LOGGER.info("Trying to find {} in cache", userId);
+    if (cachingPolicy == CachingPolicy.THROUGH
+            || cachingPolicy == CachingPolicy.AROUND) {
+      return cacheStore.readThrough(userId);
     } else if (cachingPolicy == CachingPolicy.BEHIND) {
-      return CacheStore.readThroughWithWriteBackPolicy(userId);
+      return cacheStore.readThroughWithWriteBackPolicy(userId);
     } else if (cachingPolicy == CachingPolicy.ASIDE) {
       return findAside(userId);
     }
@@ -88,41 +105,55 @@ public final class AppManager {
 
   /**
    * Save user account.
+   *
+   * @param userAccount {@link UserAccount}
    */
-  public static void save(UserAccount userAccount) {
+  public void save(final UserAccount userAccount) {
+    LOGGER.info("Save record!");
     if (cachingPolicy == CachingPolicy.THROUGH) {
-      CacheStore.writeThrough(userAccount);
+      cacheStore.writeThrough(userAccount);
     } else if (cachingPolicy == CachingPolicy.AROUND) {
-      CacheStore.writeAround(userAccount);
+      cacheStore.writeAround(userAccount);
     } else if (cachingPolicy == CachingPolicy.BEHIND) {
-      CacheStore.writeBehind(userAccount);
+      cacheStore.writeBehind(userAccount);
     } else if (cachingPolicy == CachingPolicy.ASIDE) {
       saveAside(userAccount);
     }
   }
 
-  public static String printCacheContent() {
-    return CacheStore.print();
+  /**
+   * Returns String.
+   *
+   * @return String
+   */
+  public String printCacheContent() {
+    return cacheStore.print();
   }
 
   /**
    * Cache-Aside save user account helper.
+   *
+   * @param userAccount {@link UserAccount}
    */
-  private static void saveAside(UserAccount userAccount) {
-    DbManager.updateDb(userAccount);
-    CacheStore.invalidate(userAccount.getUserId());
+  private void saveAside(final UserAccount userAccount) {
+    dbManager.updateDb(userAccount);
+    cacheStore.invalidate(userAccount.getUserId());
   }
 
   /**
    * Cache-Aside find user account helper.
+   *
+   * @param userId String
+   * @return {@link UserAccount}
    */
-  private static UserAccount findAside(String userId) {
-    return Optional.ofNullable(CacheStore.get(userId))
-        .or(() -> {
-          Optional<UserAccount> userAccount = Optional.ofNullable(DbManager.readFromDb(userId));
-          userAccount.ifPresent(account -> CacheStore.set(userId, account));
-          return userAccount;
-        })
-        .orElse(null);
+  private UserAccount findAside(final String userId) {
+    return Optional.ofNullable(cacheStore.get(userId))
+            .or(() -> {
+              Optional<UserAccount> userAccount =
+                      Optional.ofNullable(dbManager.readFromDb(userId));
+              userAccount.ifPresent(account -> cacheStore.set(userId, account));
+              return userAccount;
+            })
+            .orElse(null);
   }
 }

caching/src/main/java/com/iluwatar/caching/CacheStore.java

@@ -23,9 +23,11 @@
 
 package com.iluwatar.caching;
 
+import com.iluwatar.caching.database.DbManager;
 import java.util.List;
 import java.util.Optional;
 import java.util.stream.Collectors;
+
 import lombok.extern.slf4j.Slf4j;
 
 /**
@@ -33,16 +35,34 @@ import lombok.extern.slf4j.Slf4j;
  */
 @Slf4j
 public class CacheStore {
+  /**
+   * Cache capacity.
+   */
+  private static final int CAPACITY = 3;
 
-  private static LruCache cache;
+  /**
+   * Lru cache see {@link LruCache}.
+   */
+  private LruCache cache;
+  /**
+   * DbManager.
+   */
+  private final DbManager dbManager;
 
-  private CacheStore() {
+  /**
+   * Cache Store.
+   * @param dataBaseManager {@link DbManager}
+   */
+  public CacheStore(final DbManager dataBaseManager) {
+    this.dbManager = dataBaseManager;
+    initCapacity(CAPACITY);
   }
 
   /**
    * Init cache capacity.
+   * @param capacity int
    */
-  public static void initCapacity(int capacity) {
+  public void initCapacity(final int capacity) {
     if (cache == null) {
       cache = new LruCache(capacity);
     } else {
@@ -52,57 +72,64 @@ public class CacheStore {
 
   /**
    * Get user account using read-through cache.
+   * @param userId {@link String}
+   * @return {@link UserAccount}
    */
-  public static UserAccount readThrough(String userId) {
+  public UserAccount readThrough(final String userId) {
     if (cache.contains(userId)) {
-      LOGGER.info("# Cache Hit!");
+      LOGGER.info("# Found in Cache!");
       return cache.get(userId);
     }
-    LOGGER.info("# Cache Miss!");
-    UserAccount userAccount = DbManager.readFromDb(userId);
+    LOGGER.info("# Not found in cache! Go to DB!!");
+    UserAccount userAccount = dbManager.readFromDb(userId);
     cache.set(userId, userAccount);
     return userAccount;
   }
 
   /**
    * Get user account using write-through cache.
+   * @param userAccount {@link UserAccount}
    */
-  public static void writeThrough(UserAccount userAccount) {
+  public void writeThrough(final UserAccount userAccount) {
     if (cache.contains(userAccount.getUserId())) {
-      DbManager.updateDb(userAccount);
+      dbManager.updateDb(userAccount);
     } else {
-      DbManager.writeToDb(userAccount);
+      dbManager.writeToDb(userAccount);
     }
     cache.set(userAccount.getUserId(), userAccount);
   }
 
   /**
    * Get user account using write-around cache.
+   * @param userAccount {@link UserAccount}
    */
-  public static void writeAround(UserAccount userAccount) {
+  public void writeAround(final UserAccount userAccount) {
     if (cache.contains(userAccount.getUserId())) {
-      DbManager.updateDb(userAccount);
-      cache.invalidate(userAccount.getUserId()); // Cache data has been updated -- remove older
+      dbManager.updateDb(userAccount);
+      // Cache data has been updated -- remove older
+      cache.invalidate(userAccount.getUserId());
       // version from cache.
     } else {
-      DbManager.writeToDb(userAccount);
+      dbManager.writeToDb(userAccount);
     }
   }
 
   /**
    * Get user account using read-through cache with write-back policy.
+   * @param userId {@link String}
+   * @return {@link UserAccount}
    */
-  public static UserAccount readThroughWithWriteBackPolicy(String userId) {
+  public UserAccount readThroughWithWriteBackPolicy(final String userId) {
     if (cache.contains(userId)) {
-      LOGGER.info("# Cache Hit!");
+      LOGGER.info("# Found in cache!");
       return cache.get(userId);
     }
-    LOGGER.info("# Cache Miss!");
-    UserAccount userAccount = DbManager.readFromDb(userId);
+    LOGGER.info("# Not found in Cache!");
+    UserAccount userAccount = dbManager.readFromDb(userId);
     if (cache.isFull()) {
       LOGGER.info("# Cache is FULL! Writing LRU data to DB...");
       UserAccount toBeWrittenToDb = cache.getLruData();
-      DbManager.upsertDb(toBeWrittenToDb);
+      dbManager.upsertDb(toBeWrittenToDb);
     }
     cache.set(userId, userAccount);
     return userAccount;
@@ -110,12 +137,13 @@ public class CacheStore {
 
   /**
    * Set user account.
+   * @param userAccount {@link UserAccount}
    */
-  public static void writeBehind(UserAccount userAccount) {
+  public void writeBehind(final UserAccount userAccount) {
     if (cache.isFull() && !cache.contains(userAccount.getUserId())) {
       LOGGER.info("# Cache is FULL! Writing LRU data to DB...");
       UserAccount toBeWrittenToDb = cache.getLruData();
-      DbManager.upsertDb(toBeWrittenToDb);
+      dbManager.upsertDb(toBeWrittenToDb);
     }
     cache.set(userAccount.getUserId(), userAccount);
   }
@@ -123,7 +151,7 @@ public class CacheStore {
   /**
    * Clears cache.
    */
-  public static void clearCache() {
+  public void clearCache() {
     if (cache != null) {
       cache.clear();
     }
@@ -132,44 +160,51 @@ public class CacheStore {
   /**
    * Writes remaining content in the cache into the DB.
    */
-  public static void flushCache() {
+  public void flushCache() {
     LOGGER.info("# flushCache...");
     Optional.ofNullable(cache)
         .map(LruCache::getCacheDataInListForm)
         .orElse(List.of())
-        .forEach(DbManager::updateDb);
+        .forEach(dbManager::updateDb);
+    dbManager.disconnect();
   }
 
   /**
    * Print user accounts.
+   * @return {@link String}
    */
-  public static String print() {
+  public String print() {
     return Optional.ofNullable(cache)
         .map(LruCache::getCacheDataInListForm)
         .orElse(List.of())
         .stream()
         .map(userAccount -> userAccount.toString() + "\n")
-        .collect(Collectors.joining("", "\n--CACHE CONTENT--\n", "----\n"));
+        .collect(Collectors.joining("", "\n--CACHE CONTENT--\n", "----"));
   }
 
   /**
    * Delegate to backing cache store.
+   * @param userId {@link String}
+   * @return {@link UserAccount}
    */
-  public static UserAccount get(String userId) {
+  public UserAccount get(final String userId) {
     return cache.get(userId);
   }
 
   /**
    * Delegate to backing cache store.
+   * @param userId {@link String}
+   * @param userAccount {@link UserAccount}
    */
-  public static void set(String userId, UserAccount userAccount) {
+  public void set(final String userId, final UserAccount userAccount) {
     cache.set(userId, userAccount);
   }
 
   /**
    * Delegate to backing cache store.
+   * @param userId {@link String}
    */
-  public static void invalidate(String userId) {
+  public void invalidate(final String userId) {
     cache.invalidate(userId);
   }
 }

caching/src/main/java/com/iluwatar/caching/CachingPolicy.java

@@ -32,10 +32,25 @@ import lombok.Getter;
 @AllArgsConstructor
 @Getter
 public enum CachingPolicy {
+  /**
+   * Through.
+   */
   THROUGH("through"),
+  /**
+   * AROUND.
+   */
   AROUND("around"),
+  /**
+   * BEHIND.
+   */
   BEHIND("behind"),
+  /**
+   * ASIDE.
+   */
   ASIDE("aside");
 
+  /**
+   * Policy value.
+   */
   private final String policy;
 }

caching/src/main/java/com/iluwatar/caching/DbManager.java

@@ -1,169 +0,0 @@
-/*
- * 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.caching;
-
-import com.iluwatar.caching.constants.CachingConstants;
-import com.mongodb.MongoClient;
-import com.mongodb.client.MongoDatabase;
-import com.mongodb.client.model.UpdateOptions;
-import java.text.ParseException;
-import java.util.HashMap;
-import java.util.Map;
-import org.bson.Document;
-
-/**
- * <p>DBManager handles the communication with the underlying data store i.e. Database. It contains
- * the implemented methods for querying, inserting, and updating data. MongoDB was used as the
- * database for the application.</p>
- *
- * <p>Developer/Tester is able to choose whether the application should use MongoDB as its
- * underlying data storage (connect()) or a simple Java data structure to (temporarily) store the
- * data/objects during runtime (createVirtualDB()).</p>
- */
-public final class DbManager {
-
-  private static MongoClient mongoClient;
-  private static MongoDatabase db;
-  private static boolean useMongoDB;
-
-  private static Map<String, UserAccount> virtualDB;
-
-  private DbManager() {
-  }
-
-  /**
-   * Create DB.
-   */
-  public static void createVirtualDb() {
-    useMongoDB = false;
-    virtualDB = new HashMap<>();
-  }
-
-  /**
-   * Connect to DB.
-   */
-  public static void connect() throws ParseException {
-    useMongoDB = true;
-    mongoClient = new MongoClient();
-    db = mongoClient.getDatabase("test");
-  }
-
-  /**
-   * Read user account from DB.
-   */
-  public static UserAccount readFromDb(String userId) {
-    if (!useMongoDB) {
-      if (virtualDB.containsKey(userId)) {
-        return virtualDB.get(userId);
-      }
-      return null;
-    }
-    if (db == null) {
-      try {
-        connect();
-      } catch (ParseException e) {
-        e.printStackTrace();
-      }
-    }
-    var iterable = db
-        .getCollection(CachingConstants.USER_ACCOUNT)
-        .find(new Document(CachingConstants.USER_ID, userId));
-    if (iterable == null) {
-      return null;
-    }
-    Document doc = iterable.first();
-    String userName = doc.getString(CachingConstants.USER_NAME);
-    String appInfo = doc.getString(CachingConstants.ADD_INFO);
-    return new UserAccount(userId, userName, appInfo);
-  }
-
-  /**
-   * Write user account to DB.
-   */
-  public static void writeToDb(UserAccount userAccount) {
-    if (!useMongoDB) {
-      virtualDB.put(userAccount.getUserId(), userAccount);
-      return;
-    }
-    if (db == null) {
-      try {
-        connect();
-      } catch (ParseException e) {
-        e.printStackTrace();
-      }
-    }
-    db.getCollection(CachingConstants.USER_ACCOUNT).insertOne(
-        new Document(CachingConstants.USER_ID, userAccount.getUserId())
-            .append(CachingConstants.USER_NAME, userAccount.getUserName())
-            .append(CachingConstants.ADD_INFO, userAccount.getAdditionalInfo())
-    );
-  }
-
-  /**
-   * Update DB.
-   */
-  public static void updateDb(UserAccount userAccount) {
-    if (!useMongoDB) {
-      virtualDB.put(userAccount.getUserId(), userAccount);
-      return;
-    }
-    if (db == null) {
-      try {
-        connect();
-      } catch (ParseException e) {
-        e.printStackTrace();
-      }
-    }
-    db.getCollection(CachingConstants.USER_ACCOUNT).updateOne(
-        new Document(CachingConstants.USER_ID, userAccount.getUserId()),
-        new Document("$set", new Document(CachingConstants.USER_NAME, userAccount.getUserName())
-            .append(CachingConstants.ADD_INFO, userAccount.getAdditionalInfo())));
-  }
-
-  /**
-   * Insert data into DB if it does not exist. Else, update it.
-   */
-  public static void upsertDb(UserAccount userAccount) {
-    if (!useMongoDB) {
-      virtualDB.put(userAccount.getUserId(), userAccount);
-      return;
-    }
-    if (db == null) {
-      try {
-        connect();
-      } catch (ParseException e) {
-        e.printStackTrace();
-      }
-    }
-    db.getCollection(CachingConstants.USER_ACCOUNT).updateOne(
-        new Document(CachingConstants.USER_ID, userAccount.getUserId()),
-        new Document("$set",
-            new Document(CachingConstants.USER_ID, userAccount.getUserId())
-                .append(CachingConstants.USER_NAME, userAccount.getUserName())
-                .append(CachingConstants.ADD_INFO, userAccount.getAdditionalInfo())
-        ),
-        new UpdateOptions().upsert(true)
-    );
-  }
-}

caching/src/main/java/com/iluwatar/caching/LruCache.java

@@ -29,41 +29,83 @@ import java.util.List;
 import java.util.Map;
 import lombok.extern.slf4j.Slf4j;
 
+
 /**
- * Data structure/implementation of the application's cache. The data structure consists of a hash
- * table attached with a doubly linked-list. The linked-list helps in capturing and maintaining the
- * LRU data in the cache. When a data is queried (from the cache), added (to the cache), or updated,
- * the data is moved to the front of the list to depict itself as the most-recently-used data. The
- * LRU data is always at the end of the list.
+ * Data structure/implementation of the application's cache. The data structure
+ * consists of a hash table attached with a doubly linked-list. The linked-list
+ * helps in capturing and maintaining the LRU data in the cache. When a data is
+ * queried (from the cache), added (to the cache), or updated, the data is
+ * moved to the front of the list to depict itself as the most-recently-used
+ * data. The LRU data is always at the end of the list.
  */
 @Slf4j
 public class LruCache {
-
+  /**
+   * Static class Node.
+   */
   static class Node {
-    String userId;
-    UserAccount userAccount;
-    Node previous;
-    Node next;
+    /**
+     * user id.
+     */
+    private final String userId;
+    /**
+     * User Account.
+     */
+    private UserAccount userAccount;
+    /**
+     * previous.
+     */
+    private Node previous;
+    /**
+     * next.
+     */
+    private Node next;
 
-    public Node(String userId, UserAccount userAccount) {
-      this.userId = userId;
-      this.userAccount = userAccount;
+    /**
+     * Node definition.
+     *
+     * @param id      String
+     * @param account {@link UserAccount}
+     */
+    Node(final String id, final UserAccount account) {
+      this.userId = id;
+      this.userAccount = account;
     }
   }
 
-  int capacity;
-  Map<String, Node> cache = new HashMap<>();
-  Node head;
-  Node end;
+  /**
+   * Capacity of Cache.
+   */
+  private int capacity;
+  /**
+   * Cache {@link HashMap}.
+   */
+  private Map<String, Node> cache = new HashMap<>();
+  /**
+   * Head.
+   */
+  private Node head;
+  /**
+   * End.
+   */
+  private Node end;
 
-  public LruCache(int capacity) {
-    this.capacity = capacity;
+  /**
+   * Constructor.
+   *
+   * @param cap Integer.
+   */
+  public LruCache(final int cap) {
+    this.capacity = cap;
   }
 
   /**
    * Get user account.
+   *
+   * @param userId String
+   * @return {@link UserAccount}
    */
-  public UserAccount get(String userId) {
+  public UserAccount get(final String userId) {
     if (cache.containsKey(userId)) {
       var node = cache.get(userId);
       remove(node);
@@ -75,8 +117,10 @@ public class LruCache {
 
   /**
    * Remove node from linked list.
+   *
+   * @param node {@link Node}
    */
-  public void remove(Node node) {
+  public void remove(final Node node) {
     if (node.previous != null) {
       node.previous.next = node.next;
     } else {
@@ -91,8 +135,10 @@ public class LruCache {
 
   /**
    * Move node to the front of the list.
+   *
+   * @param node {@link Node}
    */
-  public void setHead(Node node) {
+  public void setHead(final Node node) {
     node.next = head;
     node.previous = null;
     if (head != null) {
@@ -106,8 +152,11 @@ public class LruCache {
 
   /**
    * Set user account.
+   *
+   * @param userAccount {@link UserAccount}
+   * @param userId      {@link String}
    */
-  public void set(String userId, UserAccount userAccount) {
+  public void set(final String userId, final UserAccount userAccount) {
     if (cache.containsKey(userId)) {
       var old = cache.get(userId);
       old.userAccount = userAccount;
@@ -127,25 +176,43 @@ public class LruCache {
     }
   }
 
-  public boolean contains(String userId) {
+  /**
+   * Check if Cache contains the userId.
+   *
+   * @param userId {@link String}
+   * @return boolean
+   */
+  public boolean contains(final String userId) {
     return cache.containsKey(userId);
   }
 
   /**
    * Invalidate cache for user.
+   *
+   * @param userId {@link String}
    */
-  public void invalidate(String userId) {
+  public void invalidate(final String userId) {
     var toBeRemoved = cache.remove(userId);
     if (toBeRemoved != null) {
-      LOGGER.info("# {} has been updated! Removing older version from cache...", userId);
+      LOGGER.info("# {} has been updated! "
+              + "Removing older version from cache...", userId);
       remove(toBeRemoved);
     }
   }
 
+  /**
+   * Check if the cache is full.
+   * @return boolean
+   */
   public boolean isFull() {
     return cache.size() >= capacity;
   }
 
+  /**
+   * Get LRU data.
+   *
+   * @return {@link UserAccount}
+   */
   public UserAccount getLruData() {
     return end.userAccount;
   }
@@ -161,6 +228,8 @@ public class LruCache {
 
   /**
    * Returns cache data in list form.
+   *
+   * @return {@link List}
    */
   public List<UserAccount> getCacheDataInListForm() {
     var listOfCacheData = new ArrayList<UserAccount>();
@@ -174,10 +243,14 @@ public class LruCache {
 
   /**
    * Set cache capacity.
+   *
+   * @param newCapacity int
    */
-  public void setCapacity(int newCapacity) {
+  public void setCapacity(final int newCapacity) {
     if (capacity > newCapacity) {
-      clear(); // Behavior can be modified to accommodate for decrease in cache size. For now, we'll
+      // Behavior can be modified to accommodate
+      // for decrease in cache size. For now, we'll
+      clear();
       // just clear the cache.
     } else {
       this.capacity = newCapacity;