Addressed checkstyle issue

Fix redundant list alloc in LotteryNumbers

CODE_COVERAGE.md

@@ -1,7 +1,7 @@
 # Code Coverage Report generation
 
 To generate the code coverage report, execute the following command:
-> mvn clean verify
+> mvn clean verify jacoco:report
 
 This will generate code coverage report in each of the modules. In order to view the same, open the following file in your browser.
 > target/site/jacoco/index.html 

README.md

@@ -8,7 +8,6 @@
 [![License MIT](https://img.shields.io/badge/license-MIT-blue.svg)](https://raw.githubusercontent.com/iluwatar/java-design-patterns/master/LICENSE.md)
 [![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)
 [![Quality Gate](https://sonarcloud.io/api/project_badges/measure?project=com.iluwatar%3Ajava-design-patterns&metric=alert_status)](https://sonarcloud.io/dashboard/index/com.iluwatar%3Ajava-design-patterns)
-[![CII Best Practices](https://bestpractices.coreinfrastructure.org/projects/1503/badge)](https://bestpractices.coreinfrastructure.org/projects/1503)
 
 # Introduction
 

abstract-document/pom.xml

@@ -29,7 +29,7 @@
     <parent>
         <artifactId>java-design-patterns</artifactId>
         <groupId>com.iluwatar</groupId>
-        <version>1.19.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
     <artifactId>abstract-document</artifactId>
     <dependencies>

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

@@ -32,6 +32,7 @@ import java.util.stream.Stream;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 /**
  * AbstractDocument test class
@@ -81,8 +82,8 @@ public class AbstractDocumentTest {
     Map<String, Object> props = new HashMap<>();
     props.put(KEY, VALUE);
     DocumentImplementation document = new DocumentImplementation(props);
-    assertNotNull(document.toString().contains(KEY));
-    assertNotNull(document.toString().contains(VALUE));
+    assertTrue(document.toString().contains(KEY));
+    assertTrue(document.toString().contains(VALUE));
   }
 
 }

abstract-factory/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.19.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>abstract-factory</artifactId>
   <dependencies>

acyclic-visitor/README.md

@@ -0,0 +1,39 @@
+---
+layout: pattern
+title: Acyclic Visitor
+folder: acyclic-visitor
+permalink: /patterns/acyclic-visitor/
+categories: Behavioral
+tags:
+ - Java
+ - Difficulty-Intermediate
+---
+
+![alt text](./etc/acyclic-visitor.png "Acyclic Visitor")
+
+## Intent
+Allow new functions to be added to existing class hierarchies without affecting those hierarchies, and without creating the troublesome dependency cycles that are inherent to the GOF VISITOR Pattern.
+
+## Applicability
+This pattern can be used:
+* When you need to add a new function to an existing hierarchy without the need to alter or affect that hierarchy.
+* When there are functions that operate upon a hierarchy, but which do not belong in the hierarchy itself. e.g. the ConfigureForDOS / ConfigureForUnix / ConfigureForX issue.
+* When you need to perform very different operations on an object depending upon its type.
+* When the visited class hierarchy will be frequently extended with new derivatives of the Element class.
+* When the recompilation, relinking, retesting or redistribution of the derivatives of Element is very expensive.
+
+## Consequences
+The good:
+* No dependency cycles between class hierarchies.
+* No need to recompile all the visitors if a new one is added.
+* Does not cause compilation failure in existing visitors if class hierarchy has a new member.
+
+The bad:
+* Violates the principle of least surprise or Liskov's Substitution principle by showing that it can accept all visitors but actually only being interested in particular visitors.
+* Parallel hierarchy of visitors has to be created for all members in visitable class hierarchy.
+
+## Related patterns
+* [Visitor Pattern](../visitor/README.md)
+
+## Credits
+* [Acyclic Visitor](http://condor.depaul.edu/dmumaugh/OOT/Design-Principles/acv.pdf)

acyclic-visitor/etc/Acyclic Visitor.ucls

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

acyclic-visitor/pom.xml

@@ -0,0 +1,76 @@
+<!--
+
+    The MIT License
+    Copyright (c) 2014 Ilkka Seppälä
+
+    Permission is hereby granted, free of charge, to any person obtaining a copy
+    of this software and associated documentation files (the "Software"), to deal
+    in the Software without restriction, including without limitation the rights
+    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+    copies of the Software, and to permit persons to whom the Software is
+    furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included in
+    all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+    THE SOFTWARE.
+
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+	
+	<parent>
+		<groupId>com.iluwatar</groupId>
+		<artifactId>java-design-patterns</artifactId>
+		<version>1.21.0-SNAPSHOT</version>
+	</parent>
+	
+	<artifactId>acyclic-visitor</artifactId>
+
+	<properties>
+		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+		<maven.compiler.source>1.8</maven.compiler.source>
+		<maven.compiler.target>1.8</maven.compiler.target>
+	</properties>
+
+	<dependencies>
+		<!-- https://mvnrepository.com/artifact/org.assertj/assertj-core -->
+		<dependency>
+			<groupId>org.assertj</groupId>
+			<artifactId>assertj-core</artifactId>
+			<version>3.9.1</version>
+			<scope>test</scope>
+		</dependency>
+		<!-- https://mvnrepository.com/artifact/uk.org.lidalia/slf4j-test -->
+		<dependency>
+			<groupId>uk.org.lidalia</groupId>
+			<artifactId>slf4j-test</artifactId>
+			<version>1.0.0</version>
+			<scope>test</scope>
+		</dependency>
+		<dependency>
+      		<groupId>org.junit.jupiter</groupId>
+      		<artifactId>junit-jupiter-api</artifactId>
+      		<scope>test</scope>
+    	</dependency>
+    	<dependency>
+      		<groupId>org.junit.jupiter</groupId>
+      		<artifactId>junit-jupiter-engine</artifactId>
+      		<scope>test</scope>
+    	</dependency>
+		<dependency>
+			<groupId>org.mockito</groupId>
+			<artifactId>mockito-all</artifactId>
+			<version>1.9.5</version>
+			<scope>test</scope>
+		</dependency>
+	</dependencies>
+</project>

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

@@ -0,0 +1,31 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 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.acyclicvisitor;
+
+/**
+ * All ModemVisitor interface extends all visitor interfaces. This interface
+ * provides ease of use when a visitor needs to visit all modem types.
+ */
+public interface AllModemVisitor extends ZoomVisitor, HayesVisitor{
+
+}

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

@@ -0,0 +1,55 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 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.acyclicvisitor;
+
+/**
+ * The Acyclic Visitor pattern allows new functions to be added to existing class 
+ * hierarchies without affecting those hierarchies, and without creating the dependency 
+ * cycles that are inherent to the GoF Visitor pattern, by making the Visitor base class 
+ * degenerate
+ * <p>
+ * In this example the visitor base class is {@link ModemVisitor}. The base class of the 
+ * visited hierarchy is {@link Modem} and has two children {@link Hayes} and {@link Zoom} 
+ * each one having its own visitor interface {@link HayesVisitor} and {@link ZoomVisitor} 
+ * respectively. {@link ConfigureForUnixVisitor} and {@link ConfigureForDosVisitor} 
+ * implement each derivative's visit method only if it is required 
+ */
+public class App {
+  
+  /**
+   * Program's entry point
+   */
+  
+  public static void main(String[] args) {  
+    ConfigureForUnixVisitor conUnix = new ConfigureForUnixVisitor();
+    ConfigureForDosVisitor conDos = new ConfigureForDosVisitor();
+    
+    Zoom zoom = new Zoom();
+    Hayes hayes = new Hayes();
+    
+    hayes.accept(conDos); // Hayes modem with Unix configurator
+    zoom.accept(conDos); // Zoom modem with Dos configurator
+    hayes.accept(conUnix); // Hayes modem with Unix configurator
+    zoom.accept(conUnix); // Zoom modem with Unix configurator   
+  }
+}

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

@@ -0,0 +1,43 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 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.acyclicvisitor;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * ConfigureForDosVisitor class implements both zoom's and  hayes' visit method 
+ * for Dos manufacturer
+ */
+public class ConfigureForDosVisitor implements AllModemVisitor {
+
+  private static final Logger LOGGER = LoggerFactory.getLogger(ConfigureForDosVisitor.class);
+
+  public void visit(Hayes hayes) {
+    LOGGER.info(hayes + " used with Dos configurator.");
+  }
+
+  public void visit(Zoom zoom) {
+    LOGGER.info(zoom + " used with Dos configurator.");
+  }
+}

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

@@ -0,0 +1,40 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 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.acyclicvisitor;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * ConfigureForUnixVisitor class implements zoom's visit method for Unix 
+ * manufacturer, unlike traditional visitor pattern, this class may selectively implement
+ * visit for other modems.
+ */
+public class ConfigureForUnixVisitor implements ZoomVisitor {
+
+  private static final Logger LOGGER = LoggerFactory.getLogger(ConfigureForUnixVisitor.class);
+
+  public void visit(Zoom zoom) {
+    LOGGER.info(zoom + " used with Unix configurator.");
+  }
+}

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

@@ -0,0 +1,56 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 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.acyclicvisitor;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Hayes class implements its accept method
+ */
+public class Hayes extends Modem {
+  
+  private static final Logger LOGGER = LoggerFactory.getLogger(ConfigureForDosVisitor.class);
+
+  /**
+   * Accepts all visitors but honors only HayesVisitor
+   */
+  @Override
+  public void accept(ModemVisitor modemVisitor) {
+    if (modemVisitor instanceof HayesVisitor) {
+      ((HayesVisitor) modemVisitor).visit(this);
+    } else {
+      LOGGER.info("Only HayesVisitor is allowed to visit Hayes modem");
+    }
+
+  }
+  
+  /**
+   * Hayes' modem's toString
+   * method
+   */
+  @Override
+  public String toString() {
+    return "Hayes modem";
+  }
+}

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

@@ -0,0 +1,30 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 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.acyclicvisitor;
+
+/**
+ * HayesVisitor interface
+ */
+public interface HayesVisitor extends ModemVisitor {
+  void visit(Hayes hayes);
+}

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

@@ -0,0 +1,30 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 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.acyclicvisitor;
+
+/**
+ * Modem abstract class
+ */
+public abstract class Modem {
+  public abstract void accept(ModemVisitor modemVisitor);
+}

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

@@ -0,0 +1,32 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 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.acyclicvisitor;
+
+/**
+ * ModemVisitor interface does not contain any visit methods so that it does not
+ * depend on the visited hierarchy. Each derivative's visit method is declared in 
+ * its own visitor interface
+ */
+public interface ModemVisitor {
+  // Visitor is a degenerate base class for all visitors.
+}

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

@@ -0,0 +1,55 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 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.acyclicvisitor;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Zoom class implements its accept method
+ */
+public class Zoom extends Modem {
+  
+  private static final Logger LOGGER = LoggerFactory.getLogger(ConfigureForDosVisitor.class);
+
+  /**
+   * Accepts all visitors but honors only ZoomVisitor
+   */
+  @Override
+  public void accept(ModemVisitor modemVisitor) {
+    if (modemVisitor instanceof  ZoomVisitor) {
+      ((ZoomVisitor) modemVisitor).visit(this);
+    } else {
+      LOGGER.info("Only ZoomVisitor is allowed to visit Zoom modem");
+    }
+  }
+  
+  /**
+   * Zoom modem's toString
+   * method
+   */
+  @Override
+  public String toString() {
+    return "Zoom modem";
+  }
+}

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

@@ -20,16 +20,11 @@
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */
-package com.iluwatar.iterator;
+package com.iluwatar.acyclicvisitor;
 
 /**
- * 
- * ItemIterator interface.
- * 
+ * ZoomVisitor interface
  */
-public interface ItemIterator {
-
-  boolean hasNext();
-
-  Item next();
+public interface ZoomVisitor extends ModemVisitor {
+  void visit(Zoom zoom);
 }

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

@@ -0,0 +1,39 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 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.acyclicvisitor;
+
+import org.junit.jupiter.api.Test;
+
+import com.iluwatar.acyclicvisitor.App;
+
+/**
+ * Tests that the Acyclic Visitor example runs without errors.
+ */
+public class AppTest {
+  
+  @Test
+  public void test() {
+    String[] args = {};
+    App.main(args);  
+  }
+}

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

@@ -0,0 +1,75 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 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.acyclicvisitor;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.groups.Tuple.tuple;
+import static org.mockito.Mockito.mock;
+import static uk.org.lidalia.slf4jext.Level.INFO;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.Test;
+
+import com.iluwatar.acyclicvisitor.ConfigureForDosVisitor;
+import com.iluwatar.acyclicvisitor.Hayes;
+import com.iluwatar.acyclicvisitor.HayesVisitor;
+import com.iluwatar.acyclicvisitor.Zoom;
+import com.iluwatar.acyclicvisitor.ZoomVisitor;
+
+import uk.org.lidalia.slf4jtest.TestLogger;
+import uk.org.lidalia.slf4jtest.TestLoggerFactory;
+
+/**
+ * ConfigureForDosVisitor test class
+ */
+public class ConfigureForDosVisitorTest {
+
+  TestLogger logger = TestLoggerFactory.getTestLogger(ConfigureForDosVisitor.class);
+  
+  @Test
+  public void testVisitForZoom() {    
+    ConfigureForDosVisitor conDos = new ConfigureForDosVisitor();
+    Zoom zoom = new Zoom();
+    
+    conDos.visit(zoom);
+    
+    assertThat(logger.getLoggingEvents()).extracting("level", "message").contains(
+        tuple(INFO, zoom + " used with Dos configurator."));
+  }
+  
+  @Test
+  public void testVisitForHayes() {
+    ConfigureForDosVisitor conDos = new ConfigureForDosVisitor();
+    Hayes hayes = new Hayes();
+    
+    conDos.visit(hayes);
+    
+    assertThat(logger.getLoggingEvents()).extracting("level", "message").contains(
+        tuple(INFO, hayes + " used with Dos configurator."));
+  }
+  
+  @AfterEach
+  public void clearLoggers() {
+    TestLoggerFactory.clear();
+  }
+}

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

@@ -0,0 +1,57 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 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.acyclicvisitor;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.groups.Tuple.tuple;
+import static uk.org.lidalia.slf4jext.Level.INFO;
+
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.Test;
+
+import uk.org.lidalia.slf4jtest.TestLogger;
+import uk.org.lidalia.slf4jtest.TestLoggerFactory;
+
+/**
+ * ConfigureForUnixVisitor test class
+ */
+public class ConfigureForUnixVisitorTest {
+  
+  private static final TestLogger LOGGER = TestLoggerFactory.getTestLogger(ConfigureForUnixVisitor.class);
+  
+  @AfterEach
+  public void clearLoggers() {
+    TestLoggerFactory.clear();
+  }
+  
+  @Test
+  public void testVisitForZoom() {
+    ConfigureForUnixVisitor conUnix = new ConfigureForUnixVisitor();
+    Zoom zoom = new Zoom();
+    
+    conUnix.visit(zoom);
+    
+    assertThat(LOGGER.getLoggingEvents()).extracting("level", "message").contains(
+        tuple(INFO, zoom + " used with Unix configurator."));
+  }
+}

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

@@ -0,0 +1,60 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 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.acyclicvisitor;
+
+import static org.mockito.Matchers.eq;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.verifyZeroInteractions;
+
+import org.junit.jupiter.api.Test;
+
+import com.iluwatar.acyclicvisitor.ConfigureForDosVisitor;
+import com.iluwatar.acyclicvisitor.ConfigureForUnixVisitor;
+import com.iluwatar.acyclicvisitor.Hayes;
+import com.iluwatar.acyclicvisitor.HayesVisitor;
+
+/**
+ * Hayes test class
+ */
+public class HayesTest {
+
+  @Test
+  public void testAcceptForDos() {  
+    Hayes hayes = new Hayes();
+    ConfigureForDosVisitor mockVisitor = mock(ConfigureForDosVisitor.class);
+    
+    hayes.accept(mockVisitor);
+    verify((HayesVisitor)mockVisitor).visit(eq(hayes));
+  }
+  
+  @Test
+  public void testAcceptForUnix() {    
+    Hayes hayes = new Hayes();
+    ConfigureForUnixVisitor mockVisitor = mock(ConfigureForUnixVisitor.class);
+    
+    hayes.accept(mockVisitor);
+    
+    verifyZeroInteractions(mockVisitor);
+  }
+}

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

@@ -0,0 +1,59 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 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.acyclicvisitor;
+
+
+import static org.mockito.Matchers.eq;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.mock;
+
+import org.junit.jupiter.api.Test;
+
+import com.iluwatar.acyclicvisitor.ConfigureForDosVisitor;
+import com.iluwatar.acyclicvisitor.ConfigureForUnixVisitor;
+import com.iluwatar.acyclicvisitor.Zoom;
+import com.iluwatar.acyclicvisitor.ZoomVisitor;
+
+/**
+ * Zoom test class
+ */
+public class ZoomTest {
+  
+  @Test
+  public void testAcceptForDos() {  
+    Zoom zoom = new Zoom();
+    ConfigureForDosVisitor mockVisitor = mock(ConfigureForDosVisitor.class);
+    
+    zoom.accept(mockVisitor);
+    verify((ZoomVisitor)mockVisitor).visit(eq(zoom));
+  }
+  
+  @Test
+  public void testAcceptForUnix() {
+    Zoom zoom = new Zoom();
+    ConfigureForUnixVisitor mockVisitor = mock(ConfigureForUnixVisitor.class);
+    
+    zoom.accept(mockVisitor);
+    verify((ZoomVisitor)mockVisitor).visit(eq(zoom));
+  }
+}

adapter/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.19.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>adapter</artifactId>
   <dependencies>

aggregator-microservices/aggregator-service/pom.xml

@@ -29,7 +29,7 @@
     <parent>
         <artifactId>aggregator-microservices</artifactId>
         <groupId>com.iluwatar</groupId>
-        <version>1.19.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
     <modelVersion>4.0.0</modelVersion>
 

aggregator-microservices/information-microservice/pom.xml

@@ -29,7 +29,7 @@
     <parent>
         <artifactId>aggregator-microservices</artifactId>
         <groupId>com.iluwatar</groupId>
-        <version>1.19.0</version>
+        <version>1.21.0-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>1.19.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
     <modelVersion>4.0.0</modelVersion>
 

aggregator-microservices/inventory-microservice/src/test/java/com/iluwatar/inventory/microservice/InventoryControllerTest.java

@@ -31,7 +31,7 @@ import static org.junit.jupiter.api.Assertions.assertEquals;
  */
 public class InventoryControllerTest {
   @Test
-  public void testGetProductInventories() throws Exception {
+  public void testGetProductInventories() {
     InventoryController inventoryController = new InventoryController();
 
     int numberOfInventories = inventoryController.getProductInventories();

aggregator-microservices/pom.xml

@@ -29,7 +29,7 @@
     <parent>
         <artifactId>java-design-patterns</artifactId>
         <groupId>com.iluwatar</groupId>
-        <version>1.19.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
     <modelVersion>4.0.0</modelVersion>
     <artifactId>aggregator-microservices</artifactId>

ambassador/README.md

@@ -0,0 +1,178 @@
+---
+layout: pattern
+title: Ambassador
+folder: ambassador
+permalink: /patterns/ambassador/
+categories: Structural
+tags:
+ - Java
+ - Difficulty-Intermediate
+---
+
+## Intent
+Provide a helper service instance on a client and offload common functionality away from a shared resource.
+
+## Explanation
+Real world example
+
+> A remote service has many clients accessing a function it provides. The service is a legacy application and is impossible to update. Large numbers of requests from users are causing connectivity issues. New rules for request frequency should be implemented along with latency checks and client-side logging.
+
+In plain words
+
+> Using the ambassador pattern, we can implement less-frequent polling from clients along with latency checks and logging.
+
+Microsoft documentation states
+
+> An ambassador service can be thought of as an out-of-process proxy that is co-located with the client.
+  This pattern can be useful for offloading common client connectivity tasks such as monitoring, logging, routing, security (such as TLS), and resiliency patterns in a language agnostic way. It is often used with legacy applications, or other applications that are difficult to modify, in order to extend their networking capabilities. It can also enable a specialized team to implement those features.
+
+**Programmatic Example**
+
+With the above example in mind we will imitate the functionality in a simple manner. We have an interface implemented by the remote service as well as the ambassador service:
+
+```java
+interface RemoteServiceInterface {
+
+    long doRemoteFunction(int value) throws Exception;
+}
+```
+
+A remote services represented as a singleton.
+
+```java
+public class RemoteService implements RemoteServiceInterface {
+
+		private static final Logger LOGGER = LoggerFactory.getLogger(RemoteService.class);
+    private static RemoteService service = null;2
+
+    static synchronized RemoteService getRemoteService() {
+        if (service == null) {
+            service = new RemoteService();
+        }
+        return service;
+    }
+
+    private RemoteService() {}
+
+    @Override
+    public long doRemoteFunction(int value) {
+
+        long waitTime = (long) Math.floor(Math.random() * 1000);
+
+        try {
+            sleep(waitTime);
+        } catch (InterruptedException e) {
+            LOGGER.error("Thread sleep interrupted", e)
+        }
+        return waitTime >= 200 ? value * 10 : -1;
+    }
+}
+```
+
+A service ambassador adding additional features such as logging, latency checks
+
+```java
+public class ServiceAmbassador implements RemoteServiceInterface {
+
+    private static final Logger LOGGER = LoggerFactory.getLogger(ServiceAmbassador.class);
+    private static final int RETRIES = 3;
+    private static final int DELAY_MS = 3000;
+
+    ServiceAmbassador() {}
+
+    @Override
+    public long doRemoteFunction(int value) {
+
+        return safeCall(value);
+    }
+
+    private long checkLatency(int value) {
+        RemoteService service = RemoteService.getRemoteService();
+        long startTime = System.currentTimeMillis();
+        long result = service.doRemoteFunction(value);
+        long timeTaken = System.currentTimeMillis() - startTime;
+
+        LOGGER.info("Time taken (ms): " + timeTaken);
+        return result;
+    }
+
+    private long safeCall(int value) {
+
+        int retries = 0;
+        long result = -1;
+
+        for (int i = 0; i < RETRIES; i++) {
+
+            if (retries >= RETRIES) {
+                return -1;
+            }
+
+            if ((result = checkLatency(value)) == -1) {
+                LOGGER.info("Failed to reach remote: (" + (i + 1) + ")");
+                retries++;
+                try {
+                    sleep(DELAY_MS);
+                } catch (InterruptedException e) {
+                    LOGGER.error("Thread sleep state interrupted", e);
+                }
+            } else {
+                break;
+            }
+        }
+        return result;
+    }
+}
+```
+
+A client has a local service ambassador used to interact with the remote service:
+
+```java
+public class Client {
+
+    private ServiceAmbassador serviceAmbassador;
+
+    Client() {
+        serviceAmbassador = new ServiceAmbassador();
+    }
+
+    long useService(int value) {
+        long result = serviceAmbassador.doRemoteFunction(value);
+        LOGGER.info("Service result: " + result)
+        return result;
+    }
+}
+```
+
+And here are two clients using the service.
+
+```java
+Client host1 = new Client();
+Client host2 = new Client();
+host1.useService(12);
+host2.useService(73);
+```
+
+## Applicability
+Ambassador is applicable when working with a legacy remote service that cannot
+be modified or would be extremely difficult to modify. Connectivity features can
+be implemented on the client avoiding the need for changes on the remote service.
+
+* Ambassador provides a local interface for a remote service.
+* Ambassador provides logging, circuit breaking, retries and security on the client.
+
+## Typical Use Case
+
+* Control access to another object
+* Implement logging
+* Implement circuit breaking
+* Offload remote service tasks
+* Facilitate network connection
+
+## Real world examples
+
+* [Kubernetes-native API gateway for microservices](https://github.com/datawire/ambassador)
+
+## Credits
+
+* [Ambassador pattern](https://docs.microsoft.com/en-us/azure/architecture/patterns/ambassador)
+* [Designing Distributed Systems: Patterns and Paradigms for Scalable, Reliable Services](https://books.google.co.uk/books?id=6BJNDwAAQBAJ&pg=PT35&lpg=PT35&dq=ambassador+pattern+in+real+world&source=bl&ots=d2e7GhYdHi&sig=Lfl_MDnCgn6lUcjzOg4GXrN13bQ&hl=en&sa=X&ved=0ahUKEwjk9L_18rrbAhVpKcAKHX_KA7EQ6AEIWTAI#v=onepage&q=ambassador%20pattern%20in%20real%20world&f=false)

ambassador/pom.xml

@@ -0,0 +1,48 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+
+    The MIT License
+    Copyright (c) 2014-2016 Ilkka Seppälä
+
+    Permission is hereby granted, free of charge, to any person obtaining a copy
+    of this software and associated documentation files (the "Software"), to deal
+    in the Software without restriction, including without limitation the rights
+    to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+    copies of the Software, and to permit persons to whom the Software is
+    furnished to do so, subject to the following conditions:
+
+    The above copyright notice and this permission notice shall be included in
+    all copies or substantial portions of the Software.
+
+    THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+    IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+    FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+    AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+    LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+    OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+    THE SOFTWARE.
+
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <parent>
+    <artifactId>java-design-patterns</artifactId>
+    <groupId>com.iluwatar</groupId>
+    <version>1.21.0-SNAPSHOT</version>
+  </parent>
+  <modelVersion>4.0.0</modelVersion>
+  <artifactId>ambassador</artifactId>
+  <dependencies>
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-api</artifactId>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-engine</artifactId>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+</project>

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

@@ -0,0 +1,53 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 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.ambassador;
+
+/**
+ *
+ * The ambassador pattern creates a helper service that sends network requests on behalf of a
+ * client. It is often used in cloud-based applications to offload features of a remote service.
+ *
+ * An ambassador service can be thought of as an out-of-process proxy that is co-located with
+ * the client. Similar to the proxy design pattern, the ambassador service provides an interface
+ * for another remote service. In addition to the interface, the ambassador provides extra
+ * functionality and features, specifically offloaded common connectivity tasks. This usually
+ * consists of monitoring, logging, routing, security etc. This is extremely useful in
+ * legacy applications where the codebase is difficult to modify and allows for improvements
+ * in the application's networking capabilities.
+ *
+ * In this example, we will the ({@link ServiceAmbassador}) class represents the ambassador while the
+ * ({@link RemoteService}) class represents a remote application.
+ *
+ */
+public class App {
+
+  /**
+  * Entry point
+  */
+  public static void main(String[] args) {
+    Client host1 = new Client();
+    Client host2 = new Client();
+    host1.useService(12);
+    host2.useService(73);
+  }
+}

ambassador/src/main/java/com/iluwatar/ambassador/Client.java

@@ -0,0 +1,42 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 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.ambassador;
+
+import org.slf4j.LoggerFactory;
+
+import org.slf4j.Logger;
+
+/**
+ * A simple Client
+ */
+public class Client {
+
+  private static final Logger LOGGER = LoggerFactory.getLogger(Client.class);
+  private final ServiceAmbassador serviceAmbassador = new ServiceAmbassador();
+
+  long useService(int value) {
+    long result = serviceAmbassador.doRemoteFunction(value);
+    LOGGER.info("Service result: " + result);
+    return result;
+  }
+}

ambassador/src/main/java/com/iluwatar/ambassador/RemoteService.java

@@ -0,0 +1,65 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 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.ambassador;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import static java.lang.Thread.sleep;
+
+/**
+ * A remote legacy application represented by a Singleton implementation.
+ */
+public class RemoteService implements RemoteServiceInterface {
+
+  private static final Logger LOGGER = LoggerFactory.getLogger(RemoteService.class);
+  private static RemoteService service = null;
+
+  static synchronized RemoteService getRemoteService() {
+    if (service == null) {
+      service = new RemoteService();
+    }
+    return service;
+  }
+
+  private RemoteService() {}
+
+  /**
+   * Remote function takes a value and multiplies it by 10 taking a random amount of time.
+   * Will sometimes return -1. This imitates connectivity issues a client might have to account for.
+   * @param value integer value to be multiplied.
+   * @return if waitTime is more than 200ms, it returns value * 10, otherwise -1.
+   */
+  @Override
+  public long doRemoteFunction(int value) {
+
+    long waitTime = (long) Math.floor(Math.random() * 1000);
+
+    try {
+      sleep(waitTime);
+    } catch (InterruptedException e) {
+      LOGGER.error("Thread sleep state interrupted", e);
+    }
+    return waitTime >= 200 ? value * 10 : -1;
+  }
+}

ambassador/src/main/java/com/iluwatar/ambassador/RemoteServiceInterface.java

@@ -0,0 +1,31 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 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.ambassador;
+
+/**
+ * Interface shared by ({@link RemoteService}) and ({@link ServiceAmbassador}).
+ */
+interface RemoteServiceInterface {
+    
+  long doRemoteFunction(int value) throws Exception;
+}

ambassador/src/main/java/com/iluwatar/ambassador/ServiceAmbassador.java

@@ -0,0 +1,84 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 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.ambassador;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import static java.lang.Thread.sleep;
+
+/**
+ *
+ * ServiceAmbassador provides an interface for a ({@link Client}) to access ({@link RemoteService}).
+ * The interface adds logging, latency testing and usage of the service in a safe way that will not
+ * add stress to the remote service when connectivity issues occur.
+ *
+ */
+public class ServiceAmbassador implements RemoteServiceInterface {
+
+  private static final Logger LOGGER = LoggerFactory.getLogger(ServiceAmbassador.class);
+  private static final int RETRIES = 3;
+  private static final int DELAY_MS = 3000;
+
+  ServiceAmbassador() {}
+
+  @Override
+  public long doRemoteFunction(int value) {
+    return safeCall(value);
+  }
+
+  private long checkLatency(int value) {
+    long startTime = System.currentTimeMillis();
+    long result = RemoteService.getRemoteService().doRemoteFunction(value);
+    long timeTaken = System.currentTimeMillis() - startTime;
+
+    LOGGER.info("Time taken (ms): " + timeTaken);
+    return result;
+  }
+
+  private long safeCall(int value) {
+
+    int retries = 0;
+    long result = -1;
+
+    for (int i = 0; i < RETRIES; i++) {
+
+      if (retries >= RETRIES) {
+        return -1;
+      }
+
+      if ((result = checkLatency(value)) == -1) {
+        LOGGER.info("Failed to reach remote: (" + (i + 1) + ")");
+        retries++;
+        try {
+          sleep(DELAY_MS);
+        } catch (InterruptedException e) {
+          LOGGER.error("Thread sleep state interrupted", e);
+        }
+      } else {
+        break;
+      }
+    }
+    return result;
+  }
+}

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

@@ -0,0 +1,36 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 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.ambassador;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Application test
+ */
+public class AppTest {
+
+  @Test
+  public void test() {
+    App.main(new String[]{});
+  }
+}

ambassador/src/test/java/com/iluwatar/ambassador/ClientTest.java

@@ -0,0 +1,40 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 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.ambassador;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Test for {@link Client}
+ */
+public class ClientTest {
+
+  @Test
+  public void test() {
+
+    Client client = new Client();
+    long result = client.useService(10);
+
+    assert result == 100 || result == -1;
+  }
+}

ambassador/src/test/java/com/iluwatar/ambassador/RemoteServiceTest.java

@@ -0,0 +1,37 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 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.ambassador;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Test for {@link RemoteService}
+ */
+public class RemoteServiceTest {
+
+  @Test
+  public void test() {
+    long result = RemoteService.getRemoteService().doRemoteFunction(10);
+    assert result == 100 || result == -1;
+  }
+}

ambassador/src/test/java/com/iluwatar/ambassador/ServiceAmbassadorTest.java

@@ -0,0 +1,37 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 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.ambassador;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Test for {@link ServiceAmbassador}
+ */
+public class ServiceAmbassadorTest {
+
+  @Test
+  public void test() {
+    long result = new ServiceAmbassador().doRemoteFunction(10);
+    assert result == 100 || result == -1;
+  }
+}

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

@@ -29,7 +29,7 @@
   <parent>
     <artifactId>api-gateway</artifactId>
     <groupId>com.iluwatar</groupId>
-    <version>1.19.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <modelVersion>4.0.0</modelVersion>
   <artifactId>api-gateway-service</artifactId>

api-gateway/image-microservice/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <artifactId>api-gateway</artifactId>
     <groupId>com.iluwatar</groupId>
-    <version>1.19.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
 
   <modelVersion>4.0.0</modelVersion>

api-gateway/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <artifactId>java-design-patterns</artifactId>
     <groupId>com.iluwatar</groupId>
-    <version>1.19.0</version>
+    <version>1.21.0-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>1.19.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
 
   <modelVersion>4.0.0</modelVersion>

async-method-invocation/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.19.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>async-method-invocation</artifactId>
   <dependencies>

balking/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <artifactId>java-design-patterns</artifactId>
     <groupId>com.iluwatar</groupId>
-    <version>1.19.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <modelVersion>4.0.0</modelVersion>
 

bridge/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.19.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>bridge</artifactId>
   <dependencies>

bridge/src/test/java/com/iluwatar/bridge/HammerTest.java

@@ -37,7 +37,7 @@ public class HammerTest extends WeaponTest {
    * underlying weapon implementation.
    */
   @Test
-  public void testHammer() throws Exception {
+  public void testHammer() {
     final Hammer hammer = spy(new Hammer(mock(FlyingEnchantment.class)));
     testBasicWeaponActions(hammer);
   }

bridge/src/test/java/com/iluwatar/bridge/SwordTest.java

@@ -37,7 +37,7 @@ public class SwordTest extends WeaponTest {
    * underlying weapon implementation.
    */
   @Test
-  public void testSword() throws Exception {
+  public void testSword() {
     final Sword sword = spy(new Sword(mock(FlyingEnchantment.class)));
     testBasicWeaponActions(sword);
   }

builder/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.19.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>builder</artifactId>
   <dependencies>

business-delegate/pom.xml

@@ -30,7 +30,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>java-design-patterns</artifactId>
-		<version>1.19.0</version>
+		<version>1.21.0-SNAPSHOT</version>
 	</parent>
 	<artifactId>business-delegate</artifactId>
 	<dependencies>

caching/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.19.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>caching</artifactId>
   <dependencies>

callback/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.19.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>callback</artifactId>
   <dependencies>

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

@@ -41,12 +41,7 @@ public class App {
    */
   public static void main(String[] args) {
     Task task = new SimpleTask();
-    Callback callback = new Callback() {
-      @Override
-      public void call() {
-        LOGGER.info("I'm done now.");
-      }
-    };
+    Callback callback = () -> LOGGER.info("I'm done now.");
     task.executeWith(callback);
   }
 }

callback/src/test/java/com/iluwatar/callback/CallbackTest.java

@@ -38,29 +38,6 @@ public class CallbackTest {
 
   @Test
   public void test() {
-    Callback callback = new Callback() {
-      @Override
-      public void call() {
-        callingCount++;
-      }
-    };
-
-    Task task = new SimpleTask();
-
-    assertEquals(new Integer(0), callingCount, "Initial calling count of 0");
-
-    task.executeWith(callback);
-
-    assertEquals(new Integer(1), callingCount, "Callback called once");
-
-    task.executeWith(callback);
-
-    assertEquals(new Integer(2), callingCount, "Callback called twice");
-
-  }
-
-  @Test
-  public void testWithLambdasExample() {
     Callback callback = () -> callingCount++;
 
     Task task = new SimpleTask();

chain/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.19.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>chain</artifactId>
   <dependencies>

chain/src/test/java/com/iluwatar/chain/OrcKingTest.java

@@ -43,7 +43,7 @@ public class OrcKingTest {
   };
 
   @Test
-  public void testMakeRequest() throws Exception {
+  public void testMakeRequest() {
     final OrcKing king = new OrcKing();
 
     for (final Request request : REQUESTS) {

collection-pipeline/README.md

@@ -0,0 +1,30 @@
+---
+layout: pattern
+title: Collection Pipeline
+folder: collection-pipeline
+permalink: /patterns/collection-pipeline/
+categories: Functional
+tags:
+ - Java
+ - Difficulty-Beginner
+ - Functional
+---
+
+## Intent
+Collection Pipeline introduces Function Composition and Collection Pipeline, two functional-style patterns that you can combine to iterate collections in your code. 
+In functional programming, it's common to sequence complex operations through a series of smaller modular functions or operations. The series is called a composition of functions, or a function composition. When a collection of data flows through a function composition, it becomes a collection pipeline. Function Composition and Collection Pipeline are two design patterns frequently used in functional-style programming.
+
+![alt text](./etc/collection-pipeline.png "Collection Pipeline")
+
+## Applicability
+Use the Collection Pipeline pattern when
+
+* When you want to perform a sequence of operations where one operation's collected output is fed into the next
+* When you use a lot of statements in your code
+* When you use a lot of loops in your code
+
+## Credits
+
+* [Function composition and the Collection Pipeline pattern](https://www.ibm.com/developerworks/library/j-java8idioms2/index.html)
+* [Martin Fowler](https://martinfowler.com/articles/collection-pipeline/)
+* [Java8 Streams](https://docs.oracle.com/javase/8/docs/api/java/util/stream/package-summary.html)

collection-pipeline/etc/collection-pipeline.ucls

@@ -0,0 +1,98 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<class-diagram version="1.2.2" icons="true" always-add-relationships="false" generalizations="true" realizations="true" 
+  associations="true" dependencies="false" nesting-relationships="true" router="FAN">  
+  <class id="1" language="java" name="com.iluwatar.collectionpipeline.App" project="collection-pipeline" 
+    file="/collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/App.java" binary="false" 
+    corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="150" y="100"/>    
+    <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.collectionpipeline.ImperativeProgramming" 
+    project="collection-pipeline" 
+    file="/collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/ImperativeProgramming.java" binary="false" 
+    corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="437" y="109"/>    
+    <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.collectionpipeline.Car" project="collection-pipeline" 
+    file="/collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/Car.java" binary="false" 
+    corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="724" y="339"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="true" package="true" protected="true" private="true" static="true"/>      
+      <operations public="true" package="true" protected="true" private="true" static="true"/>    
+    </display>  
+  </class>  
+  <class id="4" language="java" name="com.iluwatar.collectionpipeline.CarFactory" project="collection-pipeline" 
+    file="/collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/CarFactory.java" binary="false" 
+    corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="899" y="91"/>    
+    <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="5" language="java" name="com.iluwatar.collectionpipeline.FunctionalProgramming" 
+    project="collection-pipeline" 
+    file="/collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/FunctionalProgramming.java" binary="false" 
+    corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="1187" y="109"/>    
+    <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="6" language="java" name="com.iluwatar.collectionpipeline.Category" project="collection-pipeline" 
+    file="/collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/Category.java" binary="false" 
+    corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="486" y="339"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="true" 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>  
+  <class id="7" language="java" name="com.iluwatar.collectionpipeline.Person" project="collection-pipeline" 
+    file="/collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/Person.java" binary="false" 
+    corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="723" y="91"/>    
+    <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="8">    
+    <end type="SOURCE" refId="7" navigable="false">      
+      <attribute id="9" name="cars"/>      
+      <multiplicity id="10" minimum="0" maximum="2147483647"/>    
+    </end>    
+    <end type="TARGET" refId="3" navigable="true"/>    
+    <display labels="true" multiplicity="true"/>  
+  </association>  
+  <association id="11">    
+    <end type="SOURCE" refId="3" navigable="false">      
+      <attribute id="12" name="category"/>      
+      <multiplicity id="13" minimum="0" maximum="1"/>    
+    </end>    
+    <end type="TARGET" refId="6" 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>

collection-pipeline/pom.xml

@@ -1,4 +1,5 @@
-====
+<!--
+
     The MIT License
     Copyright (c) 2014 Ilkka Seppälä
 
@@ -19,5 +20,26 @@
     LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
     OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
     THE SOFTWARE.
-====
 
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>com.iluwatar</groupId>
+    <artifactId>java-design-patterns</artifactId>
+    <version>1.21.0-SNAPSHOT</version>
+  </parent>
+  <artifactId>collection-pipeline</artifactId>
+  <dependencies>
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-api</artifactId>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-engine</artifactId>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+</project>

collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/App.java

@@ -0,0 +1,76 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 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.collectionpipeline;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * In imperative-style programming, it is common to use for and while loops for
+ * most kinds of data processing. Function composition is a simple technique
+ * that lets you sequence modular functions to create more complex operations.
+ * When you run data through the sequence, you have a collection pipeline.
+ * Together, the Function Composition and Collection Pipeline patterns enable
+ * you to create sophisticated programs where data flow from upstream to
+ * downstream and is passed through a series of transformations.
+ *
+ */
+public class App {
+
+  private static final Logger LOGGER = LoggerFactory.getLogger(App.class);
+
+  /**
+   * Program entry point.
+   * 
+   * @param args
+   *            command line args
+   */
+  public static void main(String[] args) {
+
+    List<Car> cars = CarFactory.createCars();
+    
+    List<String> modelsImperative = ImperativeProgramming.getModelsAfter2000(cars);
+    LOGGER.info(modelsImperative.toString());
+
+    List<String> modelsFunctional = FunctionalProgramming.getModelsAfter2000(cars);
+    LOGGER.info(modelsFunctional.toString());
+    
+    Map<Category, List<Car>> groupingByCategoryImperative = ImperativeProgramming.getGroupingOfCarsByCategory(cars);
+    LOGGER.info(groupingByCategoryImperative.toString());
+
+    Map<Category, List<Car>> groupingByCategoryFunctional = FunctionalProgramming.getGroupingOfCarsByCategory(cars);
+    LOGGER.info(groupingByCategoryFunctional.toString());
+    
+    Person john = new Person(cars);
+    
+    List<Car> sedansOwnedImperative = ImperativeProgramming.getSedanCarsOwnedSortedByDate(Arrays.asList(john));
+    LOGGER.info(sedansOwnedImperative.toString());
+
+    List<Car> sedansOwnedFunctional = FunctionalProgramming.getSedanCarsOwnedSortedByDate(Arrays.asList(john));
+    LOGGER.info(sedansOwnedFunctional.toString());
+  }
+}

collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/Car.java

@@ -0,0 +1,109 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 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.collectionpipeline;
+
+/**
+ * A Car class that has the properties of make, model, year and category.
+ */
+public class Car {
+  private final String make;
+  private final String model;
+  private final int year;
+  private final Category category;
+
+  /**
+   * Constructor to create an instance of car.
+   * @param make the make of the car
+   * @param model the model of the car
+   * @param yearOfMake the year of built of the car
+   * @param category the {@link Category} of the car
+   */
+  public Car(String make, String model, int yearOfMake, Category category) {
+    this.make = make;
+    this.model = model;
+    this.year = yearOfMake;
+    this.category = category;
+  }
+
+  @Override
+  public int hashCode() {
+    final int prime = 31;
+    int result = 1;
+    result = prime * result + ((category == null) ? 0 : category.hashCode());
+    result = prime * result + ((make == null) ? 0 : make.hashCode());
+    result = prime * result + ((model == null) ? 0 : model.hashCode());
+    result = prime * result + year;
+    return result;
+  }
+
+  @Override
+  public boolean equals(Object obj) {
+    if (this == obj) {
+      return true;
+    }
+    if (obj == null) {
+      return false;
+    }
+    if (getClass() != obj.getClass()) {
+      return false;
+    }
+    Car other = (Car) obj;
+    if (category != other.category) {
+      return false;
+    }
+    if (make == null) {
+      if (other.make != null) {
+        return false;
+      }
+    } else if (!make.equals(other.make)) {
+      return false;
+    }
+    if (model == null) {
+      if (other.model != null) {
+        return false;
+      }
+    } else if (!model.equals(other.model)) {
+      return false;
+    }
+    if (year != other.year) {
+      return false;
+    }
+    return true;
+  }
+
+  public String getMake() {
+    return make;
+  }
+
+  public String getModel() {
+    return model;
+  }
+
+  public int getYear() {
+    return year;
+  }
+  
+  public Category getCategory() {
+    return category;
+  }
+}

collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/CarFactory.java

@@ -0,0 +1,47 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 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.collectionpipeline;
+
+import java.util.Arrays;
+import java.util.List;
+
+/**
+ * A factory class to create a collection of {@link Car} instances.
+ */
+public class CarFactory {
+  private CarFactory() {
+  }
+
+  /**
+   * Factory method to create a {@link List} of {@link Car} instances.
+   * @return {@link List} of {@link Car}
+   */
+  public static List<Car> createCars() {
+    return Arrays.asList(new Car("Jeep", "Wrangler", 2011, Category.JEEP),
+        new Car("Jeep", "Comanche", 1990, Category.JEEP),
+        new Car("Dodge", "Avenger", 2010, Category.SEDAN),
+        new Car("Buick", "Cascada", 2016, Category.CONVERTIBLE),
+        new Car("Ford", "Focus", 2012, Category.SEDAN),
+        new Car("Chevrolet", "Geo Metro", 1992, Category.CONVERTIBLE));
+  }
+}

collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/Category.java

@@ -0,0 +1,30 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 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.collectionpipeline;
+
+/**
+ * Enum for the category of car 
+ */
+public enum Category {
+  JEEP, SEDAN, CONVERTIBLE
+}

collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/FunctionalProgramming.java

@@ -0,0 +1,84 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 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.collectionpipeline;
+
+import java.util.Comparator;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+/**
+ * Iterating and sorting with a collection pipeline
+ * 
+ * <p>In functional programming, it's common to sequence complex operations through
+ * a series of smaller modular functions or operations. The series is called a
+ * composition of functions, or a function composition. When a collection of
+ * data flows through a function composition, it becomes a collection pipeline.
+ * Function Composition and Collection Pipeline are two design patterns
+ * frequently used in functional-style programming.
+ * 
+ * <p>Instead of passing a lambda expression to the map method, we passed the
+ * method reference Car::getModel. Likewise, instead of passing the lambda
+ * expression car -> car.getYear() to the comparing method, we passed the method
+ * reference Car::getYear. Method references are short, concise, and expressive.
+ * It is best to use them wherever possible.
+ * 
+ */
+public class FunctionalProgramming {
+  private FunctionalProgramming() {
+  }
+
+  /**
+   * Method to get models using for collection pipeline.
+   * 
+   * @param cars {@link List} of {@link Car} to be used for filtering
+   * @return {@link List} of {@link String} representing models built after year 2000
+   */
+  public static List<String> getModelsAfter2000(List<Car> cars) {
+    return cars.stream().filter(car -> car.getYear() > 2000)
+      .sorted(Comparator.comparing(Car::getYear))
+      .map(Car::getModel).collect(Collectors.toList());
+  }
+  
+  /**
+   * Method to group cars by category using groupingBy
+   * 
+   * @param cars {@link List} of {@link Car} to be used for grouping
+   * @return {@link Map} with category as key and cars belonging to that category as value
+   */
+  public static Map<Category, List<Car>> getGroupingOfCarsByCategory(List<Car> cars) {
+    return cars.stream().collect(Collectors.groupingBy(Car::getCategory));
+  }
+  
+  /**
+   * Method to get all Sedan cars belonging to a group of persons sorted by year of manufacture 
+   * 
+   * @param persons {@link List} of {@link Person} to be used
+   * @return {@link List} of {@link Car} to belonging to the group
+   */
+  public static List<Car> getSedanCarsOwnedSortedByDate(List<Person> persons) {
+    return persons.stream().map(Person::getCars).flatMap(List::stream)
+      .filter(car -> Category.SEDAN.equals(car.getCategory()))
+      .sorted(Comparator.comparing(Car::getYear)).collect(Collectors.toList());
+  }
+}

collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/ImperativeProgramming.java

@@ -0,0 +1,131 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 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.collectionpipeline;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * Imperative-style programming to iterate over the list and get the names of
+ * cars made later than the year 2000. We then sort the models in ascending
+ * order by year.
+ * 
+ * <p>As you can see, there's a lot of looping in this code. First, the
+ * getModelsAfter2000UsingFor method takes a list of cars as its parameter. It
+ * extracts or filters out cars made after the year 2000, putting them into a
+ * new list named carsSortedByYear. Next, it sorts that list in ascending order
+ * by year-of-make. Finally, it loops through the list carsSortedByYear to get
+ * the model names and returns them in a list.
+ * 
+ * <p>This short example demonstrates what I call the effect of statements. While
+ * functions and methods in general can be used as expressions, the {@link Collections}
+ * sort method doesn't return a result. Because it is used as a statement, it
+ * mutates the list given as argument. Both of the for loops also mutate lists
+ * as they iterate. Being statements, that's just how these elements work. As a
+ * result, the code contains unnecessary garbage variables
+ */
+public class ImperativeProgramming {
+  private ImperativeProgramming() {
+  }
+
+  /**
+   * Method to return the car models built after year 2000 using for loops.
+   * @param cars {@link List} of {@link Car} to iterate over
+   * @return {@link List} of {@link String} of car models built after year 2000
+   */
+  public static List<String> getModelsAfter2000(List<Car> cars) {
+    List<Car> carsSortedByYear = new ArrayList<>();
+
+    for (Car car : cars) {
+      if (car.getYear() > 2000) {
+        carsSortedByYear.add(car);
+      }
+    }
+
+    Collections.sort(carsSortedByYear, new Comparator<Car>() {
+      public int compare(Car car1, Car car2) {
+        return new Integer(car1.getYear()).compareTo(car2.getYear());
+      }
+    });
+
+    List<String> models = new ArrayList<>();
+    for (Car car : carsSortedByYear) {
+      models.add(car.getModel());
+    }
+
+    return models;
+  }
+  
+  /**
+   * Method to group cars by category using for loops
+   * 
+   * @param cars {@link List} of {@link Car} to be used for grouping
+   * @return {@link Map} with category as key and cars belonging to that category as value
+   */
+  public static Map<Category, List<Car>> getGroupingOfCarsByCategory(List<Car> cars) {
+    Map<Category, List<Car>> groupingByCategory = new HashMap<>();
+    for (Car car: cars) {
+      if (groupingByCategory.containsKey(car.getCategory())) {
+        groupingByCategory.get(car.getCategory()).add(car);
+      } else {
+        List<Car> categoryCars = new ArrayList<>();
+        categoryCars.add(car);
+        groupingByCategory.put(car.getCategory(), categoryCars);
+      }
+    }
+    return groupingByCategory;
+  }
+  
+  /**
+   * Method to get all Sedan cars belonging to a group of persons sorted by year of manufacture using for loops 
+   * 
+   * @param persons {@link List} of {@link Person} to be used
+   * @return {@link List} of {@link Car} to belonging to the group
+   */
+  public static List<Car> getSedanCarsOwnedSortedByDate(List<Person> persons) {
+    List<Car> cars = new ArrayList<>();
+    for (Person person: persons) {
+      cars.addAll(person.getCars());
+    }
+  
+    List<Car> sedanCars = new ArrayList<>();
+    for (Car car: cars) {
+      if (Category.SEDAN.equals(car.getCategory())) {
+        sedanCars.add(car);
+      }
+    }
+  
+    sedanCars.sort(new Comparator<Car>() {
+      @Override
+      public int compare(Car o1, Car o2) {
+        return o1.getYear() - o2.getYear();
+      }
+    });
+  
+    return sedanCars;
+  }
+}

collection-pipeline/src/main/java/com/iluwatar/collectionpipeline/Person.java

@@ -0,0 +1,44 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 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.collectionpipeline;
+
+import java.util.List;
+
+/**
+ * A Person class that has the list of cars that the person owns and use.
+ */
+public class Person {
+  private List<Car> cars;
+
+  /**
+   * Constructor to create an instance of person.
+   * @param cars the list of cars owned
+   */
+  public Person(List<Car> cars) {
+    this.cars = cars;
+  }
+
+  public List<Car> getCars() {
+    return cars;
+  }
+}

collection-pipeline/src/test/java/com/iluwatar/collectionpipeline/AppTest.java

@@ -0,0 +1,79 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 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.collectionpipeline;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Tests that Collection Pipeline methods work as expected.
+ */
+public class AppTest {
+  
+  private List<Car> cars = CarFactory.createCars();
+  
+  @Test
+  public void testGetModelsAfter2000UsingFor() {
+    List<String> models = ImperativeProgramming.getModelsAfter2000(cars);
+    assertEquals(Arrays.asList("Avenger", "Wrangler", "Focus", "Cascada"), models);
+  }
+  
+  @Test
+  public void testGetModelsAfter2000UsingPipeline() {
+    List<String> models = FunctionalProgramming.getModelsAfter2000(cars);
+    assertEquals(Arrays.asList("Avenger", "Wrangler", "Focus", "Cascada"), models);
+  }
+  
+  @Test
+  public void testGetGroupingOfCarsByCategory() {
+    Map<Category, List<Car>> modelsExpected = new HashMap<>();
+    modelsExpected.put(Category.CONVERTIBLE, Arrays.asList(new Car("Buick", "Cascada", 2016, Category.CONVERTIBLE),
+        new Car("Chevrolet", "Geo Metro", 1992, Category.CONVERTIBLE)));
+    modelsExpected.put(Category.SEDAN, Arrays.asList(new Car("Dodge", "Avenger", 2010, Category.SEDAN),
+        new Car("Ford", "Focus", 2012, Category.SEDAN)));
+    modelsExpected.put(Category.JEEP, Arrays.asList(new Car("Jeep", "Wrangler", 2011, Category.JEEP),
+        new Car("Jeep", "Comanche", 1990, Category.JEEP)));
+    Map<Category, List<Car>> modelsFunctional = FunctionalProgramming.getGroupingOfCarsByCategory(cars);
+    Map<Category, List<Car>> modelsImperative = ImperativeProgramming.getGroupingOfCarsByCategory(cars);
+    System.out.println("Category " + modelsFunctional);
+    assertEquals(modelsExpected, modelsFunctional);
+    assertEquals(modelsExpected, modelsImperative);
+  }
+  
+  @Test
+  public void testGetSedanCarsOwnedSortedByDate() {
+    Person john = new Person(cars);
+    List<Car> modelsExpected = Arrays.asList(new Car("Dodge", "Avenger", 2010, Category.SEDAN), 
+        new Car("Ford", "Focus", 2012, Category.SEDAN));
+    List<Car> modelsFunctional = FunctionalProgramming.getSedanCarsOwnedSortedByDate(Arrays.asList(john));
+    List<Car> modelsImperative = ImperativeProgramming.getSedanCarsOwnedSortedByDate(Arrays.asList(john));
+    assertEquals(modelsExpected, modelsFunctional);
+    assertEquals(modelsExpected, modelsImperative);
+  }
+}

command/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.19.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>command</artifactId>
   <dependencies>

composite/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.19.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>composite</artifactId>
   <dependencies>

converter/pom.xml

@@ -29,7 +29,7 @@
     <parent>
         <artifactId>java-design-patterns</artifactId>
         <groupId>com.iluwatar</groupId>
-        <version>1.19.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
     <modelVersion>4.0.0</modelVersion>
     <dependencies>

converter/src/main/java/com/iluwatar/converter/Converter.java

@@ -50,37 +50,37 @@ public class Converter<T, U> {
   }
 
   /**
-   * @param userDto DTO entity
+   * @param dto DTO entity
    * @return The domain representation - the result of the converting function application on dto entity.
    */
-  public final U convertFromDto(final T userDto) {
-    return fromDto.apply(userDto);
+  public final U convertFromDto(final T dto) {
+    return fromDto.apply(dto);
   }
 
   /**
-   * @param user domain entity
+   * @param entity domain entity
    * @return The DTO representation - the result of the converting function application on domain entity.
    */
-  public final T convertFromEntity(final U user) {
-    return fromEntity.apply(user);
+  public final T convertFromEntity(final U entity) {
+    return fromEntity.apply(entity);
   }
 
   /**
-   * @param dtoUsers collection of DTO entities
+   * @param dtos collection of DTO entities
    * @return List of domain representation of provided entities retrieved by
    *        mapping each of them with the conversion function
    */
-  public final List<U> createFromDtos(final Collection<T> dtoUsers) {
-    return dtoUsers.stream().map(this::convertFromDto).collect(Collectors.toList());
+  public final List<U> createFromDtos(final Collection<T> dtos) {
+    return dtos.stream().map(this::convertFromDto).collect(Collectors.toList());
   }
 
   /**
-   * @param users collection of domain entities
+   * @param entities collection of domain entities
    * @return List of domain representation of provided entities retrieved by
    *        mapping each of them with the conversion function
    */
-  public final List<T> createFromEntities(final Collection<U> users) {
-    return users.stream().map(this::convertFromEntity).collect(Collectors.toList());
+  public final List<T> createFromEntities(final Collection<U> entities) {
+    return entities.stream().map(this::convertFromEntity).collect(Collectors.toList());
   }
 
 }

converter/src/test/java/com/iluwatar/converter/ConverterTest.java

@@ -71,7 +71,7 @@ public class ConverterTest {
         user.getFirstName().toLowerCase() + user.getLastName().toLowerCase() + "@whatever.com"));
     User u1 = new User("John", "Doe", false, "12324");
     UserDto userDto = converter.convertFromEntity(u1);
-    assertEquals(userDto.getEmail(), "johndoe@whatever.com");
+    assertEquals("johndoe@whatever.com", userDto.getEmail());
   }
 
   /**
@@ -83,6 +83,6 @@ public class ConverterTest {
     ArrayList<User> users = Lists.newArrayList(new User("Camile", "Tough", false, "124sad"),
         new User("Marti", "Luther", true, "42309fd"), new User("Kate", "Smith", true, "if0243"));
     List<User> fromDtos = userConverter.createFromDtos(userConverter.createFromEntities(users));
-    assertEquals(fromDtos, users);
+    assertEquals(users, fromDtos);
   }
 }

cqrs/pom.xml

@@ -21,7 +21,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>java-design-patterns</artifactId>
-		<version>1.19.0</version>
+		<version>1.21.0-SNAPSHOT</version>
 	</parent>
 	<artifactId>cqrs</artifactId>
 	<dependencies>

cqrs/src/test/java/com/iluwatar/cqrs/IntegrationTest.java

@@ -96,7 +96,7 @@ public class IntegrationTest {
   @Test
   public void testGetAuthorBooks() {
     List<Book> books = queryService.getAuthorBooks("username1");
-    assertTrue(books.size() == 2);
+    assertEquals(2, books.size());
     assertTrue(books.contains(new Book("title1", 10)));
     assertTrue(books.contains(new Book("new_title2", 30)));
   }

dao/pom.xml

@@ -30,7 +30,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.19.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>dao</artifactId>
 

dao/src/test/java/com/iluwatar/dao/CustomerTest.java

@@ -88,13 +88,7 @@ public class CustomerTest {
 
   @Test
   public void testToString() {
-    final StringBuffer buffer = new StringBuffer();
-    buffer.append("Customer{id=")
-            .append("" + customer.getId())
-            .append(", firstName='")
-            .append(customer.getFirstName())
-            .append("\', lastName='")
-            .append(customer.getLastName() + "\'}");
-    assertEquals(buffer.toString(), customer.toString());
+    assertEquals(String.format("Customer{id=%s, firstName='%s', lastName='%s'}",
+        customer.getId(), customer.getFirstName(), customer.getLastName()), customer.toString());
   }
 }

dao/src/test/java/com/iluwatar/dao/DbCustomerDaoTest.java

@@ -257,7 +257,7 @@ public class DbCustomerDaoTest {
 
   private void assertCustomerCountIs(int count) throws Exception {
     try (Stream<Customer> allCustomers = dao.getAll()) {
-      assertTrue(allCustomers.count() == count);
+      assertEquals(count, allCustomers.count());
     }
   }
 

dao/src/test/java/com/iluwatar/dao/InMemoryCustomerDaoTest.java

@@ -156,7 +156,7 @@ public class InMemoryCustomerDaoTest {
   
   private void assertCustomerCountIs(int count) throws Exception {
     try (Stream<Customer> allCustomers = dao.getAll()) {
-      assertTrue(allCustomers.count() == count);
+      assertEquals(count, allCustomers.count());
     }
   }
 }

data-bus/pom.xml

@@ -33,7 +33,7 @@
     <parent>
         <groupId>com.iluwatar</groupId>
         <artifactId>java-design-patterns</artifactId>
-        <version>1.19.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
     <artifactId>data-bus</artifactId>
     <dependencies>

data-mapper/pom.xml

@@ -28,7 +28,7 @@
 	<parent>
 		<groupId>com.iluwatar</groupId>
 		<artifactId>java-design-patterns</artifactId>
-		<version>1.19.0</version>
+		<version>1.21.0-SNAPSHOT</version>
 	</parent>
 	<artifactId>data-mapper</artifactId>
 	<dependencies>

data-mapper/src/test/java/com/iluwatar/datamapper/DataMapperTest.java

@@ -21,6 +21,7 @@ package com.iluwatar.datamapper;
 import org.junit.jupiter.api.Test;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
 
 /**
  * The Data Mapper (DM) is a layer of software that separates the in-memory objects from the
@@ -43,27 +44,29 @@ public class DataMapperTest {
     final StudentDataMapper mapper = new StudentDataMapperImpl();
 
     /* Create new student */
-    Student student = new Student(1, "Adam", 'A');
+    int studentId = 1;
+    Student student = new Student(studentId, "Adam", 'A');
 
     /* Add student in respectibe db */
     mapper.insert(student);
 
     /* Check if student is added in db */
-    assertEquals(student.getStudentId(), mapper.find(student.getStudentId()).get().getStudentId());
+    assertEquals(studentId, mapper.find(student.getStudentId()).get().getStudentId());
 
     /* Update existing student object */
-    student = new Student(student.getStudentId(), "AdamUpdated", 'A');
+    String updatedName = "AdamUpdated";
+    student = new Student(student.getStudentId(), updatedName, 'A');
 
     /* Update student in respectibe db */
     mapper.update(student);
 
     /* Check if student is updated in db */
-    assertEquals(mapper.find(student.getStudentId()).get().getName(), "AdamUpdated");
+    assertEquals(updatedName, mapper.find(student.getStudentId()).get().getName());
 
     /* Delete student in db */
     mapper.delete(student);
 
     /* Result should be false */
-    assertEquals(false, mapper.find(student.getStudentId()).isPresent());
+    assertFalse(mapper.find(student.getStudentId()).isPresent());
   }
 }

data-mapper/src/test/java/com/iluwatar/datamapper/StudentTest.java

@@ -20,7 +20,9 @@ package com.iluwatar.datamapper;
 
 import org.junit.jupiter.api.Test;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotEquals;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 /**
@@ -28,28 +30,27 @@ import static org.junit.jupiter.api.Assertions.assertTrue;
  */
 public final class StudentTest {
 
-  @Test
   /**
    * This API tests the equality behaviour of Student object
    * Object Equality should work as per logic defined in equals method
    *
    * @throws Exception if any execution error during test
    */
+  @Test
   public void testEquality() throws Exception {
 
     /* Create some students */
     final Student firstStudent = new Student(1, "Adam", 'A');
     final Student secondStudent = new Student(2, "Donald", 'B');
     final Student secondSameStudent = new Student(2, "Donald", 'B');
-    final Student firstSameStudent = firstStudent;
 
     /* Check equals functionality: should return 'true' */
-    assertTrue(firstStudent.equals(firstSameStudent));
+    assertEquals(firstStudent, firstStudent);
 
     /* Check equals functionality: should return 'false' */
-    assertFalse(firstStudent.equals(secondStudent));
+    assertNotEquals(firstStudent, secondStudent);
 
     /* Check equals functionality: should return 'true' */
-    assertTrue(secondStudent.equals(secondSameStudent));
+    assertEquals(secondStudent, secondSameStudent);
   }
 }

data-transfer-object/pom.xml

@@ -28,7 +28,7 @@
     <parent>
         <groupId>com.iluwatar</groupId>
         <artifactId>java-design-patterns</artifactId>
-        <version>1.19.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
     <artifactId>data-transfer-object</artifactId>
     <dependencies>

data-transfer-object/src/test/java/com/iluwatar/datatransfer/CustomerResourceTest.java

@@ -30,6 +30,7 @@ import java.util.ArrayList;
 import java.util.List;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 /**
  * tests {@link CustomerResource}.
@@ -45,10 +46,10 @@ public class CustomerResourceTest {
 
     List<CustomerDto> allCustomers = customerResource.getAllCustomers();
 
-    assertEquals(allCustomers.size(), 1);
-    assertEquals(allCustomers.get(0).getId(), "1");
-    assertEquals(allCustomers.get(0).getFirstName(), "Melody");
-    assertEquals(allCustomers.get(0).getLastName(), "Yates");
+    assertEquals(1, allCustomers.size());
+    assertEquals("1", allCustomers.get(0).getId());
+    assertEquals("Melody", allCustomers.get(0).getFirstName());
+    assertEquals("Yates", allCustomers.get(0).getLastName());
   }
 
   @Test
@@ -59,9 +60,9 @@ public class CustomerResourceTest {
     customerResource.save(customer);
 
     List<CustomerDto> allCustomers = customerResource.getAllCustomers();
-    assertEquals(allCustomers.get(0).getId(), "1");
-    assertEquals(allCustomers.get(0).getFirstName(), "Rita");
-    assertEquals(allCustomers.get(0).getLastName(), "Reynolds");
+    assertEquals("1", allCustomers.get(0).getId());
+    assertEquals("Rita", allCustomers.get(0).getFirstName());
+    assertEquals("Reynolds", allCustomers.get(0).getLastName());
   }
 
   @Test
@@ -75,7 +76,7 @@ public class CustomerResourceTest {
     customerResource.delete(customer.getId());
 
     List<CustomerDto> allCustomers = customerResource.getAllCustomers();
-    assertEquals(allCustomers.size(), 0);
+    assertTrue(allCustomers.isEmpty());
   }
 
 }

decorator/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.19.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>decorator</artifactId>
   <dependencies>

delegation/pom.xml

@@ -30,7 +30,7 @@
     <parent>
         <artifactId>java-design-patterns</artifactId>
         <groupId>com.iluwatar</groupId>
-        <version>1.19.0</version>
+        <version>1.21.0-SNAPSHOT</version>
     </parent>
     <modelVersion>4.0.0</modelVersion>
 

delegation/src/main/java/com/iluwatar/delegation/simple/App.java

@@ -40,7 +40,7 @@ import com.iluwatar.delegation.simple.printers.HpPrinter;
  */
 public class App {
 
-  public static final String MESSAGE_TO_PRINT = "hello world";
+  private static final String MESSAGE_TO_PRINT = "hello world";
 
   /**
    * Program entry point

dependency-injection/pom.xml

@@ -29,7 +29,7 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.19.0</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
   <artifactId>dependency-injection</artifactId>
   <dependencies>

dirty-flag/README.md

@@ -0,0 +1,26 @@
+---
+layout: pattern
+title: Dirty Flag
+folder: dirty-flag
+permalink: /patterns/dirty-flag/
+categories: Other
+tags:
+ - Java
+ - Difficulty-Beginner
+ - Performance
+---
+
+## Intent
+To avoid expensive re-acquisition of resources. The resources retain their identity, are kept in some
+fast-access storage, and are re-used to avoid having to acquire them again.
+
+![alt text](./etc/dirty-flag.png "Dirty Flag")
+
+## Applicability
+Use the Dirty Flag pattern when
+
+* Repetitious acquisition, initialization, and release of the same resource causes unnecessary performance overhead.
+
+## Credits
+
+* [Design Patterns: Dirty Flag](https://www.takeupcode.com/podcast/89-design-patterns-dirty-flag/)

dirty-flag/etc/dirty-flag.ucls

@@ -0,0 +1,45 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<class-diagram version="1.2.2" icons="true" automaticImage="PNG" 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.dirtyflag.App" project="dirty-flag" 
+    file="/dirty-flag/src/main/java/com/iluwatar/dirtyflag/App.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="266" y="188"/>    
+    <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.dirtyflag.DataFetcher" project="dirty-flag" 
+    file="/dirty-flag/src/main/java/com/iluwatar/dirtyflag/DataFetcher.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="153" width="125" x="66" y="291"/>    
+    <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.dirtyflag.World" project="dirty-flag" 
+    file="/dirty-flag/src/main/java/com/iluwatar/dirtyflag/World.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="379" y="366"/>    
+    <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="3" navigable="false">      
+      <attribute id="5" name="df"/>      
+      <multiplicity id="6" minimum="0" maximum="1"/>    
+    </end>    
+    <end type="TARGET" refId="2" 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>

dirty-flag/pom.xml

@@ -2,7 +2,7 @@
 <!--
 
     The MIT License
-    Copyright (c) 2014-2016 Ilkka Seppälä
+    Copyright (c) 2014 Ilkka Seppälä
 
     Permission is hereby granted, free of charge, to any person obtaining a copy
     of this software and associated documentation files (the "Software"), to deal
@@ -29,21 +29,25 @@
   <parent>
     <groupId>com.iluwatar</groupId>
     <artifactId>java-design-patterns</artifactId>
-    <version>1.0-SNAPSHOT</version>
+    <version>1.21.0-SNAPSHOT</version>
   </parent>
-  <artifactId>dao</artifactId>
+  <groupId>com.iluwatar</groupId>
+  <artifactId>dirty-flag</artifactId>
+  <version>1.21.0-SNAPSHOT</version>
+  <name>dirty-flag</name>
+  <url>http://maven.apache.org</url>
+  <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+  </properties>
   <dependencies>
 	<dependency>
-	    <groupId>org.hibernate</groupId>
-	    <artifactId>hibernate-core</artifactId>
-	</dependency>
-	<dependency>
-		<groupId>com.h2database</groupId>
-		<artifactId>h2</artifactId>
-	</dependency>  
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-api</artifactId>
+      <scope>test</scope>
+    </dependency>
     <dependency>
-      <groupId>junit</groupId>
-      <artifactId>junit</artifactId>
+      <groupId>org.junit.jupiter</groupId>
+      <artifactId>junit-jupiter-engine</artifactId>
       <scope>test</scope>
     </dependency>
   </dependencies>

dirty-flag/src/main/java/com/iluwatar/dirtyflag/App.java

@@ -0,0 +1,82 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014-2016 Ilkka Seppälä
+ * <p>
+ * 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:
+ * <p>
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ * <p>
+ * 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.dirtyflag;
+
+import java.util.List;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.TimeUnit;
+
+/**
+ *
+ * This application demonstrates the <b>Dirty Flag</b> pattern. The dirty flag behavioral pattern allows you to avoid
+ * expensive operations that would just need to be done again anyway. This is a simple pattern that really just explains
+ * how to add a bool value to your class that you can set anytime a property changes. This will let your class know that
+ * any results it may have previously calculated will need to be calculated again when they’re requested. Once the
+ * results are re-calculated, then the bool value can be cleared.
+ * 
+ * There are some points that need to be considered before diving into using this pattern:- there are some things you’ll
+ * need to consider:- (1) Do you need it? This design pattern works well when the results to be calculated are difficult
+ * or resource intensive to compute. You want to save them. You also don’t want to be calculating them several times in
+ * a row when only the last one counts. (2) When do you set the dirty flag? Make sure that you set the dirty flag within
+ * the class itself whenever an important property changes. This property should affect the result of the calculated
+ * result and by changing the property, that makes the last result invalid. (3) When do you clear the dirty flag? It
+ * might seem obvious that the dirty flag should be cleared whenever the result is calculated with up-to-date
+ * information but there are other times when you might want to clear the flag.
+ *
+ * In this example, the {@link DataFetcher} holds the <i>dirty flag</i>. It fetches and re-fetches from <i>world.txt</i>
+ * when needed. {@link World} mainly serves the data to the front-end.
+ */
+public class App {
+  /**
+   * Program execution point
+   */
+  public void run() {
+
+    final ScheduledExecutorService executorService = Executors.newSingleThreadScheduledExecutor();
+    executorService.scheduleAtFixedRate(new Runnable() {
+      @Override
+      public void run() {
+        World world = new World();
+        List<String> countries = world.fetch();
+        System.out.println("Our world currently has the following countries:-");
+        for (String country : countries) {
+          System.out.println("\t" + country);
+        }
+      }
+    }, 0, 15, TimeUnit.SECONDS); // Run at every 15 seconds.
+  }
+
+  /**
+   * Program entry point
+   *
+   * @param args
+   *          command line args
+   */
+  public static void main(String[] args) {
+    App app = new App();
+
+    app.run();
+  }
+
+}

dirty-flag/src/main/java/com/iluwatar/dirtyflag/DataFetcher.java

@@ -0,0 +1,81 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 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.dirtyflag;
+
+import java.io.BufferedReader;
+import java.io.File;
+import java.io.FileReader;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * A mock database manager -- Fetches data from a raw file.
+ * 
+ * @author swaisuan
+ *
+ */
+public class DataFetcher {
+
+  private final String filename = "world.txt";
+  private long lastFetched;
+
+  public DataFetcher() {
+    this.lastFetched = -1;
+  }
+
+  private boolean isDirty(long fileLastModified) {
+    if (lastFetched != fileLastModified) {
+      lastFetched = fileLastModified;
+      return true;
+    }
+    return false;
+  }
+
+  /**
+   * Fetches data/content from raw file.
+   * 
+   * @return List of strings
+   */
+  public List<String> fetch() {
+    ClassLoader classLoader = getClass().getClassLoader();
+    File file = new File(classLoader.getResource(filename).getFile());
+
+    if (isDirty(file.lastModified())) {
+      System.out.println(filename + " is dirty! Re-fetching file content...");
+
+      List<String> data = new ArrayList<String>();
+      try (BufferedReader br = new BufferedReader(new FileReader(file))) {
+        String line;
+        while ((line = br.readLine()) != null) {
+          data.add(line);
+        }
+      } catch (IOException e) {
+        e.printStackTrace();
+      }
+      return data;
+    }
+
+    return new ArrayList<String>();
+  }
+}

dirty-flag/src/main/java/com/iluwatar/dirtyflag/World.java

@@ -0,0 +1,58 @@
+/**
+ * The MIT License
+ * Copyright (c) 2014 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.dirtyflag;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * 
+ * A middle-layer app that calls/passes along data from the back-end.
+ * 
+ * @author swaisuan
+ *
+ */
+public class World {
+
+  private List<String> countries;
+  private DataFetcher df;
+
+  public World() {
+    this.countries = new ArrayList<String>();
+    this.df = new DataFetcher();
+  }
+
+  /**
+   * 
+   * Calls {@link DataFetcher} to fetch data from back-end.
+   * 
+   * @return List of strings
+   */
+  public List<String> fetch() {
+    List<String> data = df.fetch();
+
+    countries = data.isEmpty() ? countries : data;
+
+    return countries;
+  }
+}

dirty-flag/src/main/resources/world.txt

@@ -21,3 +21,6 @@
     THE SOFTWARE.
 ====
 
+UNITED_KINGDOM
+MALAYSIA
+UNITED_STATES