implements Twin design pattern #63

pom.xml

@@ -68,6 +68,7 @@
 		<module>multiton</module>
 		<module>resource-acquisition-is-initialization</module>
 		<module>thread-pool</module>
+		<module>twin</module>
 		<module>private-class-data</module>
 		<module>object-pool</module>
 		<module>dependency-injection</module>

twin/.gitignore

@@ -0,0 +1 @@
+/target/

twin/etc/twin.ucls

@@ -0,0 +1,79 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<class-diagram version="1.1.8" icons="true" automaticImage="PNG" always-add-relationships="false" generalizations="true" 
+  realizations="true" associations="true" dependencies="false" nesting-relationships="true">  
+  <class id="1" language="java" name="com.iluwatar.twin.BallThread" project="twin" 
+    file="/twin/src/main/java/com/iluwatar/twin/BallThread.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="550" y="316"/>    
+    <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.twin.BallItem" project="twin" 
+    file="/twin/src/main/java/com/iluwatar/twin/BallItem.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="285" y="315"/>    
+    <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.twin.GameItem" project="twin" 
+    file="/twin/src/main/java/com/iluwatar/twin/GameItem.java" binary="false" corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="285" y="84"/>    
+    <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="java.lang.Thread" project="twin" 
+    file="/Library/Java/JavaVirtualMachines/jdk1.8.0_65.jdk/Contents/Home/jre/lib/rt.jar" binary="true" 
+    corner="BOTTOM_RIGHT">    
+    <position height="-1" width="-1" x="550" y="96"/>    
+    <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
+      sort-features="false" accessors="true" visibility="true">      
+      <attributes public="false" package="false" protected="false" private="false" static="true"/>      
+      <operations public="false" package="false" protected="false" private="false" static="true"/>    
+    </display>  
+  </class>  
+  <generalization id="5">    
+    <end type="SOURCE" refId="2"/>    
+    <end type="TARGET" refId="3"/>  
+  </generalization>  
+  <association id="6">    
+    <end type="SOURCE" refId="2" navigable="false">      
+      <attribute id="7" name="twin"/>      
+      <multiplicity id="8" minimum="0" maximum="1"/>    
+    </end>    
+    <end type="TARGET" refId="1" navigable="true"/>    
+    <display labels="true" multiplicity="true"/>  
+  </association>  
+  <association id="9">    
+    <end type="SOURCE" refId="4" navigable="false">      
+      <attribute id="10" name="threadQ"/>      
+      <multiplicity id="11" minimum="0" maximum="1"/>    
+    </end>    
+    <end type="TARGET" refId="4" navigable="true"/>    
+    <display labels="true" multiplicity="true"/>  
+  </association>  
+  <association id="12">    
+    <end type="SOURCE" refId="1" navigable="false">      
+      <attribute id="13" name="twin"/>      
+      <multiplicity id="14" minimum="0" maximum="1"/>    
+    </end>    
+    <end type="TARGET" refId="2" navigable="true"/>    
+    <display labels="true" multiplicity="true"/>  
+  </association>  
+  <generalization id="15">    
+    <end type="SOURCE" refId="1"/>    
+    <end type="TARGET" refId="4"/>  
+  </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>

twin/index.md

@@ -0,0 +1,20 @@
+---
+layout: pattern
+title: Twin
+folder: twin
+permalink: /patterns/twin/
+categories: Creational
+tags: Java
+---
+
+**Intent:**  Twin pattern is a design pattern which provides a standard solution to simulate multiple
+inheritance in java
+
+
+
+![alt text](./etc/twin.png "Twin")
+
+**Applicability:** Use the Twin idiom when
+
+* to simulate multiple inheritance in a language that does not support this feature.
+* to avoid certain problems of multiple inheritance such as name clashes.

twin/pom.xml

@@ -0,0 +1,18 @@
+<?xml version="1.0"?>
+<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>com.iluwatar</groupId>
+    <artifactId>java-design-patterns</artifactId>
+    <version>1.8.0-SNAPSHOT</version>
+  </parent>
+  <artifactId>twin</artifactId>
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+</project>

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

@@ -0,0 +1,53 @@
+package com.iluwatar.twin;
+
+/**
+ * Twin pattern is a design pattern which provides a standard solution to simulate multiple
+ * inheritance in java.
+ * 
+ * <p>
+ * In this example, there is a ball game, a ball needs to subclass {@link GameItem} which provide
+ * some common method like draw and click. Moreover, it needs to subclass {@link Thread} as ball is
+ * a moving item (we use {@link Thread} instead of implements {@link Runnable} for example only)
+ * <p>
+ * Threre is scenario, when user click the ball, the ball will stop, when user click it gain, it
+ * will resume to move. We create two class, ons is {@link BallItem} which subclass {@link GameItem}
+ * , another is {@link BallThread} which subclass {@link Thread}. These two object both hold a field
+ * named "Twin" reference to another object. In {@link BallItem#click()}, it will invoke
+ * {@link BallThread} to suspend or resume moving; in {@link BallThread#run()}, it will invoke
+ * {@link BallItem} for drawing.
+ * 
+ */
+public class App {
+
+  /**
+   * Program entry point
+   * 
+   * @param args command line args
+   */
+  public static void main(String[] args) throws Exception {
+
+    BallItem ballItem = new BallItem();
+    BallThread ballThread = new BallThread();
+
+    ballItem.setTwin(ballThread);
+    ballThread.setTwin(ballItem);
+
+    ballThread.start();
+
+    waiting();
+
+    ballItem.click();
+
+    waiting();
+
+    ballItem.click();
+
+    waiting();
+
+    ballThread.stopMe();
+  }
+
+  private static void waiting() throws Exception {
+    Thread.sleep(2500);
+  }
+}

twin/src/main/java/com/iluwatar/twin/BallItem.java

@@ -0,0 +1,41 @@
+
+package com.iluwatar.twin;
+
+/**
+ * This class represents a Ball which extends {@link GameItem} and implements the logic for ball
+ * item, like move and draw. It hold a reference of {@link BallThread} to delegate the suspend and
+ * resume task.
+ */
+public class BallItem extends GameItem {
+
+  private boolean isSuspended = false;
+
+  private BallThread twin;
+
+  public void setTwin(BallThread twin) {
+    this.twin = twin;
+  }
+
+  @Override
+  public void doDraw() {
+
+    System.out.println("doDraw");
+  }
+
+  public void move() {
+    System.out.println("move");
+  }
+
+  @Override
+  public void click() {
+
+    isSuspended = !isSuspended;
+
+    if (isSuspended) {
+      twin.suspendMe();
+    } else {
+      twin.resumeMe();
+    }
+  }
+}
+

twin/src/main/java/com/iluwatar/twin/BallThread.java

@@ -0,0 +1,53 @@
+
+package com.iluwatar.twin;
+
+/**
+ * This class is a UI thread for drawing the {@link BallItem}, and provide the method for suspend
+ * and resume. It hold the reference of {@link BallItem} to delegate the draw task.
+ * 
+ */
+
+public class BallThread extends Thread {
+
+  private BallItem twin;
+
+  private volatile boolean isSuspended;
+
+  private volatile boolean isRunning = true;
+
+  public void setTwin(BallItem twin) {
+    this.twin = twin;
+  }
+
+  public void run() {
+
+    while (isRunning) {
+      while (!isSuspended) {
+        twin.draw();
+        twin.move();
+        try {
+          Thread.sleep(1000);
+        } catch (InterruptedException e) {
+          throw new RuntimeException(e);
+        }
+
+      }
+    }
+  }
+
+  public void suspendMe() {
+    isSuspended = true;
+    System.out.println("Begin to suspend BallThread");
+  }
+
+  public void resumeMe() {
+    isSuspended = false;
+    System.out.println("Begin to resume BallThread");
+  }
+
+  public void stopMe() {
+    this.isRunning = false;
+    this.isSuspended = true;
+  }
+}
+

twin/src/main/java/com/iluwatar/twin/GameItem.java

@@ -0,0 +1,25 @@
+
+
+package com.iluwatar.twin;
+
+/**
+ * GameItem is a common class which provides some common methods for game object.
+ */
+public abstract class GameItem {
+
+  /**
+   * Template method, do some common logic before draw
+   * 
+   * @param other
+   * @return
+   */
+  public void draw() {
+    System.out.println("draw");
+    doDraw();
+  }
+
+  public abstract void doDraw();
+
+
+  public abstract void click();
+}

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

@@ -0,0 +1,17 @@
+package com.iluwatar.twin;
+
+import org.junit.Test;
+
+/**
+ * 
+ * Application test
+ *
+ */
+public class AppTest {
+
+  @Test
+  public void test() throws Exception {
+    String[] args = {};
+    App.main(args);
+  }
+}