implements Twin design pattern #63

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

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+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

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+
+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

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+
+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

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+
+
+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

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