//抽象主題角色，watched：被觀察
public interface Watched
{
    public void addWatcher(Watcher watcher);

    public void removeWatcher(Watcher watcher);

    public void notifyWatchers(Watcher watcher,String str);

}

//抽象觀察者角色
public interface Watcher
{
    public void update(String str);

}

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

/**觀察者管理
 * @author huangziwang
 *
 */
public class ConcreteWatched implements Watched
{
    // 存放觀察者
    private static List<Watcher> list = new ArrayList<Watcher>();

    public void addWatcher(Watcher watcher)
    {
        list.add(watcher);
    }

    public void removeWatcher(Watcher watcher)
    {
        list.remove(watcher);
    }

    public void notifyWatchers(Watcher watcher1,String str)
    {
        // 自動呼叫實際上是主題進行呼叫的
    	Iterator<Watcher> e = list.iterator();
    	while (e.hasNext()) {
    		Watcher watcher = e.next();
 

                //精確找出觀察者返回函式並從佇列中刪除
    		if (watcher.equals(watcher1)) {
        		watcher.update(str);
        		e.remove();
        		System.out.println(list.size());
    		}
		}
    }

}

public class ConcreteWatcher implements Watcher
{

    public void update(String str)
    {
        System.out.println(str);
    }

}
 

public class TestThread extends Thread {
	private Watcher watcher;
	// 將被觀察者物件傳入執行緒，這裡充分顯示了面向物件開發的好處
	public TestThread (Watcher watcher) {
		this.watcher = watcher;
	}
	public void run() {
		Watched concreteWatched = new ConcreteWatched();
		concreteWatched.notifyWatchers(watcher, "我是:" + hashCode());
	}

}
 

public class Test
{
    public static void main(String[] args)
    {
        Watched girl = new ConcreteWatched();
        // 將觀察者加入佇列中
        Watcher watcher1 = new ConcreteWatcher();
        girl.addWatcher(watcher1);
        TestThread t = new TestThread(watcher1);
        t.start();
    }
}

丟擲結果

我是:743319257
0