编程模式之观察者模式(Observer)

package com.observer;

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

/**
 * 抽象主题角色，被观察
 * @author hyp
 *
 */
public interface Subject
{
    void addWatcher(Watcher watcher);
    void removeWatcher(Watcher watcher);
    void notify(String message);
}


/**
 * 抽象观察者角色，观察主题
 * @author hyp
 *
 */
public interface Watcher
{
    void update(String message);
}




/**
 * 具体主题角色
 * @author hyp
 *
 */
public class ConcreteSubject implements Subject
{
    private List<Watcher> watchers = new ArrayList<Watcher>();
    
    @Override
    public void addWatcher(Watcher watcher)
    {
        watchers.add(watcher);
    }

    @Override
    public void removeWatcher(Watcher watcher)
    {
        watchers.remove(watcher);
    }

    @Override
    public void notify(String message)
    {
        for(Watcher w:watchers)
        {
            w.update(message);
        }
    }
}


/**
 * 具体观察者橘色
 * @author hyp
 *
 */
public class ConcreteWatcher implements Watcher
{

    @Override
    public void update(String message)
    {
        System.out.println(this.toString()+ ":" + message);
    }
}

/**
 * 测试观察者模式
 * @author hyp
 *
 */
public class Test
{
    public static void main(String[] args)
    {
        Subject subject= new ConcreteSubject();
        Watcher watcher1 = new ConcreteWatcher();
        Watcher watcher2 = new ConcreteWatcher();
        Watcher watcher3 = new ConcreteWatcher();
        
        Subject.addWatcher(watcher1);//添加观察者
        Subject.addWatcher(watcher2);
        Subject.addWatcher(watcher3);
        
        Subject.notify("Hello");//通知所有观察者
        
        Subject.removeWatcher(watcher1);//移除一个观察者
        
        Subject.notify("bye~");
        
    }
}