观察者模式

观察者模式的思想是有一个目标对象，这个对象发生了变化时，所以关心他变化的对象都会被通知到。下面是个典型的消息通信的例子：

package com.jerry.design.observer;

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


	// 测试类
public class Test {

	public static void main(String[] args) {
		//消息提供者
		Message m = new Message();
		//消息消费者
		Consumer c1 = new Consumer("c1");
		Consumer c2 = new Consumer("c2");
		Consumer c3 = new Consumer("c3");
		//注册消费者
		m.attach(c1);
		m.attach(c2);
		m.attach(c3);
		
		//生产消息
		m.setContent("我生产消息了！");
	}
}
interface Oberver{
	 public void update(Subject subject);
}

class Consumer implements Oberver{

	private String name;
	
	@Override
	public void update(Subject subject) {
		System.out.println("消息："+((Message)subject).getContent()+"被"+name+"消费了");
		
	}

	public Consumer(String name) {
		super();
		this.name = name;
	}
	
}
class Subject{
	
	private List<Oberver> consumers = new ArrayList<Oberver>();
	
	public void attach(Oberver consumer){
		consumers.add(consumer);
	}
	
	public void detach(Oberver consumer){
		consumers.remove(consumer);
	}
	
	protected void notifyObervers(){
		for(Oberver oberver:consumers){
			oberver.update(this);
		}
	}
	
}

class Message extends Subject{
	
	private String content;

	public String getContent() {
		return content;
	}

	public void setContent(String content) {
		this.content = content;
		notifyObervers();
	}
	
	
}