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(); } }