Design Pattern—— Observer Pattern 观察者模式

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Observer Pattern 观察者模式：

一.定义：

观察者模式定义了一种一对多的依赖关系，让多个观察者对象同时监听某一个主题对象。这个主题对象在状态上发生变化时，会通知所有的观察者对象，让他们能够自动更新自己：

二.组成：

1.抽象主题角色：（也就是被观察者的抽象）

package com.designPattern.observer;public interface watched {public void addWatcher(Watcher watcher);public void removeWatcher(Watcher watcher);public void notifyAllWatcher();}

2.抽象观察者角色：（也就是观察者的抽象）

package com.designPattern.observer;public interface Watcher {public void update();
}

3.具体主题角色：（也就是具体被观察者对象）

package com.designPattern.observer;import java.util.ArrayList;
import java.util.List;public class ConcreteWatched implements watched {private List<Watcher> list = new ArrayList<Watcher>();@Overridepublic void addWatcher(Watcher watcher) {list.add(watcher);}@Overridepublic void removeWatcher(Watcher watcher) {list.remove(watcher);}@Overridepublic void notifyAllWatcher() {for (Watcher watch : list) {watch.update();}}
}

4.具体观察者角色：

package com.designPattern.observer;public class ConcreteWatcher implements Watcher {private String id;public ConcreteWatcher(String id) {this.id = id;}@Overridepublic void update() {System.out.println("i am happy! " + this.id);}
}

ok 以上是这个观察者模式的4个主要组成。下面main调用：

package com.designPattern.observer;public class Client {public static void main(String[] args) {// 创建一个被观察者ConcreteWatched watched = new ConcreteWatched();// 创建4个观察者ConcreteWatcher watcher1 = new ConcreteWatcher("zhaan");ConcreteWatcher watcher2 = new ConcreteWatcher("lisi");ConcreteWatcher watcher3 = new ConcreteWatcher("xiaopin");// 把watcher1 到watcher3 这四个观察者注册到一个共同的主题watched上watched.addWatcher(watcher1);watched.addWatcher(watcher2);watched.addWatcher(watcher3);// 类似于addActionListener()函数把实现 ActionListener接口的类的对象注册到了button上。watched.addWatcher(new Watcher() {@Override
//类似于actionPerformed()函数
public void update() {System.out.println("i am happy!ooooooppppp ");}});watched.addWatcher(new ConcreteWatcher("hehe"));watched.notifyAllWatcher(); // 调用被观察者的notifyAllWatcher()函数，实际为遍历了所有依赖于该观察者的角色}}

输出结果：

i am happy! zhaan
i am happy! lisi
i am happy! xiaopin
i am happy!ooooooppppp
i am happy! hehe