观察者模式

[关键字]:java,design pattern,设计模式,《Java与模式》学习,阎宏,Ph.D,Factory,观察者模式,observer,event,java自定义事件,java事件机制,事件模型,事件监听,订阅发布,事件消息 

[环境]:StarUML5.0 + JDK6 

[正文]:

package pattern.observer; 

import java.util.Observer; 

import java.util.Observable;

/** 

* 观察者(Observer)模式: 

* 使用Java类库支持的观察者模式 

* java.util.Observer 

* java.util.Observable

运行结果: 

Prievious:,Changed:abc 

Prievious:abc,Changed:abcd 

Prievious:abcd,Changed:f

* @version 2009-5-6 

* @author Winty([email protected]) 

*/ 

public class ObserverTest{ 

    public static void main(String[] args){ 

        Watched watched = new Watched(); 

        Watcher watcher = new Watcher(); 

        watched.addObserver(watcher);

        watched.changeData("abc"); 

        watched.changeData("abcd"); 

        watched.changeData("f"); 

        watched.changeData(null); 

    } 

}

*具体被观察者,Observable是抽象被观察者 

class Watched extends Observable{ 

    private String data; 

    public Watched(){ 

        data = ""; 

    }

    public String retrieveData(){ 

        return data; 

    public void changeData(String data){ 

        if(data!=null && !this.data.equals(data)){ 

            String dt = this.data;//记录变化前的数据 

            this.data = data;

            setChanged(); 

            notifyObservers(dt); 

        }        

*具体观察者,抽象观察者为Observer 

class Watcher implements Observer{ 

    @Override 

    public void update(Observable o , Object arg){ 

        Watched wathed = (Watched)o; 

        String previousData = (String)arg;

        System.out.print("Prievious:" + previousData + ","); 

        System.out.println("Changed:" + wathed.retrieveData()); 

[附件]:

pattern_Observable.zip

本文转自wintys 51CTO博客，原文链接:http://blog.51cto.com/wintys/211257