这方面的资料搜索一下很多,但是自己一直没有实践过。今天用到了,做下记录。名词解释:

观察者,Observer
被观察者,Observable

举例,过年放烟花,烟花放在中间一直燃烧,就是被观察者;
而大家在周围看,就是观察者(哇~猴赛雷)
直接上代码:

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/**
* 作为被观察者也作为被订阅源
*
* @author Administrator
*
*/
static class Fireworks extends Observable {

void setFire() {
System.out.println("I am fired, check on that");

//事件變化,通知所有觀察者
super.setChanged();
this.notifyObservers("qiu...qiu...qiu...");
}
}

/**
* 觀察者
*
* @author Administrator
*
*/
static class People implements Observer {

String name = "";

public People(String name) {
this.name = name;
}

public void update(Observable o, Object arg) {
System.out.println(name + " watched: " + arg);
}
}

测试一下:

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Fireworks f = new Fireworks();

// 注冊觀察者
f.addObserver(new People("XiaoMing"));
f.addObserver(new People("XiaoQiang"));
f.addObserver(new People("XiaoHong"));
f.addObserver(new People("XiaoLi"));

f.setFire();

输出:

I am fired, check on that
XiaoLi watched: qiu…qiu…qiu…
XiaoHong watched: qiu…qiu…qiu…
XiaoQiang watched: qiu…qiu…qiu…
XiaoMing watched: qiu…qiu…qiu…

之前使用的是直接new一个Observable对象,导致无法调用父类的setChanged方法。

见->java 订阅者模式不执行update