Java自带的观察者模式及实现方法详解

package com.test.observer;
import java.util.Observable;
public class ServerManager extends Observable {
private int data = 0;
public int getData(){ return data; }
public void setData(int i){
if(this.data != i){ this.data = i;setChanged();}
notifyObservers(); //只有在setChange()被调用后，notifyObservers()才会去调用update()，否则什么都不干。 } }
}
}

import java.util.Observable;
import java.util.Observer;
public class AObserver implements Observer {

public AObserver(ServerManager sm) {
super();
// TODO Auto-generated constructor stub
sm.addObserver(this);　　//注册加入观察者
}
@Override
public void update(Observable arg0, Object arg1) {
System.out.println("AObserver receive:Data has changed to "+((ServerManager) arg0).getData());
}
}

import java.util.Observable;
import java.util.Observer;
public class BObserver implements Observer {

public BObserver(ServerManager sm) {
super();
sm.addObserver(this);　　//注册加入观察者
}
@Override
public void update(Observable o, Object arg) {
// TODO Auto-generated method stub
System.out.println("BObserver receive:Data has changed to "+((ServerManager) o).getData());
}
}

public class TestDemo {
public static void main(String[] args) {
// TODO Auto-generated method stub
ServerManager sm = new ServerManager();
AObserver a = new AObserver(sm);
BObserver b = new BObserver(sm);
sm.setData(5);
sm.deleteObserver(a);　　//注销观察者，以后被观察者有数据变化就不再通知这个已注销的观察者
sm.setData(10);
}
}