简介：

在java.util包下，

1. 观察者继承observable类，设置变化点setChanged();通知改变的内容notifyObservers();

2. 被观察者继承observer接口，覆写uodate方法

要点：Observer中的update方法中的变量含义

• 代码：被观察者房子House类

package observer_java;
import java.util.Observable;
/*** 被观察者需要继承Observable类* @author LCM**/
public class House extends Observable{private String houseName;public String getHouseName() {return houseName;}public House(String houseName, double price) {super();this.houseName = houseName;this.price = price;}public House() {super();}public void setHouseName(String houseName) {this.houseName = houseName;}private double price;public double getPrice() {return price;}public void setPrice(double price) {this.setChanged();//设置变化点this.notifyObservers(price);//通知所有观察者改变价格this.price = price;}@Overridepublic String toString(){return this.getHouseName()+"的价格是："+this.getPrice();}
}

• 代码二：观察者购房者HouseObserve

package observer_java;
import java.util.Observable;
import java.util.Observer;
/*** 观察者需要集成接口observer* @author LCM**/
public class HouseObserver implements Observer{private String name;public HouseObserver() {super();}public HouseObserver(String name) {super();this.name = name;}public String getName() {return name;}public void setName(String name) {this.name = name;}
/**覆写update方法，实现观察者的方式
*update(Obervable o,Object arg)中的o是原来的对象，还未改变的，arg是改**变的变量
*/public void update(Observable o, Object arg) {// TODO Auto-generated method stubHouse h=(House)o;System.out.println("房子原来的价格是"+h.getPrice());System.out.println(this.getName()+"发现房子价格变化："+arg);}public static void main(String args[]){House newHouse=new House("Bluse Lee",3000);HouseObserver observer1=new HouseObserver("observer1");HouseObserver observer2=new HouseObserver("observer2");HouseObserver observer3=new HouseObserver("observer3");newHouse.addObserver(observer1);newHouse.addObserver(observer2);newHouse.addObserver(observer3);System.out.println(newHouse);newHouse.setPrice(5000);System.out.println(newHouse);}
}
//Bluse Lee的价格是：3000.0
//observer3发现房子价格变化：Bluse Lee的价格是：3000.0
//observer2发现房子价格变化：Bluse Lee的价格是：3000.0
//observer1发现房子价格变化：Bluse Lee的价格是：3000.0
//Bluse Lee的价格是：5000.0
//错误分析：update(Obervable o,Object arg)中的o是原来的对象，还未改变的，arg是改变的变量