简介：
在java.util包下，
观察者继承observable类，设置变化点setChanged();通知改变的内容notifyObservers();
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;
}
@Override
public 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 stub
House 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
