设计模式 观察者

import java.util.HashSet;
public class ObserverPattern {
public static void main(String[] args) {
Product p = new Product("《java编程思想》",100.00);
Observer o1 = new WebObserver();
Observer o2 = new MailObserver();
p.addObserver(o1);
p.addObserver(o2);
System.out.println("第一次价格变动");
p.setPrice(80);
// o1.unreg(p);
System.out.println("第二次价格变动");
p.setPrice(150);
}
}
interface Observer{
public void update(Product p);
public void unreg(Product p);
}
class WebObserver implements Observer{
public void update(Product p) {
System.out.println("更新页面价格："+p.getName()+":"+p.getPrice());
}
public void unreg(Product p) {
p.getObservers().remove(this);
}
}
class MailObserver implements Observer{
public void update(Product p) {
System.out.println("发送价格变化信息:"+p.getName()+":"+p.getPrice());
}
public void unreg(Product p) {
p.getObservers().remove(this);
}
}
class Product{
private double price;
private String name;
private HashSet<Observer> observers;
public Product (String name ,double price){
this.price=price;
this.name=name;
observers = new HashSet<Observer>();
}

public void addObserver(Observer ob) {
observers.add(ob);
}
public void notifyObserver() {
for (Observer ob : observers) {
ob.update(this);
}
}
public double getPrice(){
return price;
}
public void setPrice(double price) {
this.price=price;
notifyObserver();//价格变化时通知观察者
}
public String getName() {
return name;
}
public void setName(String name) {
this.name=name;
}
public HashSet<Observer> getObservers() {
return observers;
}
public void setObservers(HashSet<Observer> observers) {
this.observers=observers;
}
}