1. 定义
观察者模式很好理解,类似于邮件订阅和RSS订阅,当我们浏览一些博客或wiki时,经常会看到RSS图标,就这的意思是,当你订阅了该文章,如果后续有更新,会及时通知你。
其实,简单来讲就一句话:当一个对象变化时,其它依赖该对象的对象都会收到通知,并且随着变化!对象之间是一对多的关系。
2. the class diagram
3. 实例
import java.util.*;
public class ObserverPattern {
public static void main(String[] args){
Subject sub=new ConcreteSubject();
Observer observer1=new Observer1();
sub.registerObserver(observer1);
Observer observer2=new Observer2();
sub.registerObserver(observer2);
sub.operation();
}
}
//观察者模式
//观察者接口
interface Observer{
public void update();
}
//观察者1
class Observer1 implements Observer{
@Override
public void update(){
System.out.println("observer1 has received!");
}
}
//观察者2
class Observer2 implements Observer{
@Override
public void update(){
System.out.println("observer2 has received!");
}
}
//Subject接口
interface Subject{
public void registerObserver(Observer observer);
public void removeObserver(Observer observer);
public void notifyObserver();
public void operation();
}
//Subject实现类
class ConcreteSubject implements Subject{
private Vector<Observer> observers=new Vector<Observer>();
@Override
public void registerObserver(Observer observer){
observers.add(observer);
}
@Override
public void removeObserver(Observer observer){
observers.remove(observer);
}
@Override
public void notifyObserver(){
for(Observer obs:observers){
obs.update();
}
}
@Override
public void operation(){
System.out.println("subject changed!");
this.notifyObserver();
}
}
输出
subject changed!
observer1 has received!
observer2 has received!