观察者模式

package observer;

public interface Observer {
	void update(Subject subject);
}

class ObserverA implements Observer{

	private int mystate;//保持和目标者状态一致
	
	@Override
	public void update(Subject subject) {
		// TODO Auto-generated method stub
		this.mystate = ((ConcreteSubject)subject).getState();
		
	}

	public int getMystate() {
		return mystate;
	}

	public void setMystate(int mystate) {
		this.mystate = mystate;
	}
	
	
}

package observer;

import java.util.ArrayList;
import java.util.List;

public class Subject {
	protected List<Observer> list = new ArrayList<Observer>();
	
	public void register(Observer observer) {
		list.add(observer);
	}
	
	//通知所有观察者
	public void notifyAllObserver() {
		for (Observer observer : list) {
			observer.update(this);
		}
	}
}

package observer;

public class ConcreteSubject extends Subject{
	private int state;

	public int getState() {
		return state;
	}
	//状态改变，就调用通知所有观察者方法
	public void setState(int state) {
		this.state = state;
		this.notifyAllObserver();
	}
	
	
	
}

package observer;

public class Client {
	public static void main(String[] args) {
		//目标对象
		ConcreteSubject sub = new ConcreteSubject();
		
		//创建多个观察者 
		ObserverA o1 = new ObserverA();
		ObserverA o2 = new ObserverA();
		ObserverA o3 = new ObserverA();
		
		//将这三个对象添加到subject容器中
		sub.register(o1);
		sub.register(o2);
		sub.register(o3);
		
		//改变目标对象状态
		sub.setState(1000);
		
		
		//查看观察者是否改变
		System.out.println(o1.getMystate());
		System.out.println(o2.getMystate());
		System.out.println(o3.getMystate());
		
	}
}