观察者模式

package observer;
import java.util.*;
public class ObserverPattern
{
    public static void main(String[] args)
    {
        Subject subject=new ConcreteSubject();
        Observer obs1=new ConcreteObserver1();
        Observer obs2=new ConcreteObserver2();
        subject.add(obs1);
        subject.add(obs2);
        subject.notifyObserver();
    }
}
//抽象目标
abstract class Subject
{
    protected List<Observer> observers=new ArrayList<Observer>();   
    //增加观察者方法
    public void add(Observer observer)
    {
        observers.add(observer);
    }    
    //删除观察者方法
    public void remove(Observer observer)
    {
        observers.remove(observer);
    }   
    public abstract void notifyObserver(); //通知观察者方法
}
//具体目标
class ConcreteSubject extends Subject
{
    public void notifyObserver()
    {
        System.out.println("具体目标发生改变...");
        System.out.println("--------------");       
       
        for(Object obs:observers)
        {
            ((Observer)obs).response();
        }
       
    }          
}
//抽象观察者
interface Observer
{
    void response(); //反应
}
//具体观察者1
class ConcreteObserver1 implements Observer
{
    public void response()
    {
        System.out.println("具体观察者1作出反应！");
    }
}
//具体观察者1
class ConcreteObserver2 implements Observer
{
    public void response()
    {
        System.out.println("具体观察者2作出反应！");
    }
}