观察者模式示例和分析 - 示例 1：猫、狗和老鼠

假设猫是老鼠和狗的观察目标，老鼠和狗是观察者，猫叫老鼠跑，狗也跟着叫，使用观察者模式描述该过程。

 

public class Cat extends MySubject
{
	public void cry()
	{
		System.out.println("猫叫！");
		System.out.println("----------------------------");		
		
		for(Object obs:observers)
		{
			((MyObserver)obs).response();
		}
		
	}	   	
}

public class Client
{
	public static void main(String a[])
	{
		MySubject subject=new Cat();
		
		MyObserver obs1,obs2,obs3;
		obs1=new Mouse();
		obs2=new Mouse();
		obs3=new Dog();
		
		subject.attach(obs1);
		subject.attach(obs2);
		subject.attach(obs3);
		
		MyObserver obs4;
		obs4=new Pig();
		subject.attach(obs4);
		
		subject.cry();		
	}
}

public class Dog implements MyObserver
{
	public void response()
	{
		System.out.println("狗跟着叫！");
	}	
}

public class Mouse implements MyObserver
{
	public void response()
	{
		System.out.println("老鼠努力逃跑！");
	}
}

public interface MyObserver
{
	void response();  //抽象响应方法
}

import java.util.*;

public abstract class MySubject
{
	protected ArrayList observers = new ArrayList();
	
	//注册方法
	public void attach(MyObserver observer)
	{
		observers.add(observer);
	} 
	
	//注销方法
	public void detach(MyObserver observer)
	{
		observers.remove(observer);
	}
	
	public abstract void cry(); //抽象通知方法
}

public class Pig implements MyObserver
{
	public void response()
	{
		System.out.println("猪没有反应！");
	}	
}