java设计模式之观察者模式简单解读

package com.wanmei.meishu.ms;

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

//观察者接口
interface Observable{
	//观察
	void addSub(ISubject sub);
	//取消观察
	void removeSub(ISubject sub,String msg);
	//读取消息
	void watch(String msg);
	//获取观察者名称
	String getName();
}
//观察者实例
class Observer implements Observable {
	private String name;
	public Observer(String name) {
		this.name = name;
	}
	@Override
	public void addSub(ISubject sub){
		sub.addObserver(this);
		System.out.println("Observer:用户【"+this.name+"】 订阅了消息");
	}
	@Override
	public void removeSub(ISubject sub,String msg){
		sub.removeObserver(this);
		System.out.println("Observer:用户【"+this.name+"】 取消了订阅消息," + (msg == null ? "" : ("并说：" + msg)));
	}
	@Override
	public void watch(String msg) {
		System.out.println("Observer:用户【"+this.name+"】读取到的订阅消息是：" + msg);
	}
	
	public String getName() {
		return name;
	}
}

//被观察者接口
interface ISubject{
	//给观察者们发送消息
	void sendMsg(String msg);
	//添加一个观察者
	void addObserver(Observable user);
	//取消一个观察者
	void removeObserver(Observable user);
}

//被观察者实现方式
class SubjectImpl implements ISubject{
	
	//持有观察者队列
	private List<Observable> observerList;

	//添加一个观察者
	public synchronized void addObserver(Observable user){
		if(observerList == null){
			observerList = new ArrayList<Observable>();
		}
		observerList.add(user);
		String str = "";
		for (Observable observable : observerList) {
			str+= observable.getName()+"、";
		}
		System.out.println("ISubject:目前已有用户：" + str.substring(0, str.length()-1));
	}
	//取消一个观察者
	public void removeObserver(Observable user){
		observerList.remove(user);
		if(!observerList.isEmpty()){
			String str = "";
			for (Observable observable : observerList) {
				str+= observable.getName()+"、";
			}
			System.out.println("ISubject:目前剩余用户：" + str.substring(0, str.length()- 1));
		}
	}
	@Override
	public void sendMsg(String msg) {
		if(!observerList.isEmpty()){
			System.out.println("ISubject:发送消息：" + msg);
			for (Observable observable : observerList) {
				observable.watch(msg);
			}
		}
	}
	
}

public class ObserverTest {

	public static void main(String[] args) {
		ISubject sub = new SubjectImpl();
		//第一个观察者
		Observable u1 = new Observer("吴文俊");
		u1.addSub(sub);
		Observable u2 = new Observer("吴华云");
		u2.addSub(sub);
		Observable u3 = new Observer("李爪哇");
		u3.addSub(sub);
		sub.sendMsg("PHP是世界上最好的语言！");
		u3.removeSub(sub,"去死吧，PHP");
		sub.sendMsg("PHP是世界上最好的语言！");
		
		
	}
}