观察者模式和监听模式

观察者模式和监听模式完成的都是一样的工作就是通知的作用。我们现在试想一个案例，一个士兵在发现敌人之后需要报告长官。好的我们现在来着手写

Pawn 类

package test;

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

public class Pawn {

	
	 private List<Leader> leaders=new ArrayList<>();
	 
	 public void attach(Leader l){
		 
		 
		leaders.add(l);
		 
	 }
	 public void detach(Leader l){
		 
		 leaders.remove(l);
		 
		 
	 }
	 
	 public void standGuard( ){
		
		 System.out.println("Pawn: find enemies ,I wanna report Sir");
		if(true/*find enemies*/){
			
			for(Leader leader:leaders){
				leader.order( "find enemies");	
			}
		}
		
	}
	 

	 public static void main(String args[]){
		 
		 Pawn p=new Pawn();
		 p.attach(new Captain());
		 p.standGuard();
		 
	 }
	
}

Leader 类

package test;

public interface Leader {

	public void order(String string);
}

Captain类

package test;

public class Captain implements Leader {

	@Override
	public void order(String msg) {
		// TODO Auto-generated method stub
		System.out.println("Captain:recevie a message:"+msg);
	}

}

上面的源码就是观察者模式的简单实现。可以看见其实很简单。就是让一个类在触发某件事的时候去调用另一个类的方法

而监听模式就是在观察者和被观察者之间建立一座桥梁
leader和Caption类没有变
Pawn 类

package listener;

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


public class Pawn {

	 private List<Leader> leaders=new ArrayList<>();
	 private List<Listener> listeners=new ArrayList<>();
	 
	 public  Pawn(){
		 
		 attach(new Captain());
		 addListener(new Listener(){

				@Override
				public void handleEvent(EventString es) {
					// TODO Auto-generated method stub
					
					for(Leader leader:leaders){
						leader.order(es.getMsg());	
					}
				}
				 
			 });
		
	 }
	 public void attach(Leader l){
		 
		 
			leaders.add(l);
			 
	}
	public void detach(Leader l){
			 
			 leaders.remove(l);
			 
			 
	}
	 public void addListener(Listener l){
		 
		 
		 listeners.add(l);
		 
	 }
	 public void removeListener(Listener l){
		 
		 listeners.remove(l);
		 
		 
	 }
	 
	 public void standGuard( ){
		
		 System.out.println("Pawn: find enemies ,I wanna report Sir");
		if(true/*find enemies*/){
			
			EventString e=new EventString("find enemies: type =footman");
			
			for(Listener l:listeners){
				l.handleEvent(e);
			}
		}
		
	}
	 

	 public static void main(String args[]){
		 
		 Pawn p=new Pawn();
	
		 p.standGuard();
		 
	 }
	
}

listener类

package listener;

public interface Listener {

	public void  handleEvent(EventString e);
	
}

EventString类

package listener;

public class EventString  {

	private String msg;

	public EventString(String msg) {
		super();
		this.msg = msg;
	}

	public String getMsg() {
		return msg;
	}

	public void setMsg(String msg) {
		this.msg = msg;
	}
	
	
	
	
	
}

我们可以发现 使用监听之后我们就可以分离观察者和被观察者了