观察者模式和监听模式

骑猪看日落 2022-06-03 08:23 203阅读 0赞

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