• 设计模式---观察者模式(学习笔记)


    定义观察者模式:当一个主题对象(或者可以在浏览器)当状态更改。其他吸毒者(观察员)您将会收到通知。

    下面Demo它是基于Java jar包观察者写:

    对象的代码部分:

    import java.util.Observable;
    
    public class ObserverSubject extends Observable {
    
    	public ObserverSubject() {
    		super();
    		// TODO Auto-generated constructor stub
    	}
    
    	public void sendNotify(String content){
    		setChanged();
    		notifyObservers(content);
    	}
    }
    
    两个依赖者的代码部分:

    依赖者一的代码:

    import java.util.Observable;
    import java.util.Observer;
    
    public class ReceverOne implements Observer {
    
    	Observable observable;
    	
    	public ReceverOne(Observable observable) {
    		super();
    		this.observable = observable;
    		this.observable.addObserver(this);
    	}
    
    	@Override
    	public void update(Observable o, Object arg) {
    		// TODO Auto-generated method stub
    		if(o instanceof ObserverSubject){
    			   System.out.println("I am ReceverOne,I have receiver:"+arg.toString());
    		}
         
    	}
    
    }
    依赖者二的代码
    import java.util.Observable;
    import java.util.Observer;
    
    public class ReceverTwo implements Observer {
    
    	Observable observable;
    	
    	public ReceverTwo(Observable observable) {
    		super();
    		this.observable = observable;
    		this.observable.addObserver(this);
    	}
    
    	@Override
    	public void update(Observable o, Object arg) {
    		// TODO Auto-generated method stub
    		if(o instanceof ObserverSubject){
    			   System.out.println("I am ReceverTwo,I have receiver:"+arg.toString());
    		}
         
    	}
    
    }
    发送一个消息測试这个观察者模式:
    	public static void main(String[] args) {
    		// TODO Auto-generated method stub
            ObserverSubject observer=new ObserverSubject();
            new ReceverOne(observer);
            new ReceverTwo(observer);
            observer.sendNotify("Hello ,this is the first notifition");
            
     
    	}
    
    以上代码执行的结果为:

    I am ReceverTwo,I have receiver:Hello ,this is the first notifition
    I am ReceverOne,I have receiver:Hello ,this is the first notifition

    看结果可知:编程时不要依赖观察者被通知的顺序。

    接下来所介绍的是自己定义观察者模式:

    先定义要成为观察者的接口,这是主题接口,对象使用此接口注冊为观察者,或者从观察者中移除(这个是成为观察者的条件)

    public interface DefineObservAble {
    
    	void registerObserver(DefineObserver observer);
    	void removeObserver(DefineObserver observer);
    	void notifyObserver(Object o);
    }
    再定义观察者的接口,全部潜在的观察者,都必须实现这个接口----观察者接口。有通知时调用uPdate方法(这个是观察者的义务)

    public interface DefineObserver {
    
    	void update(Object o);
    }
    

     然后再创建一个详细的观察者
    public class MyObservAble implements DefineObservAble {
    
    	private ArrayList observers=null;
    	public MyObservAble(){
    		observers=new ArrayList<>();
    	}
    	@Override
    	public  void registerObserver(DefineObserver observer) {
    		// TODO Auto-generated method stub
    		if(observers==null)return;
    		 synchronized(observers){
    			int i=observers.indexOf(observer);
    			if(i==-1){
    				observers.add(observer);
    			}
    		}
    		
    
    	}
    
    	@Override
    	public void removeObserver(DefineObserver observer) {
    		// TODO Auto-generated method stub
    		if(observers==null)return;
    		synchronized (observer) {
    			int i=observers.indexOf(observer);
    			if(i!=-1){
    				observers.remove(i);
    			}
    		}
    		
    
    	}
    
    	@Override
    	public void notifyObserver(Object o) {
    		// TODO Auto-generated method stub
    		if(observers==null)return;
    		int size=observers.size();
    		for(int i=0;i<size;i++){
    			DefineObserver observer=(DefineObserver) observers.get(i);
    			observer.update(o);
    		}
    		
    
    	}
    
    	public void sendNotify(String content){
    		notifyObserver(content);
    	}
    }
    创建两个能够用于观察的类:
    public class ObserverOne implements DefineObserver {
    
    
     
    	public ObserverOne(DefineObservAble able) {
    		able.registerObserver(this);
    	}
    
    
    	@Override
    	public void update(Object o) {
    		// TODO Auto-generated method stub
           System.out.println("This is the DefineObserver,I am ObserverOne, I have receive:"+o);
    	}
    
    
    }
    public class ObserverTwo implements DefineObserver {
    
     
    	public ObserverTwo(DefineObservAble able) {
    		able.registerObserver(this);
    	}
    
    	@Override
    	public void update(Object o) {
    		// TODO Auto-generated method stub
           System.out.println("This is the DefineObserver,I am ObserverTwo, I have receive:"+o);
    	}
    
    }
    

    最后进行測试,发送一个通知:
    	/**
    	 * @param args
    	 */
    	public static void main(String[] args) {
    		// TODO Auto-generated method stub
       MyObservAble able=new MyObservAble();
       new ObserverOne(able);
       new ObserverTwo(able);
       able.sendNotify(" hello world!");
    	}
    

    哎,这个写的太乱啦!概念上不是太清楚。有书上直接写为 主题(注冊,移除,通知更新的类)和观察者(实当前update方法)分别。代码或清除

    版权声明:本文博客原创文章,博客,未经同意,不得转载。

  • 相关阅读:
    羊年春节微信数据大解析
    微信公众号推荐(自己关注的微信公众平台导航)
    微信要革"传统电视"的命吗?
    微信是在学苹果模式吗?
    发微信红包啦!借花献佛
    有原创保护能力的公众帐号可申请页面模版功能和图文消息正文插入历史群发链接
    编程能力与编程年龄
    代码执行的效率
    对九个超级程序员的采访
    编程真难啊
  • 原文地址:https://www.cnblogs.com/gcczhongduan/p/4686906.html
Copyright © 2020-2023  润新知