• 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。

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  • 原文地址:https://www.cnblogs.com/gcczhongduan/p/4686906.html
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