Head First设计模式二---观察者模式

   观察者模式---在对象之间以多对一的依赖，这样一来，当一个对象改变状态，依赖它的对象都会收到通知，并自动更新.

   书中以报社和订报者来形容,真是恰到好处(也有注册,删除,通知等功能)!

   首先是主题接口(也即被观察者接口),其中定义了注册,删除,通知观察者等方法:

 

 package com.jie.observer;

public interface Subject {

	public void registerObserver(Observer o);
	public void removeObserver(Observer o);
	public void notifyObservers();
}

  接着是被观察者(也即被依赖者,其实现了上面的接口):

  

package com.jie.observer;

import java.util.*;

public class WeatherData implements Subject{

	private ArrayList observers;
	private float temperature;
	private float humidity;
	private float pressure;
	
	public WeatherData()
	{
		observers=new ArrayList();
	}
	
	public void registerObserver(Observer o)
	{
		observers.add(o);
	}
	
	public void removeObserver(Observer o)
	{
	    int i=observers.indexOf(o);
	    if(i>=0)
	    {
	    	observers.remove(i);
	    }
	}
	
	public void notifyObservers()
	{
		for(int i=0;i<observers.size();i++)
		{
			Observer observer=(Observer)observers.get(i);
			observer.update(temperature,humidity,pressure);
		}
	}
	
	public void measurementsChanged()
	{
		notifyObservers();
	}
	
	public void setMeasurements(float temperature,float humidity,float pressure)
	{
	    this.temperature=temperature;
	    this.humidity=humidity;
	    this.pressure=pressure;
	    measurementsChanged();
	    
	}
}

  跟着就是观察者接口:

 

 package com.jie.observer;

public interface Observer {

	public void update(float temperature,float humidity,float pressure);
}

   接着当然观察者(实现了上面的观察者接口):

  

package com.jie.observer;

public class CurrentConditionsDisplay implements Observer,DisplayElement{
	
	private float temperature;
	private float humidity;
	private float pressure;
	private Subject weatherData;
	
	public CurrentConditionsDisplay(Subject weatherData)
	{
		this.weatherData=weatherData;
		weatherData.registerObserver(this);
	}
	
    public void update(float temperature,float humidity,float pressure)
    {
    	this.temperature=temperature;
    	this.humidity=humidity;
    	this.pressure=pressure;
    	display();
    }
    
    public void display()
    {
    	System.out.println("Current conditions:"+temperature+"F degrees and "+
    			humidity+"% humidity "+pressure+" pressure");
    }
}

   最后少不了一个测试类:

  

package com.jie.observer;

public class Test {

	public static void  main(String [] args)
	{
		WeatherData wd=new WeatherData();
		CurrentConditionsDisplay ccd=new CurrentConditionsDisplay(wd);
		wd.setMeasurements(21, 13, 30.4f);
		wd.setMeasurements(1, 2, 3f);
		
	}
}

  其中也用到了一个显示信息的接口,对模式没什么影响,一并赋上:
 
 

package com.jie.observer;

public interface DisplayElement {

	public void display();
}

评论

4 楼 scnujie 2008-03-31  

http://tk.cn.yahoo.com/a/r7DXS%2BuwfA%3D%3D

3 楼 scnujie 2008-03-31  

http://tk.cn.yahoo.com/a/r7DXS%2BuwfA%3D%3D

2 楼 scnujie 2008-03-26  

我尽量吧.不过最近时间好像不是很多！

1 楼 kunlunx 2008-03-26  

看完了都发出来，俺们就不用再去看那本厚书了