设计模式--观察者模式

Internet气象站项目：

　　提供温度、气压和湿度的接口

　　测量数据更新时需时时通知给第三方 需要设计开放型API，便于其他第三方公司也能接入气象站获取数据

WeatherData类

　　

一个通常的设计方案

　　

代码演示：

WeatherData类

package com.java.hexter.internetweather;

public class WeatherData {
    
    private float mTemperatrue;
    private float mPressure;
    private float mHumidity;
    private CurrentConditions mCurrentConditions;
    public WeatherData(CurrentConditions mCurrentConditions)
    {
    　　this. mCurrentConditions= mCurrentConditions;
    }
    
    public float getTemperature()
    {
        return mTemperatrue;   
    }
    
    public float getPressure()
    {
        return mPressure;    
    }
    
    public float getHumidity()
    {
        return mHumidity;  
    }
    public void dataChange()
    {
        mCurrentConditions.update(getTemperature(), getPressure(), getHumidity());
    }
    
    public void setData(float mTemperature,float mPressure,float mHumidity)
    {
        this.mTemperatrue=mTemperature;
        this.mPressure=mPressure;
        this.mHumidity=mHumidity;
        dataChange();
    }
    
}

 代表第三方的类

package com.java.hexter.internetweather;

public class CurrentConditions {
    
    private float mTemperature;
    private float mPressure;
    private float mHumidity;
    
    public void update(float mTemperature,float mPressure,float mHumidity)
    {
        this.mTemperature=mTemperature;
        this.mPressure=mPressure;
        this.mHumidity=mHumidity;
        display();
    }
    
    public void display()
    {
        System.out.println("***Today mTemperature: "+mTemperature+"***");
        System.out.println("***Today mPressure: "+mPressure+"***");
        System.out.println("***Today mHumidity: "+mHumidity+"***");
    }
}

有些问题

　　1）其他第三方公司接入气象站获取数据的问题

　　2）无法在运行时动态的添加第三方

观察者模式原理

观察者模式就像定牛奶业务

　　1）奶站，Subject

　　2）用户，Observer

Subject：登记注册、移除和通知

　　

Observer：接收输入

　　

观察者模式： 对象之间多对一依赖的一种设计方案，被依赖的对象为Subject，依赖的对象为Observer，Subject通知Observer变化

用观察者模式设计重新设计的方案

　　

代码演示：　

package com.java.hexter.internetweather.observer;

public interface Subject {
    public void registerObserver(Observer o);
    public void removeObserver(Observer o);
    public void notifyObservers();
}

package com.java.hexter.internetweather.observer;

public interface Observer {
    public void update(float mTemperatrue,float mPressure,float mHumidity);
}

package com.java.hexter.internetweather.mode;

import java.util.ArrayList;

import com.java.hexter.internetweather.observer.Observer;
import com.java.hexter.internetweather.observer.Subject;

public class WeatherDataSt implements Subject{
    
    private float mTemperatrue;
    private float mPressure;
    private float mHumidity;
    private ArrayList<Observer> mObservers;
    public WeatherDataSt()
    {
        mObservers=new ArrayList<Observer>();
    }
    
    public float getTemperature()
    {
        return mTemperatrue;
        
    }
    public float getPressure()
    {
        return mPressure;    
    }
    
    public float getHumidity()
    {
        return mHumidity;    
    }
    public void dataChange()
    {
        notifyObservers();
    }
    
    public void setData(float mTemperatrue,float mPressure,float mHumidity)
    {
        this.mTemperatrue=mTemperatrue;
        this.mPressure=mPressure;
        this.mHumidity=mHumidity;
        dataChange();
    }

    @Override
    public void registerObserver(Observer o) {
        // TODO Auto-generated method stub
        mObservers.add(o);
    }

    @Override
    public void removeObserver(Observer o) {
        // TODO Auto-generated method stub
        if(mObservers.contains(o))
        {mObservers.remove(o);}
    }

    @Override
    public void notifyObservers() {
        // TODO Auto-generated method stub
        for(int i=0,len=mObservers.size();i<len;i++)
        {
            mObservers.get(i).update(getTemperature(), getPressure(), getHumidity());
        }
    }

}

package com.java.hexter.internetweather.mode;

import com.java.hexter.internetweather.observer.Observer;

public class CurrentConditions implements Observer {//可以有多个子类代表多个第三方

    private float mTemperatrue;
    private float mPressure;
    private float mHumidity;

    @Override
    public void update(float mTemperatrue, float mPressure, float mHumidity) {
        // TODO Auto-generated method stub
        this.mHumidity = mHumidity;
        this.mPressure = mPressure;
        this.mTemperatrue = mTemperatrue;
        display();
    }

    public void display() {
        System.out.println("***Today mTemperatrue:" + mTemperatrue + "***");
        System.out.println("***Today mPressure:" + mPressure + "***");
        System.out.println("***Today mHumidity:" + mHumidity + "***");
    }

}

Java内置的观察者 Observable Observer

用Java内置观察者重新设计该项目

内置观察者的注意点 　　Observable是类而不是接口

代码如下：

package com.java.hexter.internetweather.jv;

import java.util.Observable;

public class WeatherData extends Observable{
    private float mTemperatrue;
    private float mPressure;
    private float mHumidity;
    
    public float getTemperature()
    {
        return mTemperatrue;
    }
    
    public float getPressure()
    {
        return mPressure;  
    }
    
    public float getHumidity()
    {
        return mHumidity;    
    }
    
    
    public void dataChange()
    {
        this.setChanged();
        this.notifyObservers(new Data(getTemperature(),getPressure(),getHumidity()));
        
    }
    
    
    public void setData(float mTemperatrue,float mPressure,float mHumidity)
    {
        this.mTemperatrue=mTemperatrue;
        this.mPressure=mPressure;
        this.mHumidity=mHumidity;
        dataChange();
    }
    
    public class Data
    {
        public float mTemperatrue;
        public float mPressure;
        public float mHumidity;
        public Data(float mTemperatrue,float mPressure,float mHumidity)
        {
            this.mTemperatrue=mTemperatrue;
            this.mPressure=mPressure;
            this.mHumidity=mHumidity;
        }
    }
    
}

package com.java.hexter.internetweather.jv;

import java.util.Observable;
import java.util.Observer;

import com.java.hexter.internetweather.jv.WeatherData.Data;


public class CurrentConditions implements Observer {
    
    private float mTemperatrue;
    private float mPressure;
    private float mHumidity;
    @Override
    public void update(Observable arg0, Object arg1) {
        // TODO Auto-generated method stub
        this.mTemperatrue=((Data)(arg1)).mTemperatrue;
        this.mPressure=((Data)(arg1)).mPressure;
        this.mHumidity=((Data)(arg1)).mHumidity;
        display();
    }
    
    public void display()
    {
        System.out.println("***Today mTemperatrue:" +mTemperatrue+"***");
        System.out.println("***Today mPressure:" +mPressure+"***");
        System.out.println("***Today mHumidity:" +mHumidity+"***");
    }
    
    
}