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+"***");
}

}