JAVA設計模式學習筆記-觀察者模式

觀察者模式：對象之間多對一依賴的一種設計方案，被依賴的對象爲Subject，依賴的對象爲Observer，Subject通知Observer變化java

生活中的例子就是：訂報紙、頂牛奶dom

案例一:氣象站一個普通的方案： ide

氣象站類測試

package com.java.test.internetweather;

import java.util.Observable;


public class WeatherData extends Observable {
	//氣象站的信息
    //溫度氣壓溼度
	private float mTemperatrue;
	private float mPressure;
	private float mHumidity;

    //外部接入的類
    //公告板類
    //須要得到氣象站的這些信息，而且氣象站的信息變化，也要跟着變
	private CurrentConditions mCurrentConditions;

    //有參構造，須要傳入公告板類
	public WeatherData(CurrentConditions mCurrentConditions)
	{
		this. mCurrentConditions= mCurrentConditions;
	}
	
    //三個get方法
	public float getTemperature()
	{
		return mTemperatrue;	
	}
	public float getPressure()
	{
		return mPressure;
		
	}
	public float getHumidity()
	{
		return mHumidity;

    //處理數據變化，數據變化，也要把變化的數據傳入公告板類，實現跟着變
	}
	public void dataChange()
	{
		mCurrentConditions.update(this.getTemperature(),this.getPressure(),this.getHumidity());
	}
	
    //設定數據
	public void setData(float mTemperature,float mPressure,float mHumidity)
	{
		this.mTemperatrue=mTemperature;
		this.mPressure=mPressure;
		this.mHumidity=mHumidity;
		dataChange();
	}
}

//公告板類
```java
package com.java.test.internetweather;


public class CurrentConditions {

	//定義溫度氣壓溼度
	private float mTemperature;
	private float mPressure;
	private float mHumidity;

	//設定三個參數
	public void update(float mTemperature,float mPressure,float mHumidity)
	{
		this.mTemperature=mTemperature;
		this.mPressure=mPressure;
		this.mHumidity=mHumidity;
		display();
	}

	//展現數據，在控制檯模擬
	public void display()
	{
		System.out.println("***Today mTemperature: "+mTemperature+"***");
		System.out.println("***Today mPressure: "+mPressure+"***");
		System.out.println("***Today mHumidity: "+mHumidity+"***");
	}
}

//測試類
```java
package com.java.test.internetweather;

public class InternetWeather {

	public static void main(String[] args) {
		CurrentConditions mCurrentConditions;
		WeatherData mWeatherData;
		
		mCurrentConditions=new CurrentConditions();
		mWeatherData=new WeatherData(mCurrentConditions);
		
		mWeatherData.setData(30, 150, 40);
	}
}

這種方式耦合性仍是過高this

觀察者模式設計方案設計

Subject接口類code

package com.java.test.internetweather.observer;

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

Observerserver

package com.java.test.internetweather.observer;

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

公告牌一 CurrentConditions對象

package com.java.test.internetweather.mode;

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

public class CurrentConditions implements Observer {

	/*私有變量*/
	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 + "***");
	}
}

公告牌二 ForcastConditionsblog

package com.java.test.internetweather.mode;

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


public class ForcastConditions implements Observer{
	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.mTemperatrue=mTemperatrue;
		this.mPressure=mPressure;
		this.mHumidity=mHumidity;
		
		display();
	}
	public void display()
	{
		System.out.println("**明天溫度:"+(mTemperatrue+Math.random())+"**");
		System.out.println("**明天氣壓:"+(mPressure+10*Math.random())+"**");
		System.out.println("**明天溼度:"+(mHumidity+Math.random())+"**");
	}
}

測試類 InternetWeather

package com.java.test.internetweather.mode;



public class InternetWeather {

	public static void main(String[] args) {
		
		CurrentConditions mCurrentConditions;
		ForcastConditions mForcastConditions;
		WeatherDataSt mWeatherDataSt;
		
		mWeatherDataSt=new WeatherDataSt();
		mCurrentConditions=new CurrentConditions();
		mForcastConditions=new ForcastConditions();
		
		mWeatherDataSt.registerObserver(mCurrentConditions);
		mWeatherDataSt.registerObserver(mForcastConditions);
		
		mWeatherDataSt.setData(30, 150, 40);
		mWeatherDataSt.removeObserver(mCurrentConditions);
		mWeatherDataSt.setData(40, 250, 50);
	}
}

觀察者模式實現了比較好的低耦合特性，Object和Observer之間的關係只有實現了update方法這一關係，耦合性很是低

Java內置了觀察者對象 Observable Observer

Subject

WeatherData

package com.java.test.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()
	{
		//表示數據變化了
		//從源碼中能夠看到裏面有個bool值變爲了true，下面那個方法會判斷這個是否爲true
		this.setChanged();
		//這個方式是等觀察者本身拉取
		//this.notifyObservers();
		//這個方式是把信息主動推送給觀察者
		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;
		}
	}	
}

公告板一

package com.java.test.internetweather.jv;

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

import com.java.test.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+"***");
	}
	
	
}

公告板二 ForcastConditions

package com.java.test.internetweather.mode;

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


public class ForcastConditions implements Observer{
	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.mTemperatrue=mTemperatrue;
		this.mPressure=mPressure;
		this.mHumidity=mHumidity;
		
		display();
	}
	public void display()
	{
		System.out.println("**明天溫度:"+(mTemperatrue+Math.random())+"**");
		System.out.println("**明天氣壓:"+(mPressure+10*Math.random())+"**");
		System.out.println("**明天溼度:"+(mHumidity+Math.random())+"**");
	}
}

測試類

package com.java.test.internetweather.jv;

public class InternetWeather {
	public static void main(String[] args) {
		CurrentConditions mCurrentConditions;
		ForcastConditions mForcastConditions;
		WeatherData mWeatherData;
		 
		mCurrentConditions=new CurrentConditions();
		mForcastConditions=new ForcastConditions();
		mWeatherData=new WeatherData();
		
		mWeatherData.addObserver(mCurrentConditions);
		mWeatherData.addObserver(mForcastConditions);
		mWeatherData.setData(30, 150, 40);
		
		mWeatherData.deleteObserver(mCurrentConditions);
		mWeatherData.setData(35, 150, 60);
		
	}
}