设计模式之二：观察者模式(简单实现(气象站模拟流程))

观察者模式：定义了对象之间的一对多依赖，这样一来，当一个对象改变状态时，它的所有依赖者都会收到通知并自动更新。 当你试图勾勒观察者模式时，可以利用报纸订阅服务，以及出版者和订阅者比拟这一切。

设计原则：为了交互对象之间的松耦合设计为努力。

工程名称：SubjectAndObsever(eclipse) 下载目录：http://www.cnblogs.com/jrsmith/admin/Files.aspx ， SubjectAndObsever.zip

package com.jyu.interfaces;

/**
 * 主题接口
 * @author JRSmith
 *
 */
public interface Subject {

    /**注册观察者*/
    public void registerObsever(Obsever obsever);
    /**撤销观察者*/
    public void removeObsever(Obsever obsever);
    /**通知观察者*/
    public void notifyObsever();
}

package com.jyu.interfaces;

/**
 * 观察者接口
 * @author JRSmith
 *
 */
public interface Obsever {
    /**当气象观测值改变时，主题会把这些状态值当做方法的参数，传送给观察者*/
    public void update(float temp,float humidity,float pressure);
}

package com.jyu.interfaces;

/**
 * 布告板接口
 * @author JRSmith
 *
 */
public interface DisplayElement {
    /**当布告板需要显示时，调用此方法*/
    public void display();
}

package com.jyu.implement;

import java.util.ArrayList;
import java.util.List;

import com.jyu.interfaces.Obsever;
import com.jyu.interfaces.Subject;

public class WeatherData implements Subject {

    private List<Obsever> obsevers;
    private float temperature;
    private float humidity;
    private float pressure;
    
    public WeatherData(){
        obsevers = new ArrayList<Obsever>();
    }
    
    @Override
    public void registerObsever(Obsever obsever) {
        obsevers.add(obsever);
    }

    @Override
    public void removeObsever(Obsever obsever) {
        int i = obsevers.indexOf(obsever);
        if(i>=0){
            obsevers.remove(i);
        }
    }

    @Override
    public void notifyObsever() {
        int size = obsevers.size();
        for(int i = 0; i< size; i++){
            Obsever obsever = obsevers.get(i);
            obsever.update(temperature, humidity, pressure);
        }
    }

    /**
     * 当从气象站得到更新观测值时，我们通知观测者
     */
    public void measurementsChanged(){
        notifyObsever();
    }
    
    public void setMeasurements(float temperature,float humidity,float pressure){
        this.temperature = temperature;
        this.humidity = humidity;
        this.pressure = pressure;
        measurementsChanged();
    }
}

package com.jyu.implement;

import com.jyu.interfaces.DisplayElement;
import com.jyu.interfaces.Obsever;
import com.jyu.interfaces.Subject;

public class CurrentConditionDisplay implements Obsever, DisplayElement {

    private float temperature;
    private float humidity;
    private Subject weatherData;
    
    /**构造器需要weatherData对象(也就是主题)作为注册之用*/
    public CurrentConditionDisplay(Subject weatherData){
        this.weatherData = weatherData;
        weatherData.registerObsever(this);
    }
    

    @Override
    public void update(float temp, float humidity, float pressure) {
        this.temperature = temp;
        this.humidity = humidity;
        display();
    }

    @Override
    public void display() {
        System.out.println("Currnet conditions:"+temperature+"F degree and "+humidity+"%humidity");
    }
}

package com.jyu.test;

import com.jyu.implement.CurrentConditionDisplay;
import com.jyu.implement.WeatherData;

public class WeatherStation {

    /**
     * @param args
     */
    public static void main(String[] args) {
        WeatherData weatherData = new WeatherData();
        
        CurrentConditionDisplay currentConditionDisplay = new CurrentConditionDisplay(weatherData);
        
        weatherData.setMeasurements(80, 65, 30.4f);
    }

}