观察者模式

Posted 2022-06-22 自行车在路上

在对象之间定义一对多的依赖，当一个对象改变状态，依赖它的对象都会接受到通知，并自动更新性能

文章目录

• 观察者模式类图
• 场景解读
• 代码展示
• • 天气数据的接口和模型
  • 观察者
  • 测试类
  • 总结：
• 代码github连接

观察者模式类图

场景解读

场景：天气预报的天气温度，湿度，气压会不断的变化，但是每个的天气预报的显示这三个参数的形式会是不同的，如有的预报会用很详细的说明信息显示，有的只是显示普通数值

解析以下类图，
StatisticsDisplay和CurrentConditionsDisplay显示方式不同
StatisticsDisplay显示的是跟踪最小、平均、最大的观测值，并显示他们
CurrentConditionsDisplay显示当前观测值
当新建StatisticsDisplay，CurrentConditionsDisplay时放将他们weatherData的对象集合里面，当天气数据更改时则更新StatisticsDisplay，CurrentConditionsDisplay里显示方式的值。

代码展示

天气数据的接口和模型

管理类-注册对象，移除对象，通知对象接口
Subject

package observerMode.weatherModel;
/**
 * 管理类
 * @Date:Created in  15:36 2019/6/1
 */
public interface Subject 
    public void registerObServer(Observer o);
    public void removeObserver(Observer o);
    public void notifyObserver();

WeatherData-实现

package observerMode.weatherModel;

import observerMode.displayModel.Observer;

import java.util.ArrayList;

/**
 * @Author:zhanCai
 * @Description:
 * @Date:Created in  15:47 2019/6/1
 * @Modified by
 * 天气数据
 */
public class WeatherData implements Subject 
    private ArrayList observers;
    private float temperature;
    private float humidity;
    private float pressure;

    public WeatherData() 
        this.observers = new ArrayList();
    

    @Override
    public void registerObServer(Observer o) 
        observers.add(o);
    

    @Override
    public void removeObserver(Observer o) 
        int i = observers.indexOf(o);
        if(i>=0)
            observers.remove(i);
        
    

    @Override
    //通知观察者
    public void notifyObserver() 
        for (int i = 0; i < observers.size(); i++) 
            Observer observer = (Observer) observers.get(i);
            observer.update(temperature,humidity,pressure);
        
    

    public void messurementsChanged()
        notifyObserver();
    
    //温度变化
    public void setMessurements(float temperature,float humidity,float pressure)
        this.temperature = temperature;
        this.humidity = humidity;
        this.pressure = pressure;
        messurementsChanged();
    

观察者

观察者对象接口
Observer-更新数据

package observerMode.displayModel;
public interface Observer 
    public void update(float temp,float humidity,float preesure);

DisplayElement-显示接口

package observerMode.displayModel;
public interface DisplayElement 
    public void display();

CurrentConditionsDisplay观察者实现

package observerMode.displayModel;
import observerMode.weatherModel.Subject;
/**
 * CurrentConditionsDisplay显示当前观测值
 */
public class CurrentConditionsDisplay implements Observer,DisplayElement 
    private float temperature;
    private float humidity;
    private float preesure;
    private Subject weatherData;

    public CurrentConditionsDisplay(Subject weatherData) 
        this.weatherData = weatherData;
        weatherData.registerObServer(this);
    
    public void display() 
        System.out.println("Current conditions:"+temperature+"F degrees and "+humidity+" % humidity");
    
    public void update(float temperature, float humidity, float pressure) 
        this.temperature = temperature;
        this.humidity = humidity;
        this.preesure = pressure;
        display();
    

StatisticsDisplay观察者实现

package observerMode.displayModel;
import observerMode.weatherModel.Subject;
/**
 * StatisticsDisplay显示的是跟踪最小、平均、最大的观测值，并显示他们
 */
public class StatisticsDisplay implements Observer,DisplayElement 
    private float temperature;
    private float humidity;
    private float preesure;
    private Subject weatherData;
    public StatisticsDisplay(Subject weatherData) 
        this.weatherData = weatherData;
        weatherData.registerObServer(this);
    
    @Override
    public void display() 
        System.out.println("temperature is "+temperature+" and humidity is "+humidity);
    
    @Override
    public void update(float temperature, float humidity, float pressure) 
        this.temperature = temperature;
        this.humidity = humidity;
        this.preesure = pressure;
        display();
    

测试类

package observerMode.action;
import observerMode.displayModel.CurrentConditionsDisplay;
import observerMode.displayModel.StatisticsDisplay;
import observerMode.weatherModel.WeatherData;
import org.junit.Test;
/**
 * @Date:Created in  16:07 2019/6/1
 */
public class WeatherStation 
    @Test
    public void testWeatherObserver()
        WeatherData weatherData = new WeatherData();

        CurrentConditionsDisplay currentConditionsDisplay = new CurrentConditionsDisplay(weatherData);
        StatisticsDisplay statisticsDisplay = new StatisticsDisplay(weatherData);
        weatherData.setMessurements(33,44,55);
        weatherData.setMessurements(66,77,88);
    

结果输出

Current conditions:33.0F degrees and 44.0 % humidity
temperature is 33.0 and humidity is 44.0
Current conditions:66.0F degrees and 77.0 % humidity
temperature is 66.0 and humidity is 77.0

总结：

总的来说，观察者模式看类图完全没有实现的嵌入，实现的代码都已接口去调用，这感觉很棒，低耦合。

代码github连接

https://github.com/sky5cai/DesignModeTest