观察者模式-气象站

旧城等待， 2023-06-05 11:20 15阅读 0赞

观察者模式，在对象之间定义一对多的依赖，这样一来，当一个对象改变状态，依赖它的对象都会收到通知，并自动更新。

1、代码结构：

![SouthEast][]

package observer;
    
    /**
     * 观察者接口
     */
    public interface Observer {
    	
    	/**
    	 * 当气象观测值改变时，主题会把这些状态值当作方法的参数，传递给观察者
    	 * @param temp 温度
    	 * @param humidity 湿度
    	 * @param pressure 气压
    	 */
    	public void update(float temp, float humidity, float pressure);
    }

package observer;
    
    /**
     * 布告板
     */
    public interface DisplayElement {
    
    	/**
    	 * 当布告板需要显示时，调用此方法
    	 */
    	public void display();
    }

package observer;
    
    /**
     * 主题
     */
    public interface Subject {
    	
    	/**
    	 * 注册一个观察者
    	 * @param o
    	 */
    	public void registerObserver(Observer o);
    	
    	/**
    	 * 删除一个观察者
    	 * @param o
    	 */
    	public void removeObserver(Observer o);
    	
    	/**
    	 * 当主题改变的时，这个方法会被调用，以通知所有的观察者
    	 */
    	public void notifyObservers();
    }

package observer;
    
    import java.util.ArrayList;
    
    /**
     * 天气数据推送
     */
    public class WeatherData implements Subject{
    
    	private ArrayList<Observer> observers;//观察者们
    	private float temperature;//温度
    	private float humidity;//湿度
    	private float pressure;//气压
    	
    	public WeatherData(){
    		observers = new ArrayList<Observer>();
    	}
    	
    	@Override
    	public void registerObserver(Observer o) {
    		observers.add(o);
    	}
    
    	@Override
    	public void removeObserver(Observer o) {
    		observers.remove(0);
    	}
    
    	@Override
    	public void notifyObservers() {
    		for(Observer o : observers){
    			//推送给观察者们
    			o.update(temperature, humidity, pressure);
    		}
    	}
    	
    	//检测改变
    	public void measurementsChanged(){
    		notifyObservers();
    	}
    
    	//也可以让观察者自己来取
    	public ArrayList<Observer> getObservers() {
    		return observers;
    	}
    
    	//也可以让观察者自己来取
    	public float getTemperature() {
    		return temperature;
    	}
    
    	//也可以让观察者自己来取
    	public float getPressure() {
    		return pressure;
    	}
    	
    	public void setMeasurements(float temperature, float humidity, float pressure){
    		this.temperature = temperature;
    		this.humidity = humidity;
    		this.pressure = pressure;
    		measurementsChanged();
    	}
    
    }

package observer;
    
    public class CurrentConditionsDisplay implements Observer, DisplayElement{
    	private float temperature;//温度
    	private float humidity;//湿度
    	private float pressure;//气压
    	private Subject weatherData;
    	
    	public CurrentConditionsDisplay(Subject weatherData){
    		this.weatherData = weatherData;
    		weatherData.registerObserver(this);
    	}
    
    	@Override
    	public void update(float temp, float humidity, float pressure) {
    		this.temperature = temp;
    		this.humidity = humidity;
    		this.pressure = pressure;
    		this.display();
    	}
    
    	@Override
    	public void display() {
    		System.out.println("Current conditions:"+temperature +"#" + humidity +"#"+ pressure);
    	}
    }

package observer;
    
    /**
     * 气象站
     */
    public class WeatherStation {
    	public static void main(String[] args) {
    		WeatherData weatherData = new WeatherData();
    		
    		CurrentConditionsDisplay currentDisplay = new CurrentConditionsDisplay(weatherData);
    		
    		weatherData.setMeasurements(80, 65, 78);
    		weatherData.setMeasurements(11, 111, 1111);
    		weatherData.setMeasurements(22, 222, 222);
    		
    	}
    	/**
    	 * 运行结果：
    	 *  Current conditions:80.0#65.0#78.0
    		Current conditions:11.0#111.0#1111.0
    		Current conditions:22.0#222.0#222.0
    	 */
    }

java也有内置的观察者模式，但是这边是使用观察者去拉数据的方式，而不是把数据推给观察者

源代码很少，可以去翻阅查询，在java.util包下面

1、代码结构：

![SouthEast 1][]

package observer1;
    
    /**
     * 布告板
     */
    public interface DisplayElement {
    
    	/**
    	 * 当布告板需要显示时，调用此方法
    	 */
    	public void display();
    }

package observer1;
    
    import java.util.Observable;
    
    /**
     * 天气数据，继承了‘可观察者’类
     */
    public class WeatherData extends Observable{
    
    	private float temperature;//温度
    	private float humidity;//湿度
    	private float pressure;//气压
    	
    	//检测改变
    	public void measurementsChanged(){
    		setChanged();//设置已经改变，这样的手动设置可以控制信息的手动推送
    		notifyObservers();
    	}
    	
    	public void setMeasurements(float temperature, float humidity, float pressure){
    		this.temperature = temperature;
    		this.humidity = humidity;
    		this.pressure = pressure;
    		measurementsChanged();
    	}
    
    	//也可以让观察者自己来取
    	public float getTemperature() {
    		return temperature;
    	}
    
    	//也可以让观察者自己来取
    	public float getPressure() {
    		return pressure;
    	}
    
    	//也可以让观察者自己来取
    	public float getHumidity() {
    		return humidity;
    	}
    }

package observer1;
    
    import java.util.Observable;
    import java.util.Observer;
    
    /**
     * 显示当前的气象信息
     */
    public class CurrentConditionsDisplay implements Observer,DisplayElement{
    	Observable observable;//可观察者
    	private float temperature;//温度
    	private float humidity;//湿度
    	private float pressure;//气压
    
    	public CurrentConditionsDisplay(Observable observable){
    		this.observable = observable;
    		observable.addObserver(this);
    	}
    	
    	@Override
    	public void update(Observable o, Object arg) {
    		if(o instanceof WeatherData){
    			WeatherData weatherData = (WeatherData) o;
    			//从气象数据中进行取得数据
    			this.temperature = weatherData.getTemperature();
    			this.humidity = weatherData.getHumidity();
    			this.pressure = weatherData.getPressure();
    			display();
    		}
    	}
    
    	@Override
    	public void display() {
    		System.out.println("Current conditions:"+temperature +"#" + humidity +"#"+ pressure);
    	}
    }

package observer1;
    
    /**
     * 气象站
     */
    public class WeatherStation {
    	public static void main(String[] args) {
    		WeatherData weatherData = new WeatherData();
    		
    		CurrentConditionsDisplay currentDisplay = new CurrentConditionsDisplay(weatherData);
    		
    		weatherData.setMeasurements(80, 65, 78);
    		weatherData.setMeasurements(11, 111, 1111);
    		weatherData.setMeasurements(22, 222, 222);
    		
    	}
    	/**
    	 * 运行结果：
    	 *  Current conditions:80.0#65.0#78.0
    		Current conditions:11.0#111.0#1111.0
    		Current conditions:22.0#222.0#222.0
    	 */
    }

[SouthEast]: /images/20230601/1cd306e563ec4ab9a20d7fc30bd865e1.png
[SouthEast 1]: /images/20230601/2aa28170d670417b9c7201dfb7f9079c.png