設計模式 - 觀察者模式(Observer Pattern) Java內置 使用方法

觀察者模式(Observer Pattern) Java內置 使用方法

本文地址: http://blog.csdn.net/caroline_wendy/article/details/26601659

觀察者模式(observer pattern)詳解, 參見: http://blog.csdn.net/caroline_wendy/article/details/26583157

Java內置的觀察者模式, 是通過繼承父類, 實現觀察者模式的幾個主要函數:

Observerable(可被觀察的): 是一個父類(class),addObserver(), 添加觀察者; deleteObserver(), 刪除觀察者; 

notifyObservers(), 通知觀察者;setChanged(), 確認更改;

Observer(觀察者): 是一個接口(interface), update(), 更新觀察者數據;

setChanged()->notifyObservers(), 必須要先使用setChanged(), 再使用notifyObservers(),  即先確認提交, 再通知觀察者;

觀察者的更新接口update(Observerable o, Object arg), 即可以使用推(push), 也可以使用拉(pull);

如果notifyObservers(arg), 傳遞參數, 則爲推(push)的方法, 如果沒有參數, 則爲拉(pull)的方式, 即使用get()方法獲取;

觀察者的通知(notify)順序是先入後出的模式.

Observerable(可被觀察的) 的 代碼:

/**
 * @time 2014年5月22日
 */
package observer.java;

import java.util.Observable;

/**
 * @author C.L.Wang
 *
 */
public class WeatherData extends Observable {
    private float temperature;
    private float humidity;
    private float pressure;

    public WeatherData() {}

    public void measurementsChanged() {
        setChanged();
        notifyObservers();
    }

    public void setMeasurements(float temperature, float humidity, float pressure) {
        this.temperature = temperature;
        this.humidity = humidity;
        this.pressure = pressure;
        measurementsChanged();
    }

    public float getTemperature() {
        return temperature;
    }

    public float getHumidity() {
        return humidity;
    }

    public float getPressure() {
        return pressure;
    }
}

/**
 * @time 2014年5月22日
 */
package observer.java;

import java.util.Observable;

/**
 * @author C.L.Wang
 *
 */
public class WeatherData extends Observable {
	private float temperature;
	private float humidity;
	private float pressure;
	
	public WeatherData() {}
	
	public void measurementsChanged() {
		setChanged();
		notifyObservers();
	}
	
	public void setMeasurements(float temperature, float humidity, float pressure) {
		this.temperature = temperature;
		this.humidity = humidity;
		this.pressure = pressure;
		measurementsChanged();
	}
	
	public float getTemperature() {
		return temperature;
	}
	
	public float getHumidity() {
		return humidity;
	}
	
	public float getPressure() {
		return pressure;
	}
}

Observer(觀察者)的代碼:

/**
 * @time 2014年5月22日
 */
package observer.java;

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

/**
 * @author C.L.Wang
 *
 */
public class CurrentConditionsDisplay implements Observer, DisplayElement {

    Observable observable;
    private float temperature;
    private float humidity;

    public CurrentConditionsDisplay(Observable observable) {
        this.observable = observable;
        observable.addObserver(this);
    }

    /* (non-Javadoc)
     * @see observer.java.DisplayElement#display()
     */
    @Override
    public void display() {
        // TODO Auto-generated method stub
        System.out.println("Current conditions: " + temperature +
                "F degrees and " + humidity + "% humidity");
    }

    /* (non-Javadoc)
     * @see java.util.Observer#update(java.util.Observable, java.lang.Object)
     */
    @Override
    public void update(Observable o, Object arg) {
        // TODO Auto-generated method stub
        if (o instanceof WeatherData) {
            WeatherData weatherData = (WeatherData)o;
            this.temperature = weatherData.getTemperature();
            this.humidity = weatherData.getHumidity();
            display();
        }
    }

}

/**
 * @time 2014年5月22日
 */
package observer.java;

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

/**
 * @author C.L.Wang
 *
 */
public class CurrentConditionsDisplay implements Observer, DisplayElement {

	Observable observable;
	private float temperature;
	private float humidity;
	
	public CurrentConditionsDisplay(Observable observable) {
		this.observable = observable;
		observable.addObserver(this);
	}
	
	/* (non-Javadoc)
	 * @see observer.java.DisplayElement#display()
	 */
	@Override
	public void display() {
		// TODO Auto-generated method stub
		System.out.println("Current conditions: " + temperature + 
				"F degrees and " + humidity + "% humidity");
	}

	/* (non-Javadoc)
	 * @see java.util.Observer#update(java.util.Observable, java.lang.Object)
	 */
	@Override
	public void update(Observable o, Object arg) {
		// TODO Auto-generated method stub
		if (o instanceof WeatherData) {
			WeatherData weatherData = (WeatherData)o;
			this.temperature = weatherData.getTemperature();
			this.humidity = weatherData.getHumidity();
			display();
		}
	}

}

其餘代碼不一一列出, 類似參見: http://blog.csdn.net/caroline_wendy/article/details/26583157

測試代碼:

package observer.java;

public class WeatherStation {

    public static void main(String[] args) {
        WeatherData weatherData = new WeatherData();
        CurrentConditionsDisplay currentConditions = new CurrentConditionsDisplay(weatherData);
        StatisticsDisplay statisticsDisplay = new StatisticsDisplay(weatherData);
        ForecastDisplay forecastDisplay = new ForecastDisplay(weatherData);

        weatherData.setMeasurements(80, 65, 30.4f);
        weatherData.setMeasurements(82, 70, 29.2f);
        weatherData.setMeasurements(78, 90, 29.2f);
    }
}

package observer.java;

public class WeatherStation {

	public static void main(String[] args) {
		WeatherData weatherData = new WeatherData();
		CurrentConditionsDisplay currentConditions = new CurrentConditionsDisplay(weatherData);
		StatisticsDisplay statisticsDisplay = new StatisticsDisplay(weatherData);
		ForecastDisplay forecastDisplay = new ForecastDisplay(weatherData);

		weatherData.setMeasurements(80, 65, 30.4f);
		weatherData.setMeasurements(82, 70, 29.2f);
		weatherData.setMeasurements(78, 90, 29.2f);
	}
}

輸出:

Forecast: Improving weather on the way!
Avg/Max/Min temperature = 80.0/80.0/80.0
Current conditions: 80.0F degrees and 65.0% humidity
Forecast: Watch out for cooler, rainy weather
Avg/Max/Min temperature = 81.0/82.0/80.0
Current conditions: 82.0F degrees and 70.0% humidity
Forecast: More of the same
Avg/Max/Min temperature = 80.0/82.0/78.0
Current conditions: 78.0F degrees and 90.0% humidity