设计模式

观察者模式(Observer Pattern) Java内置 用法

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

观察者模式(observer pattern)具体解释, 參见: http://blog.csdn.net/caroline_wendy/article/details/26583157

Java内置的观察者模式, 是通过继承父类, 实现观察者模式的几个主要函数:

Observerable(可被观察的): 是一个父类(class),addObserver(), 加入观察者; deleteObserver(), 删除观察者; 

notifyObservers(), 通知观察者;setChanged(), 确认更改;

Observer(观察者): 是一个接口(interface), update(), 更新观察者数据;

setChanged()->notifyObservers(), 必需要先使用setChanged(), 再使用notifyObservers(), 即先确认提交, 再通知观察者;

观察者的更新接口update(Observerable o, Object arg), 即能够使用推(push), 也能够使用拉(pull);

假设notifyObservers(arg), 传递參数, 则为推(push)的方法, 假设没有參数, 则为拉(pull)的方式, 即使用get()方法获取;

观察者的通知(notify)顺序是先入后出的模式.

Observerable(可被观察的) 的 代码:

/**
 * @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(观察者)的代码:

/**
 * @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();
		}
	}

}

其余代码不一一列出, 类似參见: http://blog.csdn.net/caroline_wendy/article/details/26583157

測试代码:

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);
	}
}

输出:

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

注意: 通知的顺序是先入后出.