Java设计模式 -- 观察者模式(pull方式)

还是和push一样，有个主题WeatherData.java的类

import java.util.Observable;
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;
	}
}

请注意：这里的WeahterData.java继承的是java.util.Observable

在Observable方法中

setChanged();方法把changed设置为true;

notifyObservers();方法只有在changed为true的时候才去通知观察者。

接下来是观察者对象：CurrentConditionsDisplay.java对象。

import java.util.Observable;
import java.util.Observer;
import org.inter.DisplayElement;
public class CurrentConditionsDisplay implements Observer, DisplayElement{
	Observable observable;
	private float temperature;
	private float humidity;
	public CurrentConditionsDisplay(Observable observable)
	{
		this.observable = observable;
		observable.addObserver(this);
	}
	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();
		}
	}
	public void display() {
		// TODO Auto-generated method stub
		System.out.println(temperature + " : " + humidity);
	}
}

同push同样的方法来验证：

public class PushWeatherStation {
	public static void main(String[] args)
	{
		WeatherData wd = new WeatherData();
		CurrentConditionsDisplay display = new CurrentConditionsDisplay(wd);
		wd.setMeasurements(80, 65, 30.4f);
		wd.setMeasurements(10, 25, 30.4f);
	}
	
}

评论

1 楼 yzhong_sa 2010-05-11  

能不能简要的说说Observable 与 observer之间的关系，以及他们可以使用的通信方式及区别呢。。学习中 谢了