观察者模式

观察者模式：定义了对象之间的一对多依赖，这样一来，当一个对象改变状态时，他的所有依赖者都会受到通知并自动更新。

具体内容见：Head First设计模式

气象站模型：气象站提供气象数据，布告板显示。

定义观察者接口
public interface Observer {
	public void update(float temp,float humi,float pressure);
}
定义主题接口
public interface Subject {
	public void registerObserver(Observer o);
	public void removeObserver(Observer o);
	public void notifyObservers();
}
定义显示装置接口
public interface DisplayElement {
	public void display();
}
具体主题
public class WeatherData implements Subject {
	private ArrayList<Observer> observers;
	private float temperature;
	private float humidity;
	private float pressure;

	/**
	 * 
	 */
	public WeatherData() {
		observers = new ArrayList<Observer>();
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see com.zen.dp.observer.Subject#notifyObservers()
	 */
	@Override
	public void notifyObservers() {
		for (Observer o : observers) {
			o.update(temperature, humidity, pressure);
		}
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see
	 * com.zen.dp.observer.Subject#registerObserver(com.zen.dp.observer.Observer
	 * )
	 */
	@Override
	public void registerObserver(Observer o) {
		observers.add(o);
	}

	/*
	 * (non-Javadoc)
	 * 
	 * @see
	 * com.zen.dp.observer.Subject#removeObserver(com.zen.dp.observer.Observer)
	 */
	@Override
	public void removeObserver(Observer o) {
		int i = observers.indexOf(o);
		if (i >= 0)
			observers.remove(i);
	}

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

}
具体观察者及显示装置
public class TVDisplay implements Observer, DisplayElement {
	private float temperature;
	private float humidity;
	private Subject weatherData;
	
	/**
	 * 
	 */
	public TVDisplay(Subject wd) {
		this.weatherData = wd;
		wd.registerObserver(this);
	}
	/* (non-Javadoc)
	 * @see com.zen.dp.observer.Observer#update(float, float, float)
	 */
	@Override
	public void update(float temp, float humi, float pressure) {
		this.temperature=temp;
		this.humidity=humi;
		display();
	}

	/* (non-Javadoc)
	 * @see com.zen.dp.observer.DisplayElement#display()
	 */
	@Override
	public void display() {
		System.out.println("当前的气象条件是：温度为"+temperature+"摄氏度,湿度为"+humidity+"%");
	}

}
气象站
public class WeatherStation {
	public static void main(String[] args) {
		WeatherData wd = new WeatherData();
		TVDisplay tvdisplay = new TVDisplay(wd);
		wd.setMeasurements(18, 46, 30);
		wd.setMeasurements(20, 30, 28);
	}
}