Java设计模式 -- 观察者模式(push方式)

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，它的所有依赖者都会收到通知并自动更新。

当两个对象之间松耦合，他们依然可以交互，但是不太清楚彼此的细节。观察者模式提供了一种对象设计让主题和观察者之间松耦合。

我们来看看一种push方式的 观察者模式。

首先是观察者 主题 等的接口。

//主题
public interface Subject {
	public void registerObserver(Observer o);
	public void removeObserver(Observer o);
	public void notifyObservers();
}
//观察者
public interface Observer {
	
	public void update(float temp, float humidity, float pressure);
}
//other 操作
public interface DisplayElement {
	
	public void display();
}

实现这些接口。

//实现主题
public class WeatherData implements Subject{
	private ArrayList observers;
	private float temperature;
	private float humidity;
	private float pressure;
	
	public WeatherData()
	{
		observers = new ArrayList();
	}
	
	public void notifyObservers() {
		// TODO Auto-generated method stub
		for(int i=0, len=observers.size(); i < len; i++)
		{
			Observer observer = (Observer) observers.get(i);
			observer.update(temperature, humidity, pressure	);
		}
	}
	public void registerObserver(Observer o) {
		// TODO Auto-generated method stub
		observers.add(o);
	}
	public void removeObserver(Observer o) {
		// TODO Auto-generated method stub
		int i = observers.indexOf(o);
		if(i >= 0)
		{
			observers.remove(i);
		}
	}
	
	public void measurementsChange()
	{
		notifyObservers();
	}
	
	public void setMeasurements(float temperature, float humidity, float pressure)
	{
		this.temperature = temperature;
		this.humidity = humidity;
		this.pressure = pressure;
		measurementsChange();
	}
}
//实现观察者
public class CurrentConditionsDisplay implements Observer, DisplayElement{
	private float temperature;
	private float humidity;
	private Subject weatherData;
	
	public CurrentConditionsDisplay(Subject weatherData)
	{
		this.weatherData = weatherData;
		weatherData.registerObserver(this);
	}
	
	public void update(float temp, float humidity, float pressure) {
		// TODO Auto-generated method stub
		this.temperature = temp;
		this.humidity = humidity;
		display();
	}
	public void display() {
		// TODO Auto-generated method stub
		System.out.println("Current conditions: "+ temperature + "F degrees and " + humidity + "% humidity");
	}
}

实现完了这些接口，测试观察者模式

public class WeatherStation {
	public static void main(String[] args)
	{
		WeatherData weatherData = new WeatherData();
		
		CurrentConditionsDisplay display = new CurrentConditionsDisplay(weatherData);
		
		weatherData.setMeasurements(80, 65, 30.4f);
		weatherData.setMeasurements(82, 76, 30.2f);
		weatherData.setMeasurements(78, 90, 29.4f);
	}
}