Java 观察者模式

观察者模式：让你的对象知悉现况

出版者+订阅者=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，
它的所有依赖者都会收到通知并自动更新。

关于观察者的一切，主题只知道观察者实现了某个接口。
主题不需要知道观察者的具体类是谁、做了些什么或其他任何细节。

实现气象站：

主题接口：
public interface Subject {
	public void registerObserver(Observer o);
	public void removerObserver(Observer o);
	public void notifyObserver();	
}

观察者接口
public interface Observer {
	public void update(float temp, float humidity, float pressure);
}

气象站接口（具体的主题）
public class WeatherData implements Subject{
	private ArrayList observers;
	private float temperature;
	private float humidity;
	private float pressure;
	
	public WeatherData(){
		observers = new ArrayList();
	}
	
	@Override
	public void registerObserver(Observer o) {
		observers.add(o);		
	}

	@Override
	public void removerObserver(Observer o) {
		int i = observers.indexOf(o);
		if(i >= 0){
			observers.remove(i);
		}
	}

	@Override
	public void notifyObserver() {
		for (int i = 0; i < observers.size(); i++) {
			Observer observer = (Observer) observers.get(i);
			observer.update(temperature, humidity, pressure);
		}		
	}
	
	//当气象站得到更新观测值时，我们通知观察者。
	public void measurementsChanged(){
		notifyObserver();
	}
	
	public void setMeasurements(float temperature, float humidity, float pressure){
		this.temperature = temperature;
		this.humidity = humidity;
		this.pressure = pressure;
		measurementsChanged();
	}
}


public interface DisplayElement {
	public void display();
}

布告板接口（具体的观察者）
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);
	}	
	
	@Override
	public void display() {
		System.out.println("Current conditions : " + temperature
				+ "F degrees and " + humidity + "% humidity");		
	}

	@Override
	public void update(float temperature, float humidity, float pressure) {
		this.temperature = temperature;
		this.humidity = humidity;
		display();		
	}
}

测试类
public class Test {
	public static void main(String[] args) {
		WeatherData wd = new WeatherData();		
		CurrentConditionsDisplay cc = new CurrentConditionsDisplay(wd);
		wd.setMeasurements(80, 65, 30.4f);		
	}
}

利用JDK内置的支持重做气象站
修改气象站类和布告板类如下：
import java.util.Observable;

public class WeatherData extends Observable{	
	private float temperature;
	private float humidity;
	private float pressure;
	
	public WeatherData(){
	}
		
	//当气象站得到更新观测值时，我们通知观察者。
	public void measurementsChanged(){
		//表示状态已经改变
		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;
	}	
}

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

public class CurrentConditionsDisplay implements Observer,DisplayElement{

	Observable observable;	
	private float temperature;
	private float humidity;	
	
	public CurrentConditionsDisplay(Observable observable) {
		this.observable = observable;
		observable.addObserver(this);
	}	
	
	@Override
	public void display() {
		System.out.println("Current conditions : " + temperature
				+ "F degrees and " + humidity + "% humidity");		
	}

	@Override
	public void update(Observable obs, Object arg) {
		if (obs instanceof WeatherData){
			WeatherData weatherData = (WeatherData)obs;
			this.temperature = weatherData.getTemperature();
			this.humidity = weatherData.getTemperature();
			display();
		}		
	}	
}

猜你喜欢