题目

气象局需要我们构建一套系统，这系统有两个公告牌，分别用于显示当前的实时天气和未来几天的天气预报。当气象局发布新的天气数据（WeatherData）后，两个公告牌上显示的天气数据必须实时更新。气象局同时要求我们保证程序拥有足够的可扩展性，因为后期随时可能要新增新的公告牌。

概况

这套系统中主要包括三个部分：气象站（获取天气数据的物理设备）、WeatherData（追踪来自气象站的数据，并更新公告牌）、公告牌（用于展示天气数据）

WeatherData知道如何跟气象站联系，以获得天气数据。当天气数据有更新时，WeatherData会更新两个公告牌用于展示新的天气数据。

结构

/** * 主题 * */public interface Subject {		/**	 * 注册观察者	 * */	void registerObserver(Observer obserber);	/**	 * 移除观察者	 **/	void removeObserber(Observer obserber );	/**	 * 通知	 * */	void notifyObserbers();

public class WeatherData implements Subject {	private List
    
      obserbers;	private float temperature; // 温度	private float pressure; // 气压	private List
     
       forecastTemperatures; // 未来几天的温度	public WeatherData() {		this.obserbers = new ArrayList
      
       ();	}	@Override	public void registerObserver(Observer obserber) {		obserbers.add(obserber);	}	@Override	public void removeObserber(Observer obserber) {		obserbers.remove(obserber);	}	@Override	public void notifyObserbers() {		Iterator
       
         iterator = obserbers.iterator();		while (iterator.hasNext()) {			Observer observer = iterator.next();			observer.update();		}	}	public void measurementsChanged() {		notifyObserbers();	}	public void setMeasurements(float temperature, float pressure, List
        
          forecastTemperatures) {		this.temperature = temperature;		this.pressure = pressure;		this.forecastTemperatures = forecastTemperatures;		measurementsChanged();	}	public List
         
           getObserbers() { return obserbers; } public void setObserbers(List
          
            obserbers) { this.obserbers = obserbers; } public float getTemperature() { return temperature; } public void setTemperature(float temperature) { this.temperature = temperature; } public float getPressure() { return pressure; } public void setPressure(float pressure) { this.pressure = pressure; } public List
           
             getForecastTemperatures() { return forecastTemperatures; } public void setForecastTemperatures(List
            
              forecastTemperatures) { this.forecastTemperatures = forecastTemperatures; }}
            
           
          
         
        
       
      
     
    

/** * 观察者 * */public interface Observer {	/**	 * 更新	 * */	void update();}

/** * 公告牌 * */public interface DisplayElement {	/**	 *展示	 * */	public void display();	}

public class CurrentConditionsDisplay implements Observer , DisplayElement {	private WeatherData weatherData ;	private float temperature ; //湿度	private float pressure; // 气压			public CurrentConditionsDisplay (WeatherData weatherData ) {		this.weatherData = weatherData ; 		this.weatherData.registerObserver(this);	}		@Override	public void update() {		this.temperature = this.weatherData.getTemperature();		this.pressure = this.weatherData.getPressure();		display();	}	@Override	public void display() {		System.out.println("当前湿度：" + this.temperature );		System.out.println("当前气压：" + this.pressure );	}}

public class ForecastDisplay implements Observer, DisplayElement {	private WeatherData weatherData  ;	private List
    
      forecastTemperatures ; 		public ForecastDisplay(WeatherData weatherData) {		this.weatherData = weatherData ;		this.weatherData.registerObserver(this);	}		@Override	public void display() {		System.out.println("未来几天气温：");		int count = forecastTemperatures.size() ;		for(int i = 0 ; i < count ; i++) {			System.out.println("第"+ i + "天，气温：" + forecastTemperatures.get(i) + "℃");		}	}	@Override	public void update() {		this.forecastTemperatures = weatherData.getForecastTemperatures() ;		display();	}}
    

测试类

public class Test {	public static void main(String[] args) {		List
    
      forecastTemperatures = new ArrayList<>();		forecastTemperatures.add((float) 28);		forecastTemperatures.add((float) 32);		forecastTemperatures.add((float) 30);		WeatherData whatherData = new WeatherData();		whatherData.setTemperature(32);		whatherData.setPressure(15);		whatherData.setForecastTemperatures(forecastTemperatures);		CurrentConditionsDisplay currentConditionsDisplay = new CurrentConditionsDisplay(whatherData);		ForecastDisplay forecastDisplay = new ForecastDisplay(whatherData);		System.out.println("-------whatherData初始化-------");		currentConditionsDisplay.update();		forecastDisplay.update();		System.out.println("-------whatherData数据更改-------");		forecastTemperatures.clear();		forecastTemperatures.add((float) 29);		forecastTemperatures.add((float) 33);		forecastTemperatures.add((float) 31);		whatherData.setMeasurements(33, 16, forecastTemperatures);			}}
    

运行结果：

-------whatherData初始化-------当前湿度：32.0当前气压：15.0未来几天气温：第0天，气温：28.0℃第1天，气温：32.0℃第2天，气温：30.0℃-------whatherData数据更改-------当前湿度：33.0当前气压：16.0未来几天气温：第0天，气温：29.0℃第1天，气温：33.0℃第2天，气温：31.0℃