public interface Observer {
    /**
     * 通知觀察者變化信息
     *
     * @param temperature
     * @param humidity
     */
    void update(float temperature,float humidity);
}

public interface Subject {
    /**
     * 注冊(cè)觀察者
     *
     * @param observer
     */
    void registerObserver(Observer observer);
    /**
     * 刪除觀察者
     *
     * @param observer
     */
    void removeObserver(Observer observer);
    /**
     * 通知所有觀察者
     */
    void notifyObservers();
}

public class WeatherData implements Subject {
    private List<Observer> observers;
    private float temperature;
    private float humidity;
    public WeatherData() {
        observers = new ArrayList<>();
    }
    /**
     * 注冊(cè)觀察者
     *
     * @param observer
     */
    @Override
    public void registerObserver(Observer observer) {
        observers.add(observer);
    }
    /**
     * 刪除觀察者
     *
     * @param observer
     */
    @Override
    public void removeObserver(Observer observer) {
        observers.remove(observer);
    }
    /**
     * 通知所有觀察者
     */
    @Override
    public void notifyObservers() {
        observers.forEach(observer -> observer.update(temperature, humidity));
    }
    /**
     * 設(shè)置天氣信息
     *
     * @param temperature
     * @param humidity
     */
    public void setMeasurements(float temperature, float humidity) {
        this.temperature = temperature;
        this.humidity = humidity;
        notifyObservers();
    }
}

public class CurrentConditionsDisplay implements Observer {
    private float temperature;
    private float humidity;
    public CurrentConditionsDisplay(Subject weatherData) {
        weatherData.registerObserver(this);
    }
    /**
     * 通知觀察者變化信息
     *
     * @param temperature
     * @param humidity
     */
    @Override
    public void update(float temperature, float humidity) {
        this.temperature = temperature;
        this.humidity = humidity;
        display();
    }
    private void display() {
        System.out.println("溫度:" + temperature + "℃;濕度:" + humidity + "%");
    }
}

public class Demo {
    public static void main(String[] args) {
        WeatherData weatherData = new WeatherData();
        CurrentConditionsDisplay currentConditionsDisplay = new CurrentConditionsDisplay(weatherData);
        weatherData.setMeasurements(35,53);
        weatherData.setMeasurements(32,48);
        weatherData.setMeasurements(26,44);
    }
}