观察者模式

public interface Observer {

    void update(float temperature, float humidity, float pressure);
}

主体;

public interface Subject {

    public void registerObserver(Observer observer);

    public void removeObserver(Observer observer);

    public void notifyObserver();


}

变更的数据：

public class WeatherData implements Subject{

    private List<Observer> observers;
    private float temperature;
    private float humidity;
    private float pressure;

    public WeatherData() {
        this.observers = new ArrayList<>();
    }

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

    @Override
    public void registerObserver(Observer observer) {
        observers.add(observer);
    }

    @Override
    public void removeObserver(Observer observer) {
        int i = observers.indexOf(observer);
        if (i >= 0){
            observers.remove(observer);
        }
    }
    @Override
    public void notifyObserver() {
        for (Observer o : observers) {
            o.update(temperature,humidity,pressure);
        }
    }


}

被观察者1：

public class CurrentConditionsDisplay implements Observer{

    public CurrentConditionsDisplay(Subject weatherData) {
        weatherData.registerObserver(this);
    }

    @Override
    public void update(float temperature, float humidity, float pressure) {
        System.out.println("CurrentConditionsDisplay update:"+temperature+" "+humidity+" "+pressure);
    }
}

被观察者2：

public class StatisticsDisplay implements Observer{

    /**
     * 订阅天气数据
     * @param weatherData
     */
    public StatisticsDisplay(Subject weatherData){
        weatherData.registerObserver(this);
    }

    public void update(float temp, float humidity, float pressure){
        System.out.println("StatisticsDisplay update:"+temp+" "+humidity+" "+pressure);
    }


}