Observer Design Pattern

observer-pattern.java

public interface Subject {
    public void registerObserver(Observer o);
    public void removeObserver(Observer o);
    public void notifyObservers();
}

public interface Observer {
    public void update(float temp, float humidity, float pressure);
}

public interface DisplayElement {
    public void display();
}

public class WeatherData implements Subject {
    private ArrayList<Observer> observers;
    private float temp;
    private float humidity;
    private float pressure;

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

    public void registerObserver(Observer o) { observers.add(o); }
    public void removeObserver(Observer o) { observers.remove(o); }
    public void notifyObservers() {
        for (Observer o : observers)
            o.update(temp, humidity, pressure);
    }
    public void mesurementsChanged() { notifyObservers(); }
    public void setMeasurements(float temp, float humidity, float pressure) {
        this.temp = temp;
        this.humidity = humidity;
        this.pressure = pressure;
    }
}

public class CurrentConditionsDisplay implements Observer, DisplayElement {
    private float temp;
    private float humidity;
    private Subject WeatherData;

    public CurrentConditionsDisplay(Subject WeatherData) {
        this.WeatherData = WeatherData;
        WeatherData.removeObserver(this);
    }

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

    public void display() {
        System.out.println("Current conditions: " + temp + "F and " + humidity + "%");
    }
}