Question

I have the following notification sent for an Observer and Observable design pattern

private void changeEnvironment()
    {
        Random random = new Random();
        season = SEASON[random.nextInt(3)];
        dayInTime = DAY_IN_TIME[random.nextInt(2)];
        temperature = random.nextInt(120);
        setChanged();
        notifyObservers(season);
        notifyObservers(dayInTime);
        notifyObservers(temperature);
    }

However, in my:

public void update(Observable o, Object arg) {

    }

How do I check whether it’s season, dayInTime, or temperature?

Answer 1

You can use the observer pattern in pull mode , which means that observable will pass itself to the observer ‘s update() .So , observer can get properties they want from the observable ‘s getters.

I assume temperature, dayInTime , season in your subject are both int

So , you Observable (i.e Subject) will looks like :

public class Subject extends Observable{

    private int temperature;
    private int dayInTime;
    private int season;

    private void changeEnvironment() {
        Random random = new Random();
        this.season = SEASON[random.nextInt(3)];
        this.dayInTime = DAY_IN_TIME[random.nextInt(2)];
        this.temperature = random.nextInt(120);
        setChanged();

         /** Notify all of the subscribed observers about its changes
          It will call each observers' update(this, null)***/
        notifyObservers();
    }


    public int getTemperature(){....}
    public int getdayInTime(){.....}
    public int getSeason(){....}

}

Then your observer can get temperature, dayInTime , season by using the corresponding getters of your Observable :

public void update(Observable o, Object arg) {

   Subject = (Subject) o;
   int temperature = o.getTemperature();
   int dayInTime= o.getdayInTime();
   int season= o.getSeason();
}