Use conditional in their update() method.
There would be no way for selective event delivery.
In other words, it is universal for observers.

Hi Samir,

An alternative to using the java.util.observable class is to roll your
own.  Create your own listener interface for the observers and build
your observable class with methods for adding and removing listeners.
This listener interface could have mutliple notifications i.e.:

notifyActionA
notifyActionB

The observer classes that are interested in these events would have to
implement the listener interface.  However if a class is not interested
in ActionA, it can leave the implementation for that method empty.

The swing classes often use this pattern, for example a JFrame will
accept MouseListeners.  Classes that implement the MouseListener
interface can receive various mouse events (mouseClicked, mouseEntered,
etc.), but can simply ignore mouse events that aren't needed.

Hope that helps, I'm a novice with Java so others may have better
suggestions.

-Gareth

Hello, Samir!

The way I would go about doing what you want is using the Object
parameter of the update(Observable, Object) method:

public void update(Observable o, Object arg) {
    if (arg somethingsomething) {
        //We know it's for Observer no. 1
    }
    else if (arg somethingelse) {
        //It's for Observer no. 2
    }
}

On the other hand, I'm not the best of Java programmers and this may in
fact be a weird solution.

Your English is just fine, don't worry about it. :-)

- Deniz Dogan

How do you determine that one of the observers is not interested ?

If an observer registers, it's to be notified, and it will look at the
observed object to determine what neeeds done. It's not the observed object
than can know what the observer wants to do.