A class can implement the Observer interface when it
wants to be informed of changes in observable objects.
public interface interface FWObserver { // Public Instance Methods
public void update(FWObservable aFormObservable, Object aArg);
This method is called whenever the observed object is changed. An
application calls an Observable object's
notifyObservers method to have all the object's
observers notified of the change.
aFormObservable the observable object.
aArg an argument passed to the notifyObservers
method.