Java observer pattern for a GUI - distinguish between different events without typeof

I have a simple Controller object that that implements Observer (i.e. it is the observer) which listens for events from a Mouse object that extends Observable (i.e. it is the observee).

So there can be multiple events in a Mouse object e.g. left click, scroll up, etc.

Now the Controller class implements the required method which is called every time any of the above events happen:

@Override
public void update(Observable o, Object arg)
{

}

So it is the arg parameter that I am having trouble deciding how to approach (this case I am working on is simple enough such that the o parameter is not a concern). What is a good way to distinguish between different mouse events without using typeof?

I.e. what parameter should I feed in the notifyObservers(Object arg) method in the Mouse observee class?