Question

I was having problems with class design until i found out about observable (using observer design pattern) and thus created a small application using it which solved my problem. I was happy and proud that I had used a good principle to sovle a problem.

Now i am about to start my main application and have just read this

Making a JFrame and Observable Object

Why is the poster advised against the use of observable and instead told to use propertychangelistenr? Is there any issues with using observable?

Regards

Answer 1

Observer and Listener pattern are very similar. But Observer has a weakness: all observables are the same. You have to implement the logic that is based on instanceof and cast object to concrete type into Observable.update() method.

Listeners are different. There are a lot of listener types. For example mouse listener, keyboard listener etc. Each one has several callback methods (i.e. keyPressed(), keyReleased() etc). So, you never have to implement the logic that should answer the question “is it my event” into the event handler.

I think that this is why listener model is preferable.