Movement and Control

That doesn't really make sense - perhaps you meant, control the actors from the world rather than the Actor class? The answer is: if you're worrying about efficiency, you're doing it wrong. Get your code working first. In general, it would be better from a design standpoint to have the logic for an actor in the actor's own class. It makes adding new actor types much easier. You also avoid having to keep lists of different types of actor in your world (or using "instanceof" to determine the actor type, urgh).