I've tried to make my actor class observable (extends Actor with Observable[T]). However, there is an error message that I have to implement the asJavaObserver value but there is no asJavaObserver in observable trait.
Aren't you mixing two separate programming paradigms? Actors only communicate by messages. So if anyone is interested in the state change of an actor it must receive a message from the actor.
The observable stuff is for other OO programs which don't use Actor model.