I simply want to know the actor of the
Terminated terminated = (Terminated)message;
terminated.actor(); // what is this?
terminated.getActor(); // what is that?
There is no difference.
actor is simply the Scala property, whereas
getActor is the corresponding Java accessor.
You can see it in the signature of the class:
final case class Terminated private[akka] (@BeanProperty actor: ActorRef)
@BeanProperty annotation is a special Scala one that generates accessors and mutators (
setX) for Java bean compatibility.