Defining, creating, and messaging actors

The actors are defined as classes that inherit from the Actor class from the Akka library:

class HelloWorld extends Actor {

Actor exposes the following abstract API:

The only method that is abstract in Actor is the receive method. Akka calls this method when an actor needs to handle an incoming message. It returns a partial function from Any to Unit. This means that it is capable of handling a message from a domain of all objects, and it is supposed to produce some side effects while handling this message, which is indicated by the Unit return type. That function is a partial function, which means that it can handle only a part of the input Any domain that your actor is interested in.

When your define an actor, you override this method to define what the actor must do:

val log = Logging(context.system, this)

def receive = {
  case Ping ⇒ log.info("Hello World")
}

The message is defined as follows:

case object Ping

So, when an actor receives the ping message...