Server source code.

Server.scala

import akka.actor._

object Server extends App {
  val system = ActorSystem("serverSystem")
  val serverActor = system.actorOf(Props(new ServerActor), name = "ServerActor")
}

class ServerActor extends Actor {
  def receive = {
    case message: String =>
      println("Internal monologue: What? Someone said hello. Nobody taught me any social skills in this basement. I should say hi back.")
      sender ! "Hi."
    case _ => println("I got something I didn't understand.")
  }
}