Client source code.

Client.scala

import akka.actor._

object Client extends App {
  val system = ActorSystem("clientSystem")
  val clientActor = system.actorOf(Props(new ClientActor), name = "ClientActor")

  clientActor ! SayHello
}

class ClientActor extends Actor {
  private val server = context.actorSelection("akka.tcp://serverSystem@127.0.0.1:2552/user/ServerActor")

  def receive = {
    case SayHello => server ! "Hello."
    case message: String => println("Client received reply: " + message)
    case _ => println("I got something I didn't understand.")
  }
}

case object SayHello