Whenever the MailBox component has a message to process, it will invoke the receive method of Actor.

Let's demonstrate how to create various actor-model components and use them by creating a WelCome to Akka application with the help of the following steps:

1. Download akka-actor_2.10.jar and scala-library-2.10.3.jar.
2. Create DemoAkka as a Java Project and add the JARs as external dependencies.
3. Create a POJO MyMessage in the com.packt.ch11.beans package, as shown in the following piece of code:

public class MyMessage implements Serializable 
{ 
  private String message; 
 
  public MyMessage(String message) 
  { 
    this.message = message; 
  } 
  //getters and setters 
} 

4. Create an Actor1 class in the com.packt.ch11.actors package that will implement UntypedActor.
5. Override the onReceive() method as follows:

public class Actor1 extends UntypedActor { 
  public void onReceive(Object message) { 
    if (message instanceof MyMessage) { 
      System.out.println("The message is:" 
          + ((MyMessage) message).getMessage()); 
    } 
  } 
} 

The onReceive() method will be invoked by the Actor1 MailBox whenever MessageDispatcher makes a thread available and there is a message waiting in MessageQueue of MailBox.

6. Create TestAkka with the main() function to test the code.
7. Create a reference for ActorSystem with PacktSystem as its name.
8. Create ActorRef that will point to Actor1.
9. Send a message to ActorRef by invoking the tell method.
10. Finally, shut down ActorSystem as follows:

public static void main(String[] args) { 
  ActorSystem actorSystem =  
    ActorSystem.create("PacktSystem"); 
  ActorRef actorRef = actorSystem.actorOf(new 
     Props(Actor1.class), 
    "actor1"); 
  actorRef.tell(new MyMessage("Hello Welcome to Akka!")); 
 
  try { 
    Thread.sleep(3000); 
  } catch (Exception e) { 
  } 
 
  actorSystem.stop(actorRef); 
  actorSystem.shutdown(); 
} 

11. Execute the code and enjoy the output.

This is just an introductory demo to understand the difference in handling concurrency in OOPs and with Akka.