Java - block in a constructor method call

Question

// allows passing in arguments to the MyActor constructor
ActorRef myActor = system.actorOf(new Props(new UntypedActorFactory() 
  {                                  // 
    public UntypedActor create() {   //
      return new MyActor("...");     //   <- this part confuses me
    }                                //
  }                                  //
 ), "myactor");

I am new to Java, going through the Akka documentation. and I find the above code confusing. Especially the code block below. How can a block of code be sent to the "new UntypedActorFactory()" constructor call. What is this type of constructor initialization called.

{
public UntypedActor create() {
return new MyActor("...");
}

Answer 1

The part that confused you creates an anonymous class, then instantiates it, and passes the newly created instance to a method as an argument. The block of code you are referring to is the body of anonymous class that is derived from UntypedActorFactory

For instance, if you have an interface:

interface SomeInterface {
    void someMethod();
}

You can create an anonymous class that implements your interface like this (similar syntax is suitable for extending named classes):

SomeInterface instance = new SomeInterface() {
    public void someMethod() {    //
        // implementation here    //  <- similar to the example, 
    }                             //     this is the body of anonymous class
};                                //

Answer 2

This is an anonymous class.

This is simply a new class inheriting from UntypedActorFactory with the declared method.