CODEWITHSUNDEEP
javascala
Arya
Arya

Reputation: 3049

Determine Scala-object's class in Java

I want to check if the given object (which may be created in Scala) is instance-of a specific Class (which is a class or an abstract class in Scala) in Java:

public boolean accept(Object object) {
    System.out.println("1: " + object);
    System.out.println("2: " + object.getClass());
    System.out.println("3: " + (object.getClass().getName() + " - " + RepointableActorRef.class.getName()));
    System.out.println("4: " + (object.getClass() == RepointableActorRef.class));
    System.out.println("5: " + (object instanceof RepointableActorRef));
    System.out.println("6: " + (object instanceof ActorRef));
    System.out.println("7: " + ActorRef.class.isAssignableFrom(RepointableActorRef.class));
    System.out.println("8: " + ActorRef.class.isAssignableFrom(object.getClass()));

    return object instanceof ActorRef; // Always returns false
}

In the above code:

ActorRef is a Scala abstract class:

abstract class ActorRef extends java.lang.Comparable[ActorRef] with Serializable

RepointableActorRef is a Scala class:

private[akka] class RepointableActorRef extends ActorRef

And ActorRef is super-class of RepointableActorRef.

When an instance of RepointableActorRef which is provided by Scala code (I can't modify it), passed to accept method, the following output will be printed:

1: class akka.actor.RepointableActorRef
2: class java.lang.Class
3: java.lang.Class - akka.actor.RepointableActorRef
4: false
5: false
6: false
7: true
8: false

So how can i determine a Scala-object's class in Java? Or using instance of correctly (object instanceof ActorRef in the above code)?

Upvotes: 0

Views: 184

Answers (1)

Alexey Romanov
Alexey Romanov

Reputation: 170919

When an instance of RepointableActorRef which is provided by Scala code (I can't modify it), passed to accept method, the following output will be printed:

No, it won't. This output means Scala code didn't return an instance of RepointableActorRef, it returned an instance of Class, and in particular it returned RepointableActorRef.class.

If you want to check whether this instance represents the RepointableActorRef class, you should compare 

RepointableActorRef.class.equals(object)

If you want to check whether it represents a subtype of ActorRef, it should be

ActorRef.class.isAssignableFrom((Class<?>) object)

(probably after a check that you got a Class).

Upvotes: 1

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