用Java确定Scala对象的类

Question

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)?

Answer 1

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 ).