将Akka Iterable转换为java.lang.Iterable吗？

Question

I would like to iterate over the children of a given Actor in a for-each loop, like so:

    for(ActorRef child: this.getContext().children()){
      // do things
    }

This yields an error though:

    HelloWorld.java:78: error: for-each not applicable to expression type
                    for(ActorRef child: this.getContext().children())
                                                                  ^
      required: array or java.lang.Iterable
      found:    Iterable<ActorRef>
    1 error

The docs for UntypedActorContext say that the children() method should return an ' Iterable[ActorRef] ', but the inline-hyperlink for the type definition for that particular ' Iterable ' leads to the docs for the Scala Iterable-type rather than the Java type, which are not the same thing.

This can be confirmed in practice: the object returned from the children() call fails an "instanceOf Iterable" check, and calling " getClass() " on it returns "class akka.actor.dungeon.ChildrenContainer$ChildrenIterable ".

It seems pretty clear to me that this is not a Java Iterable and that the error is appropriate. But how do I coerce or marshall it into a Java Iterable? This link in the Scala docs suggests that there are conversion functions for Scala->Java, but I cannot make heads or tails of what to import or how to call them from Java; the only examples I've seen have been for Scala.

PS I realize I can probably use a while-loop and the Scala-Iterator returned by children().iterator() to construct the equivalent of a for-each loop here. What I'm really after is understanding how to use the type-conversion routines that Scala provides.

Answer 1

I haven't used Scala, but the doc is saying

java.lang.Iterable<ActorRef> jChildren = JavaConversions.asJavaIterable (this.getContext().children());
for (ActorRef child: jChildren) {
    // do stuff
}

Note: if both types of Iterables are used in the same class you need to expand java.lang.Iterable in the declaration to make sure it uses the right one.

Alternately you could do in one line as such:

for (ActorRef child: JavaConversions.asJavaIterable(this.getContext().children())) {
    // do stuff
}

Answer 2

If you're using Java, you would be using UntypedActor and its UntypedActorContext, which provides a getChildren() -method: http://doc.akka.io/japi/akka/2.3.4/akka/actor/UntypedActorContext.html

Doc:

java.lang.Iterable<ActorRef>    getChildren() 
      Returns an unmodifiable Java Collection containing the linked actors, please note that the backing map is thread-safe but not immutable