How to create a scala.collection.immutable.Seq from a Java List in Java?

Question

I'm trying to get Akka going in my Java project, and I'm hung up on a small issue with the Seq type(s) from Scala. I'm able to convert my Java List of ActorRef into a scala.collection.Seq, but the Akka API I'm trying to use requires a scala.collection.immutable.Seq. How can I make one?

Code:

static class Router extends UntypedLoadBalancer {
    private final InfiniteIterator<ActorRef> workers;

    public Router(List<ActorRef> workers) {
        Seq workerSeq = asScalaBuffer(workers);

        // how to get from the scala.collection.Seq above to the instance of
        // scala.collection.immutable.Seq required by CyclicIterator below?
        this.workers = new CyclicIterator<ActorRef>();
    }

    public InfiniteIterator<ActorRef> seq() {
        return workers;
    }
}

Landei · Accepted Answer · 2011-07-22T07:17:44.113

47

You can use scala.collection.JavaConversions.asScalaBuffer to convert the Java List to a Scala Buffer, which has a toList method, and a Scala List is a collection.immutable.Seq.

edited Jul 22 '11 at 07:17

answered Jul 22 '11 at 06:50

Landei

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Picked this one as it answered my specific question more closely. The line I ended up with was: new CyclicIterator((Seq) asScalaBuffer(workers).toList()); – spieden Jul 22 '11 at 17:42

score 4 · Answer 2 · answered Jul 22 '11 at 02:25

4

The akka Java documentation for routers as well as the ScalaDoc for CyclicIterator both suggest that the CyclicIterator constructor takes a List.

answered Jul 22 '11 at 02:25

Emil Sit

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Thanks for the answer. I guess I was mistaking immutable.Seq for a concrete type! – spieden Jul 22 '11 at 17:41

score 3 · Answer 3 · edited Nov 07 '19 at 07:51

3

You can try this:

scala.collection.JavaConverters.asScalaIteratorConverter(list.iterator()).asScala().toSeq();

edited Nov 07 '19 at 07:51

Dino

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answered Nov 06 '19 at 20:33

markus

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score 1 · Answer 4 · answered Mar 12 '17 at 08:19

1

You can use:

scala.collection.JavaConverters.collectionAsScalaIterableConverter(workers).asScala().toSeq()

answered Mar 12 '17 at 08:19

Ben McCann

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score 0 · Answer 5 · answered Nov 05 '22 at 18:45

Since scala 2.12.0 JavaConversions is marked deprecated

@deprecated("use JavaConverters", since="2.12.0")
object JavaConversions extends WrapAsScala with WrapAsJava

so one should use JavaConverters

scala.collection.JavaConverters.asScalaIteratorConverter(list.iterator()).asScala().toSeq();

or idiomatically

scala.collection.JavaConverters.asScalaIterator(list.iterator()).toSeq();

How to create a scala.collection.immutable.Seq from a Java List in Java?

5 Answers5

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