Convert a java collections into a scala one from java

[Edmondo Porcu]

Dear all,
I am trying to call a Scala API from java, so I need to pass a scala collection.

It is clear to me how to do the conversion inside the Scala code, but
how do you them in java? In particularly I am trying to turn a
java.List into a scala List.

Best Regards
Edmondo

[Daniel Sobral]

Well, from Scala you'd do something like this:

scala.collection.immutable.List$.MODULE$.apply(scala.collection.JavaConversions$.MODULE$.collectionAsScalaIterable(myJavaList).toSeq:
_*)

You might need to sprinkle some type annotations in there, and loose
": _*", when converting it to Java. I'd try to come up with Java's
code, but I have no Java REPL to try it out. :-)

--
Daniel C. Sobral

I travel to the future all the time.

[Joshua Serrin]

I recommend writing a small class in Scala that takes in an Array[T]
where T is your type. Then have do the conversion from scala's Array
to scala's List invoke the Scala API and then return back an Array.
Scala does the conversion for you automatically when dealing with
Arrays to/from Java so i think that's actually the preferred way for
integration... I think. I'm sure there's a book out there that
explains that in depth (http://www.manning.com/suereth/).

That's MODULE$ stuff just seems hairy.

[Shairon Toledo]

I've used to use this way

import java.util.{List, ArrayList}

import scala.collection.JavaConverters._

val jlist = new ArrayList[String]

jlist.add("foo")

jlist.add("bar")

val slist = jlist.asScala.toList

although I don't know if it's the more effective way to do it but it's easier.

--

Shairon Toledo
http://hashcode.me

[Daniel Sobral]

Yeah, but that's in Scala, with implicits. From Java, things are more difficult.

[Daniel Sobral]

The MODULE$ stuff is just the way to use methods from objects. If you
are interacting with Scala from Java, you'd better get used to it.