How to use Scala varargs from Java code

Question

There are plenty of articles on calling Java varargs from Scala code, but the only thing I could find the opposite way round was this question: Using scala vararg methods in

Answer 1

You can use:

scala.collection.Seq$.MODULE$.empty();

from Java code to create an empty sequence. Otherwise, you can use:

new scala.collection.mutable.ArrayBuffer();

to create an empty array buffer into which you can then add elements and use it as an argument to Scala vararg methods.

Otherwise, if you design a Scala library with vararg methods which you want to use from Java code, then use the varargs annotation. It will generate a Java version of the method which takes an array instead of a Seq.

scala> class A {
     |   @annotation.varargs def foo(x: Int*) { println(x) }
     | }
defined class A

scala> println(classOf[A].getMethods.toList)
List(public void $line1.$read$$iw$$iw$A.foo(scala.collection.Seq), public void $line1.$read$$iw$$iw$A.foo(int[]), ...)

Above, reflection shows that there are 2 versions of method foo generated - one that takes a Seq[Int] and another which takes an int[].