How to pass Scala Seq to a Java varargs

Question

I have an existing Java method like this:

public static MyJavaClass javaFunc(String name, long... values) {
    ...
}

and I need to call it from Scala with this:

val idList: Seq[Long] = Seq(1L, 2L, 3L)

MyJavaClass.javaFunc("hello", idList)

but it ends up invoking the toString method on the idList parameter. I've tried the following to no avail:

MyJavaClass.javaFunc("hello", idList:_*)

which causes compile error:

no `: _*' annotation allowed here (such annotations are only allowed in arguments to *-parameters)

How can I pass the argument?

This sounds more like a compiler error, that confuses me a bit. Does this class have other constructors? — drexin, Jun 14 '13 at 19:38
Can't reproduce it either. BTW which Scala version are you using? — Beryllium, Jun 14 '13 at 19:39
There are lots of them that look the same but slightly different. This is actually an ElasticSearch class: FilterBuilders.TermsFilterBuilder — OutNSpace, Jun 14 '13 at 19:40
Using Scala 2.10 - you are right - it is a compile error. But still, how do I call it? — OutNSpace, Jun 14 '13 at 19:41
Just to be sure, there is TermFilterBuilder, which takes only a single long and TermsFilterBuilder, which takes the varargs. Did you check for a typo? — drexin, Jun 14 '13 at 19:49
In case anyone is wondering what `:_*` is: http://stackoverflow.com/a/6051356/194894 — Flow, Mar 24 '16 at 13:56

chuchulo · Answer 1 · 2020-06-20T14:47:31.263

3

// java class
public class MyJavaClass {
    public static void javaFunc(String name, long ...values) {
        for (long i: values)
            System.out.print(i + " ");
        System.out.println();
    }
}

//scala class
object Y {
  def main(args: Array[String]): Unit = {
    val idList: Seq[Long] = Seq(1L, 2L, 3L)
    MyJavaClass.javaFunc("hello", idList: _*)
  }
}

it is working like this for me

edited Jun 20 '20 at 14:47

answered Jun 20 '20 at 14:38

chuchulo

61
6

score 0 · Answer 2 · answered Jun 03 '20 at 07:53

I can't reproduce this on Scala 2.10.4 and Java 8 but it seems like a bug.

You can avoid the : _* by adding these Java methods:

public static MyJavaClass javaFuncConverter(String name, long[] values) {
     return javaFunc(name, values);
}

public static MyJavaClass javaFuncConverter(String name, long value) {
     return javaFunc(name, value);
}

In your Scala code you call it like this:

val idList: Seq[Long] = Seq(1L, 2L, 3L)

MyJavaClass.javaFuncConverter("hello", idList.toArray)
MyJavaClass.javaFuncConverter("hello", idList.head)

score -1 · Answer 3 · answered Jun 14 '13 at 20:15

-1

This did the trick:

import scala.collection.JavaConverters._
val javaList = idList.asJava

answered Jun 14 '13 at 20:15

OutNSpace

373
2
8

8

You've got a java List now. So, how you going to pass it into parameter as java's varargs? – Dmitry Bespalov Aug 06 '15 at 10:29

How to pass Scala Seq to a Java varargs

3 Answers3