Using scala vararg methods in java

Question

Why do all scala vararg methods, when used from java, seem to accept a Seq of variables, and can't be used as java native vararg methods. Is this a bug?

For instance, Buffer has method def append(elems: A*): Unit. But in java it has another signature: void append(Seq<A>).

score 17 · Answer 1 · answered Oct 31 '12 at 15:02

17

If you control the scala code you can use @varargs to make it generate a java-compatible varags method, e.g. @varargs def append(elems: A*): Unit = {}

answered Oct 31 '12 at 15:02

lmm

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score 8 · Accepted Answer · answered Nov 29 '11 at 15:07

8

It is not a bug. It is a design choice that favors vararg use within Scala over interoperability with Java. For example, it allows you to pass a List into a Scala varargs method without having to convert it to an Array on the way.

If you need to use Scala varargs from Java, you should create some scala Seq instead. You can, for example, write a Java wrapper to get an array automatically created, and then use the genericWrapArray method from the Predef object.

answered Nov 29 '11 at 15:07

Rex Kerr

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For more details, see http://stackoverflow.com/questions/10060377/how-to-use-scala-varargs-from-java-code – Seth Tisue Apr 15 '15 at 16:14

David · Answer 3 · 2011-11-29T11:08:29.457

-6

you can easily cast a Seq in varargs using :_*. For example :

val b = collection.mutable.ListBuffer.empty[Int]
b.append(List(1, 2):_*)

so this avoid code duplication in the collection API.

You can also simply use appendAll :

b.appendAll((List(1, 2))

edited Nov 29 '11 at 11:08

answered Nov 29 '11 at 10:54

David

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Well, yes, I can, but how does that answer my question?)) – F0RR Nov 29 '11 at 11:05
I've just modified my answer. – David Nov 29 '11 at 11:09
The problem is not that Seq can't be casted to varargs in scala. The problem is that I have to create a Seq in Java to use a method with varargs. – F0RR Nov 29 '11 at 11:11
Downvoted as you are still answwering a different question than the one asked. – Dave Griffith Nov 29 '11 at 11:24

Using scala vararg methods in java

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