How to convert Scala collection Seq[(Int, Seq[String])] to Java collection List[(int, List[String])]?

Question

I know that there are two extremely useful objects in scala.collection package, which will help us to achieve this goal:

JavaConverters (If I want to be explicit and tell exactly what I want to convert)
JavaConversions (If I don’t want co control conversions and let compiler make implicit work for me)

but I have some troubles to apply them in my case because my data structure is a little bit more complex than the other ones that I saw in many examples.

I'm in scala code and I want that my scala function return a Java collection. So I wanto to convert Scala Seq[(Int, Seq[String])] to Java collection List[(int, List[String])].

How can I do this?

T. Gawęda · Accepted Answer · 2018-01-19 18:13:41Z

7

Use map to at first map Seq[(Int, Seq[String])] to Seq[(Int, List[String])] and then use again the same function to main collection

import scala.collection.JavaConversions
val seq : Seq[(Int, Seq[String])] = some code
val seqOfLists = seq.map(s => (s._1, JavaConversions.seqAsJavaList(s._2)))
val listOfLists = JavaConversions.seqAsJavaList(seqOfLists)

Or newer API:

import scala.collection.JavaConverters._
val seq : Seq[(Int, Seq[String])] = some code
val seqOfLists = seq.map(s => (s._1, s._2.asJava))
val listOfLists = seqOfLists.asJava

edited Jan 19, 2018 at 18:13

answered Jan 19, 2018 at 17:46

T. Gawęda

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12 Comments

T. Gawęda Over a year ago

@AlexSavitsky Ok I added newer API. I didn't notice deprecation, nice catch

T. Gawęda Over a year ago

@AlexSavitsky BTW, Thanks for information why you downvoted - that caused that I had possibility to change the question and also learn something. That is very community-friendly way of improvements in answers ;)

Alex Savitsky Over a year ago

Upvoted it back. This is a great example of positive collaboration.

T. Gawęda Over a year ago

@Fobi note () - it's a normal Java function

T. Gawęda Over a year ago

@Fobi Full signature is List<Tuple2<Int, List<String>>>

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Jeffrey Chung · Accepted Answer · 2018-01-19 18:03:46Z

3

JavaConversions is deprecated since Scala 2.12.0. Use JavaConverters instead:

import scala.collection.JavaConverters._

val seq: Seq[(Int, Seq[String])] = ???
val javaList = seq.map(x => (x._1, x._2.asJava)).asJava
// java.util.List[(Int, java.util.List[String])]

answered Jan 19, 2018 at 18:03

Jeffrey Chung

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