Scala convert List[Int] to a java.util.List[java.lang.Integer]

Question

Is there a way in Scala to convert a List[Int] to java.util.List[java.lang.Integer]?

I\'m interfacing with Java (Thrift).

Answer 1

This doesn't have an implicit at the outmost layer, but I like this generic approach and have implemented it for a couple of types of collections (List, Map).

import java.util.{List => JList}
import scala.collection.JavaConverters._

  def scalaList2JavaList[A, B](scalaList: List[A])
                              (implicit a2bConversion: A => B): JList[B] =
    (scalaList map a2bConversion).asJava

Since an implicit conversion from Int to Integer is part of standard lib, usage in this case would just look like this:

  scalaList2JavaList[Int, Integer](someScalaList)

In the other direction!

(since I have these available anyway as they were my original implementations...)

import java.util.{List => JList}
import scala.collection.JavaConversions._

  def javaList2ScalaList[A, B](javaList: JList[A])
                              (implicit a2bConversion: A => B): List[B] =
    javaList.toList map a2bConversion

Usage:

  javaList2ScalaList[Integer, Int](someJavaList)

This can then be re-used for all lists so long as an implicit conversion of the contained type is in scope.

(And in case you're curious, here is my implementation for map...)

  def javaMap2ScalaMap[A, B, C, D](javaMap: util.Map[A, B])(implicit a2cConversion: A => C, b2dConversion: B => D): Map[C, D] =
    javaMap.toMap map { case (a, b) => (a2cConversion(a), b2dConversion(b)) }