Converting Map[String, Double] to java.util.Map[String, java.lang.Double]

Question

I thought we can rely on implicit conversion which converts scala.Double to java.lang.Double. So I tried the following:

import scal         


        

Answer 1

The issue here is that scala.Double is a primitive (equivalent to Java double) while java.lang.Double is a class. They are not at all the same thing. The JavaConverters converts between Java Map and Scala Map, not their contents. This works:

import scala.collection.JavaConverters._

object Main {

  def main(args: Array[String]): Unit = {
    val m = Map("10" -> 20.0)
    doSome(mapConv(m))
    doSome2(m.asJava)
  }
  def doSome(m: java.util.Map[java.lang.String, java.lang.Double]) = println(m)
  def doSome2(m: java.util.Map[java.lang.String, Double]) = println(m)

  def mapConv(msd: Map[String, Double]): java.util.Map[java.lang.String, java.lang.Double] = {
    msd.map { case (k, v) => (k -> new java.lang.Double(v)) }.asJava
  }
}