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Editorial Team
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Asked: 2026-05-31T06:04:36+00:00

I’d like to convert a scala map with a Boolean value to a java

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I’d like to convert a scala map with a Boolean value to a java map with a java.lang.Boolean value (for interoperability).

import scala.collection.JavaConversions._

val a = Map[Int, Boolean]( (1, true), (2, false) )
val b : java.util.Map[Int, java.lang.Boolean] = a

fails with:

error: type mismatch;
found   : scala.collection.immutable.Map[Int,scala.Boolean]
required: java.util.Map[Int,java.lang.Boolean]
val b : java.util.Map[Int, java.lang.Boolean] = a

The JavaConversions implicit conversions work happily with containers parameterized on the same types, but don’t know about the conversion between Boolean & java.lang.Boolean.

Can I use the JavaConversions magic to do this conversion, or is there a concise syntax for doing the conversion without using the implicit conversions in that package?

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1 Answer

  1. Editorial Team

    While JavaConversions will convert the Scala Map to a java.util.Map, and Scala implicitly converts scala.Boolean to java.lang.Boolean, Scala won’t perform two implicit conversions to get the type you want.

    Boolean provides a box method for explicit conversion.

    val b: java.util.Map[Int, java.lang.Boolean] = a.mapValues(Boolean.box)

    If you’re doing this frequently in your code, you can define your own implicit conversion for all Map[T, Boolean].

    import scala.collection.JavaConversions._

implicit def boolMap2Java[T](m: Map[T, Boolean]): 
  java.util.Map[T, java.lang.Boolean] = m.mapValues(Boolean.box)

val b: java.util.Map[Int, java.lang.Boolean] = a
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