scala: classcast exception: java.util.HashMap cannot be cast to scala.collection.immutable.Map

Question

I have a scala code snippet given below:

// country code to nameToPlaces traversable
val input : Traversable[(Int, java.util.Map[String, java.util.Set[String]])] ... 
val nameToPlacesMap : Map[String, Set[String]] = input.toMap.
            values.
            map (x => x.toSeq).    // throws a class cast exception
            reduce((x,y) => x ++ y).
            groupBy(_._1).
            mapValues(_.map(_._2).
            reduce((x,y)=>x.toSet ++ y.toSet))

nameToPlacesMap is expected to collate all nameToPlaces from all countries. However, while running this code, i am getting a classcastexception

 java.util.HashMap cannot be cast to scala.collection.immutable.Map

I have tried adding asScala but of no use. I am also importing import scala.collection.JavaConverters._ Any help will be appreciated.

NOTE: I don't see this question as a duplicate of a generic classcast exception as noted below: Please revise your judgement.

Your code doesn't compile (too many argument to Traversable). Please edit your post and correct it. Also, it would be useful to know where you put `.asScala`. — The Archetypal Paul, Oct 04 '15 at 07:33
Try looking at [this](http://stackoverflow.com/questions/3127238/convert-java-util-mapstring-object-to-scala-collection-immutable-mapstring) — Avihoo Mamka, Oct 04 '15 at 07:34
Is there a special reason why you are mixing Java and Scala collections? If your program is only Scala, then don't use Java collections. — Jesper, Oct 04 '15 at 07:45
Could you try `input.flatMap(_._2.asScala).groupBy(_._1).mapValues(_.map(_._2.toSet).reduce(_ ++ _))` ? You need to import both `JavaConversions._` and `JavaConverters._` for that. — Kolmar, Oct 04 '15 at 11:23

Sascha Kolberg · Answer 1 · 2015-10-05T07:27:07.740

0

You have several java collections in your outer map, you have to make sure to convert them all. As far as I can see, the following should work for you:

import java.util

import scala.collection.JavaConverters._
import scala.collection.mutable

val input : Traversable[(Int, java.util.Map[String, java.util.Set[String]])] =
  Seq((1, new util.HashMap[String, java.util.Set[String]]()))

val nameToPlacesMap : Map[String, mutable.Set[String]] = input.toMap.mapValues(
  // convert inner Map
  _.asScala.mapValues(
    // convert java.util.Set
    mutable.Set.empty ++ _.asScala)
  ).values.
            map (x => x.toSeq).    // hopefully not anymore :: throws a class cast exception
            reduce((x,y) => x ++ y).
  groupBy(_._1).
  mapValues(_.map(_._2).
    reduce((x,y)=> x ++ y))

edited Oct 05 '15 at 07:27

answered Oct 04 '15 at 07:32

Sascha Kolberg

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Hi Sasche, i get the compiling error: value asScala is not a member of Traversable – Amm Sokun Oct 04 '15 at 10:13
I was not so sure about the outermost traversable, just try to leave out the first 'asScala' – Sascha Kolberg Oct 04 '15 at 12:10
@AmmSokun I edited my answer, to treat the outer most `Traversable` as scala collection – Sascha Kolberg Oct 04 '15 at 17:21
it still doesn't compile, after removing the outmost asScala, next one gives the error and fails to compile – Amm Sokun Oct 05 '15 at 05:55
@AmmSokun I missed some confusion about mutable and immutable `Set` as well as import of required converters. I edited my answer to a version, that at least on my machine, compiles. – Sascha Kolberg Oct 05 '15 at 07:26

scala: classcast exception: java.util.HashMap cannot be cast to scala.collection.immutable.Map

1 Answers1