Convert java.util.Set to scala.collection.Set

Question

How can I convert a java.util.Set[String] to a scala.collection.Set with a generic type in Scala 2.8.1?

import scala.collection.JavaConversions._

var in : java.util.Set[String] = new java.util.HashSet[String]()

in.add("Oscar")
in.add("Hugo")

val out : scala.collection.immutable.Set[String] = Set(in.toArray : _*)

And this is the error message

<console>:9: error: type mismatch;  
found   : Array[java.lang.Object]
required: Array[_ <: String]   
val out : scala.collection.immutable.Set[String] = Set(javaset.toArray : _*)

What am I doing wrong?

score 25 · Answer 1 · edited May 27 '11 at 06:22

25

Use JavaConverters instead

import scala.collection.JavaConverters._

val out = in.asScala

out: scala.collection.mutable.Set[String] = Set(Hugo, Oscar)

edited May 27 '11 at 06:22

missingfaktor

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answered May 26 '11 at 19:34

oluies

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Oddly, but this import statement fails: import scala.collection.JavaConverters._ I use Scala version 2.8.1 – Twistleton May 26 '11 at 19:44
JavaConverters is avaliable Since 2.8.1 – oluies May 26 '11 at 19:48
this gives scala.collection.mutable.Set and I need scala.collection.immutable.Set – khush Jul 18 '22 at 09:34

score 16 · Accepted Answer · edited May 23 '17 at 12:25

16

toArray() called on a java Set will return an array of Object. Since you already imported JavaConversions, asScalaSet will implicitly convert your Java set to a mutable Scala set or use toSet to convert it to an immutable set.

See also Convert Scala Set into Java (java.util.Set)

edited May 23 '17 at 12:25

Community

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answered May 26 '11 at 19:35

Mark Jayxcela

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I read them, but the function asSet doesn't work. With toSet is works fine. Thank you very much. – Twistleton May 26 '11 at 19:40
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FYI JavaConversions is deprecated as of Scala 2.12.0. Use JavaConverters. – lznt Dec 05 '18 at 19:39

Convert java.util.Set to scala.collection.Set

2 Answers2