CODEWITHSUNDEEP
scalatype-conversionscala-collectionsscala-2.8scala-java-interop
or9ob
or9ob

Reputation: 2392

Convert Scala Set into Java (java.util.Set)?

I have a Set in Scala (I can choose any implementation as I am creating the Set. The Java library I am using is expecting a java.util.Set[String].

Is the following the correct way to do this in Scala (using scala.collection.jcl.HashSet#underlying):

import com.javalibrary.Animals

var classes = new scala.collection.jcl.HashSet[String]
classes += "Amphibian"
classes += "Reptile"
Animals.find(classes.underlying)

It seems to be working, but since I am very new to Scala I want to know if this is the preferred way (any other way I try I am getting a type-mismatch error):

error: type mismatch;
 found   : scala.collection.jcl.HashSet[String]
 required: java.util.Set[_]

Upvotes: 28

Views: 17533

Answers (5)

Xavier Guihot
Xavier Guihot

Reputation: 61666

Note that starting Scala 2.13, package scala.jdk.CollectionConverters replaces deprecated packages scala.collection.JavaConverters/JavaConversions._:

import scala.jdk.CollectionConverters._

// val scalaSet: Set[String] = Set("a", "b")
val javaSet = scalaSet.asJava
// javaSet: java.util.Set[String] = [a, b]
javaSet.asScala
// scala.collection.mutable.Set[String] = Set(a, b)

Upvotes: 8

Nik Kashi
Nik Kashi

Reputation: 4596

In Scala 2.12 it is possible to use : scala.collection.JavaConverters.setAsJavaSet(scalaSetInstance)

Upvotes: 4

mixel
mixel

Reputation: 25846

Since Scala 2.12.0 scala.collection.JavaConversions is deprecated:

Therefore, this API has been deprecated and JavaConverters should be used instead. JavaConverters provides the same conversions, but through extension methods.

And since Scala 2.8.1 you can use scala.collection.JavaConverters for this purpose:

import scala.collection.JavaConverters._
val javaSet = new java.util.HashSet[String]()
val scalaSet = javaSet.asScala
val javaSetAgain = scalaSet.asJava

Upvotes: 11

Viktor Klang
Viktor Klang

Reputation: 26579

For 2.7.x I highly recommend using: http://github.com/jorgeortiz85/scala-javautils

Upvotes: 5

Randall Schulz
Randall Schulz

Reputation: 26486

If you were asking about Scala 2.8, Java collections interoperability is supplied by scala.collection.JavaConversions. In this case, you want JavaConversions.asSet(...) (there's one for each direction, Java -> Scala and Scala -> Java).

For Scala 2.7, each scala.collection.jcl class that wraps a Java collection has an underlying property which provides the wrapped Java collection instance.

Upvotes: 24

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