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

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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[_]
scala-2.8 scala-collections scala-java-interop type-conversion scala
5 Answers

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.

user_2001660
user_2278030

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)
user_92971440
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