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A library for converting between Java and Scala collections.


Turn any Scala collection into the corresponding Java collection:

import scalaj.collection.Imports._

List(1, 2, 3).asJava
// returns java.util.List[java.lang.Integer]

Map(1 -> "a", 2 -> "b", 3 -> "c").asJava
// returns java.util.Map[java.lang.Integer, java.lang.String]

Set(1, 2, 3).asJava
// returns java.util.Set[java.lang.Integer]

Turn any Java collection into the corresponding Scala collection:

val list = new java.util.ArrayList[java.lang.Integer]
// returns scala.Seq[Int]

As shown in the above examples, the library also converts between the boxed types of Scala and Java primitives.

You can also use foreach on any Java collection:

// prints "123"

The map, filter, and flatMap methods are still pending.


scalaj-collection requires Scala 2.9.x, 2.10.x or 2.11.x



If you're using sbt, simply add the following line to your project file:

libraryDependencies += "org.scalaj" %% "scalaj-collection" % "1.6"


If you're using Maven, add the following to your pom.xml:



Download the jars from

From source

Clone the repository from Github:

git clone git://

Build the project and create the JAR (requires sbt version 0.12.4 or greater):

cd scalaj-collection
sbt package


The following methods are added via the Swag My Library pattern:

// Java to Scala
java.lang.Comparable[A]   #asScala: scala.math.Ordered[A]
java.util.Comparator[A]   #asScala: scala.math.Ordering[A]
java.util.Enumeration[A]  #asScala: scala.collection.Iterator[A]
                          #foreach(A => Unit): Unit
java.util.Iterator[A]     #asScala: scala.collection.Iterator[A]
                          #foreach(A => Unit): Unit
java.lang.Iterable[A]     #asScala: scala.collection.Iterable[A]
                          #foreach(A => Unit): Unit
java.util.List[A]         #asScala: scala.collection.Seq[A]
                          #asScalaMutable: scala.collection.mutable.Seq[A]
java.util.Set[A]          #asScala: scala.collection.Set[A]
                          #asScalaMutable: scala.collection.mutable.Set[A]
java.util.Map[A, B]       #asScala: scala.collection.Map[A, B]
                          #asScalaMutable: scala.collection.mutable.Map[A, B]
                          #foreach(((A, B)) => Unit): Unit
java.util.Dictionary[A, B]#asScala: scala.collection.mutable.Map[A, B]
                          #foreach(((A, B)) => Unit): Unit

// Scala to Java
scala.math.Ordered[A]             #asJava: java.util.Comparable[A]
scala.math.Ordering[A]            #asJava: java.util.Comparator[A]
scala.collection.Iterator[A]      #asJava: java.util.Iterator[A]
                                  #asJavaEnumeration: java.util.Enumeration[A]
scala.collection.Iterable[A]      #asJava: java.lang.Iterable[A]
scala.collection.Seq[A]           #asJava: java.util.List[A]
scala.collection.mutable.Seq[A]   #asJava: java.util.List[A]
scala.collection.mutable.Buffer[A]#asJava: java.util.List[A]
scala.collection.Set[A]           #asJava: java.util.Set[A]
scala.collection.mutable.Set[A]   #asJava: java.util.Set[A]
scala.collection.Map[A, B]        #asJava: java.util.Map[A, B]
scala.collection.mutable.Map[A, B]#asJava: java.util.Map[A, B]
                                  #asJavaDictionary: java.util.Dictionary[A, B]
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