This object provides extension methods that convert between Scala and Java collections.

When writing Java code, use the explicit conversion methods defined in javaapi.CollectionConverters instead.

Note: to create Java Streams that operate on Scala collections (sequentially or in parallel), use StreamConverters.

import scala.jdk.CollectionConverters._ val s: java.util.Set[String] = Set("one", "two").asJava

The conversions return adapters for the corresponding API, i.e., the collections are wrapped, not converted. Changes to the original collection are reflected in the view, and vice versa:

scala> import scala.jdk.CollectionConverters._ scala> val s = collection.mutable.Set("one") s: scala.collection.mutable.Set[String] = HashSet(one) scala> val js = s.asJava js: java.util.Set[String] = [one] scala> js.add("two") scala> s res2: scala.collection.mutable.Set[String] = HashSet(two, one)

The following conversions are supported via asScala and asJava:

scala.collection.Iterable <=> java.lang.Iterable scala.collection.Iterator <=> java.util.Iterator scala.collection.mutable.Buffer <=> java.util.List scala.collection.mutable.Set <=> java.util.Set scala.collection.mutable.Map <=> java.util.Map scala.collection.concurrent.Map <=> java.util.concurrent.ConcurrentMap

The following conversions are supported via asScala and through specially-named extension methods to convert to Java collections, as shown:

scala.collection.Iterable <=> java.util.Collection (via asJavaCollection) scala.collection.Iterator <=> java.util.Enumeration (via asJavaEnumeration) scala.collection.mutable.Map <=> java.util.Dictionary (via asJavaDictionary)

In addition, the following one-way conversions are provided via asJava:

scala.collection.Seq => java.util.List scala.collection.mutable.Seq => java.util.List scala.collection.Set => java.util.Set scala.collection.Map => java.util.Map

The following one way conversion is provided via asScala:

java.util.Properties => scala.collection.mutable.Map

In all cases, converting from a source type to a target type and back again will return the original source object. For example:

import scala.jdk.CollectionConverters._ val source = new scala.collection.mutable.ListBuffer[Int] val target: java.util.List[Int] = source.asJava val other: scala.collection.mutable.Buffer[Int] = target.asScala assert(source eq other)
class Object
trait Matchable
class Any

Type members

Inherited classlikes

class ConcurrentMapHasAsJava[K, V](m: Map[K, V])
class MapHasAsJava[K, V](m: Map[K, V])
class MapHasAsScala[K, V](m: Map[K, V])
class MutableMapHasAsJava[K, V](m: Map[K, V])
class SeqHasAsJava[A](s: Seq[A])
class SetHasAsJava[A](s: Set[A])
class SetHasAsScala[A](s: Set[A])