Value Members

1.  object Accumulator

   Contains factory methods to build Accumulators.

   Contains factory methods to build Accumulators.

   Note that the Accumulator object itself is not a factory, but it is implicitly convert to a factory according to the element type, see Accumulator.toFactory.

   This allows passing the Accumulator object as argument when a collection.Factory, and the implicit Accumulator.AccumulatorFactoryShape instance is used to build a specialized Accumulator according to the element type:

   scala> val intAcc = Accumulator(1,2,3)
   intAcc: scala.collection.convert.IntAccumulator = IntAccumulator(1, 2, 3)
   
   scala> val anyAccc = Accumulator("K")
   anyAccc: scala.collection.convert.AnyAccumulator[String] = AnyAccumulator(K)
   
   scala> val intAcc2 = List(1,2,3).to(Accumulator)
   intAcc2: scala.jdk.IntAccumulator = IntAccumulator(1, 2, 3)
   
   scala> val anyAcc2 = List("K").to(Accumulator)
   anyAcc2: scala.jdk.AnyAccumulator[String] = AnyAccumulator(K)

2.  object AnyAccumulator extends SeqFactory[AnyAccumulator]
3.  object CollectionConverters extends AsJavaExtensions with AsScalaExtensions

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

   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)

4.  object DoubleAccumulator extends SpecificIterableFactory[Double, DoubleAccumulator] with java.io.Serializable
5.  object DurationConverters

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

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

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

6.  object FunctionConverters extends Priority0FunctionExtensions

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

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

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

   Using the .asJava extension method on a Scala function produces the most specific possible Java function type:

   scala> import scala.jdk.FunctionConverters._
   scala> val f = (x: Int) => x + 1
   
   scala> val jf1 = f.asJava
   jf1: java.util.function.IntUnaryOperator = ...

   More generic Java function types can be created using the corresponding asJavaXYZ extension method:

   scala> val jf2 = f.asJavaFunction
   jf2: java.util.function.Function[Int,Int] = ...
   
   scala> val jf3 = f.asJavaUnaryOperator
   jf3: java.util.function.UnaryOperator[Int] = ...

   Converting a Java function to Scala is done using the asScala extension method:

   scala> List(1,2,3).map(jf2.asScala)
   res1: List[Int] = List(2, 3, 4)

7.  object FunctionWrappers
8.  object FutureConverters

   This object provides extension methods that convert between Scala scala.concurrent.Future and Java java.util.concurrent.CompletionStage

   This object provides extension methods that convert between Scala scala.concurrent.Future and Java java.util.concurrent.CompletionStage

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

   Note that the bridge is implemented at the read-only side of asynchronous handles, namely scala.concurrent.Future (instead of scala.concurrent.Promise) and java.util.concurrent.CompletionStage (instead of java.util.concurrent.CompletableFuture). This is intentional, as the semantics of bridging the write-handles would be prone to race conditions; if both ends (CompletableFuture and Promise) are completed independently at the same time, they may contain different values afterwards. For this reason, toCompletableFuture is not supported on the created CompletionStages.

9.  object IntAccumulator extends SpecificIterableFactory[Int, IntAccumulator] with java.io.Serializable
10.  object LongAccumulator extends SpecificIterableFactory[Long, LongAccumulator] with java.io.Serializable
11.  object OptionConverters

    This object provides extension methods that convert between Scala Option and Java Optional types.

    This object provides extension methods that convert between Scala Option and Java Optional types.

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

    Scala Option is extended with a toJava method that creates a corresponding Optional, and a toJavaPrimitive method that creates a specialized variant (e.g., OptionalInt) if applicable.

    Java Optional is extended with a toScala method and a toJavaPrimitive method.

    Finally, specialized Optional types are extended with toScala and toJavaGeneric methods.

    Example usage:

    import scala.jdk.OptionConverters._
    val a = Option("example").toJava      // Creates java.util.Optional[String] containing "example"
    val b = (None: Option[String]).toJava // Creates an empty java.util.Optional[String]
    val c = a.toScala                     // Back to Option("example")
    val d = b.toScala                     // Back to None typed as Option[String]
    val e = Option(2.7).toJava            // java.util.Optional[Double] containing boxed 2.7
    val f = Option(2.7).toJavaPrimitive   // java.util.OptionalDouble containing 2.7 (not boxed)
    val g = f.toScala                     // Back to Option(2.7)
    val h = f.toJavaGeneric               // Same as e
    val i = e.toJavaPrimitive             // Same as f

12.  object OptionShape
13.  object StreamConverters extends StreamExtensions

    This object provides extension methods to create Java Streams that operate on Scala collections (sequentially or in parallel).

    This object provides extension methods to create Java Streams that operate on Scala collections (sequentially or in parallel). For more information on Java streams, consult the documentation (https://docs.oracle.com/javase/8/docs/api/java/util/stream/package-summary.html).

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

    The methods asJavaSeqStream and asJavaParStream convert a collection to a Java Stream:

    scala> import scala.jdk.StreamConverters._
    
    scala> val s = (1 to 10).toList.asJavaSeqStream
    s: java.util.stream.IntStream = java.util.stream.IntPipeline$Head@7b1e5e55
    
    scala> s.map(_ * 2).filter(_ > 5).toScala(List)
    res1: List[Int] = List(6, 8, 10, 12, 14, 16, 18, 20)

    Note: using parallel streams in the Scala REPL causes deadlocks, see https://github.com/scala/bug/issues/9076. As a workaround, use scala -Yrepl-class-based.

    scala> def isPrime(n: Int): Boolean = !(2 +: (3 to Math.sqrt(n).toInt by 2) exists (n % _ == 0))
    isPrime: (n: Int)Boolean
    
    scala> (10000 to 1000000).asJavaParStream.filter(isPrime).toScala(Vector)
    res6: scala.collection.immutable.Vector[Int] = Vector(10007, 10009, 10037, 10039, ...

    A Java Stream provides operations on a sequence of elements. Streams are created from Spliterators, which are similar to Iterators with the additional capability to partition off some of their elements. This partitioning, if supported by the Spliterator, is used for parallelizing Stream operations.

    Scala collections have a method stepper that returns a scala.collection.Stepper for the collection, which in turn can be converted to a Spliterator for creating a Java Stream.

    The asJavaSeqStream extension method is available on any Scala collection. The asJavaParStream extension method can only be invoked on collections where the return type of the stepper method is marked with the scala.collection.Stepper.EfficientSplit marker trait. This trait is added to steppers that support partitioning, and therefore efficient parallel processing.

    The following extension methods are available:

    Collection Type	Extension Methods
    IterableOnce	asJavaSeqStream
    IndexedSeq, Arrays, BitSet, Accumulator, HashMap, HashSet, Range, TreeMap, TreeSet, Vector, Strings	asJavaParStream
    Map	asJavaSeqKeyStream, asJavaSeqValueStream
    HashMap, TreeMap	asJavaParKeyStream, asJavaParValueStream
    Stepper	asJavaSeqStream
    Stepper with EfficientSplit	asJavaParStream
    Strings	asJavaSeqStream, asJavaParStream, asJavaSeqCharStream, asJavaParCharStream, asJavaSeqCodePointStream, asJavaParCodePointStream
    Java streams	toScala, asJavaPrimitiveStream

    The asJavaPrimitiveStream method converts a Stream[Int] to an IntStream. It is the dual of the boxed method defined on primitive streams (e.g., IntStream.boxed is a Stream[Integer]).

    The toScala extension methods on Java streams collects the result of a stream pipeline into a Scala collection, for example stream.toScala(List), stream.toScala(Vector). Note that transformation operations on streams are lazy (also called "intermediate"), terminal operations such as forEach, count or toScala trigger the evaluation.

    Collecting a parallel stream to a collection can be performed in parallel. This is beneficial if the target collection supports efficient merging of the segments that are built in parallel. To support this use case, the Scala standard library provides the Accumulator collection. This collection supports efficient parallel construction, and it has specialized subtypes for Int, Long and Double so that primitive Java streams can be collected to a Scala collection without boxing the elements.