Packages

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scala.jdk

StreamConverters

object StreamConverters extends StreamExtensions

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 = [email protected]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.

Source
StreamConverters.scala
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Type Members

  1. implicit class AnyArrayHasSeqParStream[A <: AnyRef] extends AnyRef
    Definition Classes
    StreamExtensions
  2. implicit class ByteArrayHasSeqParStream extends AnyRef
    Definition Classes
    StreamExtensions
  3. implicit class CharArrayHasSeqParStream extends AnyRef
    Definition Classes
    StreamExtensions
  4. implicit class DoubleArrayHasSeqParStream extends AnyRef
    Definition Classes
    StreamExtensions
  5. implicit class DoubleStreamHasToScala extends AnyRef
    Definition Classes
    StreamExtensions
  6. implicit class FloatArrayHasSeqParStream extends AnyRef
    Definition Classes
    StreamExtensions
  7. implicit class IntArrayHasSeqParStream extends AnyRef
    Definition Classes
    StreamExtensions
  8. implicit class IntStreamHasToScala extends AnyRef
    Definition Classes
    StreamExtensions
  9. implicit class IterableHasSeqStream[A] extends AnyRef
    Definition Classes
    StreamExtensions
  10. implicit class IterableNonGenericHasParStream[A, C <: IterableOnce[_]] extends AnyRef
    Definition Classes
    StreamExtensions
  11. implicit class LongArrayHasSeqParStream extends AnyRef
    Definition Classes
    StreamExtensions
  12. implicit class LongStreamHasToScala extends AnyRef
    Definition Classes
    StreamExtensions
  13. implicit class MapHasParKeyValueStream[K, V, CC[X, Y] <: MapOps[X, Y, CC, _]] extends AnyRef
    Definition Classes
    StreamExtensions
  14. implicit class MapHasSeqKeyValueStream[K, V, CC[X, Y] <: MapOps[X, Y, CC, _]] extends AnyRef
    Definition Classes
    StreamExtensions
  15. implicit class ShortArrayHasSeqParStream extends AnyRef
    Definition Classes
    StreamExtensions
  16. implicit class StepperHasParStream[A] extends AnyRef
    Definition Classes
    StreamExtensions
  17. implicit class StepperHasSeqStream[A] extends AnyRef
    Definition Classes
    StreamExtensions
  18. implicit class StreamHasToScala[A] extends AnyRef
    Definition Classes
    StreamExtensions
  19. implicit class StringHasSeqParStream extends AnyRef
    Definition Classes
    StreamExtensions
  20. type IterableOnceWithEfficientStepper[A] = collection.IterableOnce[A] { def stepper[B >: A, S <: scala.collection.Stepper[_]](implicit shape: scala.collection.StepperShape[B,S]): S with collection.Stepper.EfficientSplit }
    Attributes
    protected
    Definition Classes
    StreamExtensions

Value Members

  1. final def !=(arg0: Any): Boolean

    Test two objects for inequality.

    Test two objects for inequality.

    returns

    true if !(this == that), false otherwise.

    Definition Classes
    AnyRef → Any
  2. final def ##(): Int

    Equivalent to x.hashCode except for boxed numeric types and null.

    Equivalent to x.hashCode except for boxed numeric types and null. For numerics, it returns a hash value which is consistent with value equality: if two value type instances compare as true, then ## will produce the same hash value for each of them. For null returns a hashcode where null.hashCode throws a NullPointerException.

    returns

    a hash value consistent with ==

    Definition Classes
    AnyRef → Any
  3. final def ==(arg0: Any): Boolean

    The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).

    The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).

    returns

    true if the receiver object is equivalent to the argument; false otherwise.

    Definition Classes
    AnyRef → Any
  4. final def asInstanceOf[T0]: T0

    Cast the receiver object to be of type T0.

    Cast the receiver object to be of type T0.

    Note that the success of a cast at runtime is modulo Scala's erasure semantics. Therefore the expression 1.asInstanceOf[String] will throw a ClassCastException at runtime, while the expression List(1).asInstanceOf[List[String]] will not. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the requested type.

    returns

    the receiver object.

    Definition Classes
    Any
    Exceptions thrown

    ClassCastException if the receiver object is not an instance of the erasure of type T0.

  5. def clone(): AnyRef

    Create a copy of the receiver object.

    Create a copy of the receiver object.

    The default implementation of the clone method is platform dependent.

    returns

    a copy of the receiver object.

    Attributes
    protected[java.lang]
    Definition Classes
    AnyRef
    Annotations
    @throws(classOf[java.lang.CloneNotSupportedException]) @native()
    Note

    not specified by SLS as a member of AnyRef

  6. final def eq(arg0: AnyRef): Boolean

    Tests whether the argument (that) is a reference to the receiver object (this).

    Tests whether the argument (that) is a reference to the receiver object (this).

    The eq method implements an equivalence relation on non-null instances of AnyRef, and has three additional properties:

    • It is consistent: for any non-null instances x and y of type AnyRef, multiple invocations of x.eq(y) consistently returns true or consistently returns false.
    • For any non-null instance x of type AnyRef, x.eq(null) and null.eq(x) returns false.
    • null.eq(null) returns true.

    When overriding the equals or hashCode methods, it is important to ensure that their behavior is consistent with reference equality. Therefore, if two objects are references to each other (o1 eq o2), they should be equal to each other (o1 == o2) and they should hash to the same value (o1.hashCode == o2.hashCode).

    returns

    true if the argument is a reference to the receiver object; false otherwise.

    Definition Classes
    AnyRef
  7. def equals(arg0: AnyRef): Boolean

    The equality method for reference types.

    The equality method for reference types. Default implementation delegates to eq.

    See also equals in scala.Any.

    returns

    true if the receiver object is equivalent to the argument; false otherwise.

    Definition Classes
    AnyRef → Any
  8. def finalize(): Unit

    Called by the garbage collector on the receiver object when there are no more references to the object.

    Called by the garbage collector on the receiver object when there are no more references to the object.

    The details of when and if the finalize method is invoked, as well as the interaction between finalize and non-local returns and exceptions, are all platform dependent.

    Attributes
    protected[java.lang]
    Definition Classes
    AnyRef
    Annotations
    @throws(classOf[java.lang.Throwable])
    Note

    not specified by SLS as a member of AnyRef

  9. final def getClass(): Class[_ <: AnyRef]

    Returns the runtime class representation of the object.

    Returns the runtime class representation of the object.

    returns

    a class object corresponding to the runtime type of the receiver.

    Definition Classes
    AnyRef → Any
    Annotations
    @native()
  10. def hashCode(): Int

    The hashCode method for reference types.

    The hashCode method for reference types. See hashCode in scala.Any.

    returns

    the hash code value for this object.

    Definition Classes
    AnyRef → Any
    Annotations
    @native()
  11. final def isInstanceOf[T0]: Boolean

    Test whether the dynamic type of the receiver object is T0.

    Test whether the dynamic type of the receiver object is T0.

    Note that the result of the test is modulo Scala's erasure semantics. Therefore the expression 1.isInstanceOf[String] will return false, while the expression List(1).isInstanceOf[List[String]] will return true. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the specified type.

    returns

    true if the receiver object is an instance of erasure of type T0; false otherwise.

    Definition Classes
    Any
  12. final def ne(arg0: AnyRef): Boolean

    Equivalent to !(this eq that).

    Equivalent to !(this eq that).

    returns

    true if the argument is not a reference to the receiver object; false otherwise.

    Definition Classes
    AnyRef
  13. final def notify(): Unit

    Wakes up a single thread that is waiting on the receiver object's monitor.

    Wakes up a single thread that is waiting on the receiver object's monitor.

    Definition Classes
    AnyRef
    Annotations
    @native()
    Note

    not specified by SLS as a member of AnyRef

  14. final def notifyAll(): Unit

    Wakes up all threads that are waiting on the receiver object's monitor.

    Wakes up all threads that are waiting on the receiver object's monitor.

    Definition Classes
    AnyRef
    Annotations
    @native()
    Note

    not specified by SLS as a member of AnyRef

  15. final def synchronized[T0](arg0: => T0): T0
    Definition Classes
    AnyRef
  16. def toString(): String

    Creates a String representation of this object.

    Creates a String representation of this object. The default representation is platform dependent. On the java platform it is the concatenation of the class name, "@", and the object's hashcode in hexadecimal.

    returns

    a String representation of the object.

    Definition Classes
    AnyRef → Any
  17. final def wait(): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws(classOf[java.lang.InterruptedException])
  18. final def wait(arg0: Long, arg1: Int): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws(classOf[java.lang.InterruptedException])
  19. final def wait(arg0: Long): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws(classOf[java.lang.InterruptedException]) @native()

Inherited from StreamExtensions

Inherited from AnyRef

Inherited from Any

Ungrouped