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Object 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]

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
Linear Supertypes
StreamExtensions, AnyRef, Any

Type Members

implicit class AnyArrayHasSeqParStream[A <: AnyRef] extends AnyRef

Definition Classes
StreamExtensions

implicit class ByteArrayHasSeqParStream extends AnyRef

Definition Classes
StreamExtensions

implicit class CharArrayHasSeqParStream extends AnyRef

Definition Classes
StreamExtensions

implicit class DoubleArrayHasSeqParStream extends AnyRef

Definition Classes
StreamExtensions

implicit class DoubleStreamHasToScala extends AnyRef

Definition Classes
StreamExtensions

implicit class FloatArrayHasSeqParStream extends AnyRef

Definition Classes
StreamExtensions

implicit class IntArrayHasSeqParStream extends AnyRef

Definition Classes
StreamExtensions

implicit class IntStreamHasToScala extends AnyRef

Definition Classes
StreamExtensions

implicit class IterableHasSeqStream[A] extends AnyRef

Definition Classes
StreamExtensions

implicit class IterableNonGenericHasParStream[A, C <: IterableOnce[_]] extends AnyRef

Definition Classes
StreamExtensions

implicit class LongArrayHasSeqParStream extends AnyRef

Definition Classes
StreamExtensions

implicit class LongStreamHasToScala extends AnyRef

Definition Classes
StreamExtensions

implicit class MapHasParKeyValueStream[K, V, CC[X, Y] <: MapOps[X, Y, Map, _]] extends AnyRef

Definition Classes
StreamExtensions

implicit class MapHasSeqKeyValueStream[K, V, CC[X, Y] <: MapOps[X, Y, Map, _]] extends AnyRef

Definition Classes
StreamExtensions

implicit class ShortArrayHasSeqParStream extends AnyRef

Definition Classes
StreamExtensions

implicit class StepperHasParStream[A] extends AnyRef

Definition Classes
StreamExtensions

implicit class StepperHasSeqStream[A] extends AnyRef

Definition Classes
StreamExtensions

implicit class StreamHasToScala[A] extends AnyRef

Definition Classes
StreamExtensions

implicit class StringHasSeqParStream extends AnyRef

Definition Classes
StreamExtensions

Value Members

final def !=(arg0: Any): Boolean

Test two objects for inequality.

returns

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

Definition Classes
AnyRef → Any

final def ##(): Int

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

final def ==(arg0: Any): Boolean

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

final def asInstanceOf[T0]: 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.

def clone(): AnyRef

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

final def eq(arg0: AnyRef): Boolean

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

def equals(arg0: AnyRef): Boolean

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

def finalize(): Unit

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

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

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()

def hashCode(): Int

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()

final def isInstanceOf[T0]: Boolean

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

final def ne(arg0: AnyRef): Boolean

Equivalent to !(this eq that).

returns

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

Definition Classes
AnyRef

final def notify(): Unit

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

final def notifyAll(): Unit

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

final def synchronized[T0](arg0: => T0): T0

Definition Classes
AnyRef

def toString(): String

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

final def wait(): Unit

Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException])

final def wait(arg0: Long, arg1: Int): Unit

Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException])

final def wait(arg0: Long): Unit

Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException]) @native()

© 2002-2019 EPFL, with contributions from Lightbend.
Licensed under the Apache License, Version 2.0.
https://www.scala-lang.org/api/2.13.0/scala/jdk/StreamConverters$.html