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 = 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 |
---|---|
| |
| |
| |
| |
| |
| |
Strings | |
Java streams | |
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
- Alphabetic
- By Inheritance
- StreamConverters
- StreamExtensions
- AnyRef
- Any
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- Public
- Protected
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
This is the documentation for the Scala standard library.
Package structure
The scala package contains core types like
Int
,Float
,Array
orOption
which are accessible in all Scala compilation units without explicit qualification or imports.Notable packages include:
scala.collection
and its sub-packages contain Scala's collections frameworkscala.collection.immutable
- Immutable, sequential data-structures such asVector
,List
,Range
,HashMap
orHashSet
scala.collection.mutable
- Mutable, sequential data-structures such asArrayBuffer
,StringBuilder
,HashMap
orHashSet
scala.collection.concurrent
- Mutable, concurrent data-structures such asTrieMap
scala.concurrent
- Primitives for concurrent programming such asFutures
andPromises
scala.io
- Input and output operationsscala.math
- Basic math functions and additional numeric types likeBigInt
andBigDecimal
scala.sys
- Interaction with other processes and the operating systemscala.util.matching
- Regular expressionsOther packages exist. See the complete list on the right.
Additional parts of the standard library are shipped as separate libraries. These include:
scala.reflect
- Scala's reflection API (scala-reflect.jar)scala.xml
- XML parsing, manipulation, and serialization (scala-xml.jar)scala.collection.parallel
- Parallel collections (scala-parallel-collections.jar)scala.util.parsing
- Parser combinators (scala-parser-combinators.jar)scala.swing
- A convenient wrapper around Java's GUI framework called Swing (scala-swing.jar)Automatic imports
Identifiers in the scala package and the
scala.Predef
object are always in scope by default.Some of these identifiers are type aliases provided as shortcuts to commonly used classes. For example,
List
is an alias forscala.collection.immutable.List
.Other aliases refer to classes provided by the underlying platform. For example, on the JVM,
String
is an alias forjava.lang.String
.