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
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- StreamConverters
- StreamExtensions
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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.
Test two objects for inequality.
- returns
trueif !(this == that), false otherwise.
- Definition Classes
- AnyRef → Any
- final def ##(): Int
Equivalent to
x.hashCodeexcept for boxed numeric types andnull.Equivalent to
x.hashCodeexcept for boxed numeric types andnull. 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. Fornullreturns a hashcode wherenull.hashCodethrows aNullPointerException.- returns
a hash value consistent with ==
- Definition Classes
- AnyRef → Any
- final def ==(arg0: Any): Boolean
The expression
x == thatis equivalent toif (x eq null) that eq null else x.equals(that).The expression
x == thatis equivalent toif (x eq null) that eq null else x.equals(that).- returns
trueif the receiver object is equivalent to the argument;falseotherwise.
- Definition Classes
- AnyRef → Any
- 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 aClassCastExceptionat runtime, while the expressionList(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
ClassCastExceptionif the receiver object is not an instance of the erasure of typeT0.
- def clone(): AnyRef
Create a copy of the receiver object.
Create a copy of the receiver object.
The default implementation of the
clonemethod is platform dependent.- returns
a copy of the receiver object.
- 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
eqmethod implements an equivalence relation on non-null instances ofAnyRef, and has three additional properties:- It is consistent: for any non-null instances
xandyof typeAnyRef, multiple invocations ofx.eq(y)consistently returnstrueor consistently returnsfalse. - For any non-null instance
xof typeAnyRef,x.eq(null)andnull.eq(x)returnsfalse. null.eq(null)returnstrue.
When overriding the
equalsorhashCodemethods, 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
trueif the argument is a reference to the receiver object;falseotherwise.
- Definition Classes
- AnyRef
- It is consistent: for any non-null instances
- def equals(arg0: AnyRef): Boolean
The equality method for reference types.
- 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
finalizemethod is invoked, as well as the interaction betweenfinalizeand non-local returns and exceptions, are all platform dependent.- Attributes
- protected[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.
- def hashCode(): Int
The hashCode method for reference types.
- 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 returnfalse, while the expressionList(1).isInstanceOf[List[String]]will returntrue. 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
trueif the receiver object is an instance of erasure of typeT0;falseotherwise.
- Definition Classes
- Any
- final def ne(arg0: AnyRef): Boolean
Equivalent to
!(this eq that).Equivalent to
!(this eq that).- returns
trueif the argument is not a reference to the receiver object;falseotherwise.
- Definition Classes
- AnyRef
- 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
- 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
- final def synchronized[T0](arg0: => T0): T0
- Definition Classes
- AnyRef
- 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
- 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
This is the documentation for the Scala standard library.
Package structure
The scala package contains core types like
Int,Float,ArrayorOptionwhich are accessible in all Scala compilation units without explicit qualification or imports.Notable packages include:
scala.collectionand its sub-packages contain Scala's collections frameworkscala.collection.immutable- Immutable, sequential data-structures such asVector,List,Range,HashMaporHashSetscala.collection.mutable- Mutable, sequential data-structures such asArrayBuffer,StringBuilder,HashMaporHashSetscala.collection.concurrent- Mutable, concurrent data-structures such asTrieMapscala.concurrent- Primitives for concurrent programming such asFuturesandPromisesscala.io- Input and output operationsscala.math- Basic math functions and additional numeric types likeBigIntandBigDecimalscala.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.Predefobject are always in scope by default.Some of these identifiers are type aliases provided as shortcuts to commonly used classes. For example,
Listis an alias forscala.collection.immutable.List.Other aliases refer to classes provided by the underlying platform. For example, on the JVM,
Stringis an alias forjava.lang.String.