Scala Standard Library2.13.15 < Back
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# Packages

-  package root

  This is the documentation for the Scala standard library.

  This is the documentation for the Scala standard library.

  #### Package structure

  The scala package contains core types like `Int`, `Float`, `Array` or `Option` 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 framework
    - `scala.collection.immutable` - Immutable, sequential data-structures such as `Vector`, `List`, `Range`, `HashMap` or `HashSet`
    - `scala.collection.mutable` - Mutable, sequential data-structures such as `ArrayBuffer`, `StringBuilder`, `HashMap` or `HashSet`
    - `scala.collection.concurrent` - Mutable, concurrent data-structures such as `TrieMap`
  - `scala.concurrent` - Primitives for concurrent programming such as `Futures` and `Promises`
  - `scala.io` - Input and output operations
  - `scala.math` - Basic math functions and additional numeric types like `BigInt` and `BigDecimal`
  - `scala.sys` - Interaction with other processes and the operating system
  - `scala.util.matching` - Regular expressions

  Other 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 for `scala.collection.immutable.List`.

  Other aliases refer to classes provided by the underlying platform. For example, on the JVM, `String` is an alias for `java.lang.String`.

  Definition Classes
    root
-  package scala

  Core Scala types.

  Core Scala types. They are always available without an explicit import.

  Definition Classes
    root
-  package jdk

  The jdk package contains utilities to interact with JDK classes.

  The jdk package contains utilities to interact with JDK classes.

  This packages offers a number of converters, that are able to wrap or copy types from the scala library to equivalent types in the JDK class library and vice versa:

  - CollectionConverters, converting collections like scala.collection.Seq, scala.collection.Map, scala.collection.Set, scala.collection.mutable.Buffer, scala.collection.Iterator and scala.collection.Iterable to their JDK counterparts
  - OptionConverters, converting between Option and java.util.Optional and primitive variations
  - StreamConverters, to create JDK Streams from scala collections
  - DurationConverters, for conversions between scala scala.concurrent.duration.FiniteDuration and java.time.Duration
  - FunctionConverters, from scala Functions to java java.util.function.Function, java.util.function.UnaryOperator, java.util.function.Consumer and java.util.function.Predicate, as well as primitive variations and Bi-variations.

  By convention, converters that wrap an object to provide a different interface to the same underlying data structure use .asScala and .asJava extension methods, whereas converters that copy the underlying data structure use .toScala and .toJava.

  In the javaapi package, the same converters can be found with a java-friendly interface that don't rely on implicit enrichments.

  Additionally, this package offers Accumulators, capable of efficiently traversing JDK Streams.

  Definition Classes
    scala
-  package javaapi
  Definition Classes
    jdk
- Accumulator
- AnyAccumulator
- CollectionConverters
- DoubleAccumulator
- DurationConverters
- FunctionConverters
- FunctionWrappers
- FutureConverters
- IntAccumulator
- LongAccumulator
- OptionConverters
- OptionShape
- Priority0FunctionExtensions
- Priority1FunctionExtensions
- Priority2FunctionExtensions
- Priority3FunctionExtensions
- StreamConverters

o

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 = 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.

Source
  StreamConverters.scala

Linear Supertypes
StreamExtensions, AnyRef, Any
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2. StreamExtensions
3. AnyRef
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Visibility

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2. Protected

### 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, Map, _]] extends AnyRef
    Definition Classes
      StreamExtensions
14.  implicit class MapHasSeqKeyValueStream[K, V, CC[X, Y] <: MapOps[X, Y, Map, _]] 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

### 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

   Forces the compiler to treat the receiver object as having type `T0`, even though doing so may violate type safety.

   Forces the compiler to treat the receiver object as having type `T0`, even though doing so may violate type safety.

   This method is useful when you believe you have type information the compiler doesn't, and it also isn't possible to check the type at runtime. In such situations, skipping type safety is the only option.

   It is platform dependent whether `asInstanceOf` has any effect at runtime. It might do a runtime type test on the erasure of `T0`, insert a conversion (such as boxing/unboxing), fill in a default value, or do nothing at all.

   In particular, `asInstanceOf` is not a type test. It does **not** mean:

       this match {
        case x: T0 => x
        case _     => throw ClassCastException("...")

   Use pattern matching or isInstanceOf for type testing instead.

   Situations where `asInstanceOf` is useful:

   - when flow analysis fails to deduce `T0` automatically
   - when down-casting a type parameter or an abstract type member (which cannot be checked at runtime due to type erasure) If there is any doubt and you are able to type test instead, you should do so.

   Be careful of using `asInstanceOf` when `T0` is a primitive type. When `T0` is primitive, `asInstanceOf` may insert a conversion instead of a type test. If your intent is to convert, use a `toT` method (`x.toChar`, `x.toByte`, etc.).

   returns

     the receiver object.

   Definition Classes
     Any
   Exceptions thrown

     `ClassCastException` if the receiver is not an instance of the erasure of `T0`, if that can be checked on this platform

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[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[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 has the same erasure as `T0`.

    Test whether the dynamic type of the receiver object has the same erasure as `T0`.

    Depending on what `T0` is, the test is done in one of the below ways:

    - `T0` is a non-parameterized class type, e.g. `BigDecimal`: this method returns `true` if the value of the receiver object is a `BigDecimal` or a subtype of `BigDecimal`.
    - `T0` is a parameterized class type, e.g. `List[Int]`: this method returns `true` if the value of the receiver object is some `List[X]` for any `X`. For example, `List(1, 2, 3).isInstanceOf[List[String]]` will return true.
    - `T0` is some singleton type `x.type` or literal `x`: this method returns `this.eq(x)`. For example, `x.isInstanceOf[1]` is equivalent to `x.eq(1)`
    - `T0` is an intersection `X with Y` or `X & Y: this method is equivalent to` x.isInstanceOf[X] && x.isInstanceOf[Y]``
    - `T0` is a union `X | Y`: this method is equivalent to `x.isInstanceOf[X] || x.isInstanceOf[Y]`
    - `T0` is a type parameter or an abstract type member: this method is equivalent to `isInstanceOf[U]` where `U` is `T0`'s upper bound, `Any` if `T0` is unbounded. For example, `x.isInstanceOf[A]` where `A` is an unbounded type parameter will return true for any value of `x`.

    This is exactly equivalent to the type pattern `_: T0`

    returns

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

    Definition Classes
      Any
    Note

      due to the unexpectedness of `List(1, 2, 3).isInstanceOf[List[String]]` returning true and `x.isInstanceOf[A]` where `A` is a type parameter or abstract member returning true, these forms issue a warning.

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

    Executes the code in `body` with an exclusive lock on `this`.

    Executes the code in `body` with an exclusive lock on `this`.

    returns

      the result of `body`

    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

    See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait--.

    See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait--.

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

      not specified by SLS as a member of AnyRef

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

    See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-int-

    See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-int-

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

      not specified by SLS as a member of AnyRef

19.  final def wait(arg0: Long): Unit

    See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-.

    See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-.

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

      not specified by SLS as a member of AnyRef

### Inherited from StreamExtensions

### Inherited from AnyRef

### Inherited from Any

### Ungrouped