Scala Standard Library2.13.0 < 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 annotation
  Definition Classes
    scala
-  package beans
  Definition Classes
    scala
-  package collection
  Definition Classes
    scala
-  package compat
  Definition Classes
    scala
-  package concurrent

  This package object contains primitives for concurrent and parallel programming.

  This package object contains primitives for concurrent and parallel programming.

  #### Guide

  A more detailed guide to Futures and Promises, including discussion and examples can be found at http://docs.scala-lang.org/overviews/core/futures.html.

  #### Common Imports

  When working with Futures, you will often find that importing the whole concurrent package is convenient:

      import scala.concurrent._

  When using things like `Future`s, it is often required to have an implicit `ExecutionContext` in scope. The general advice for these implicits are as follows.

  If the code in question is a class or method definition, and no `ExecutionContext` is available, request one from the caller by adding an implicit parameter list:

      def myMethod(myParam: MyType)(implicit ec: ExecutionContext) = …
      //Or
      class MyClass(myParam: MyType)(implicit ec: ExecutionContext) { … }

  This allows the caller of the method, or creator of the instance of the class, to decide which `ExecutionContext` should be used.

  For typical REPL usage and experimentation, importing the global `ExecutionContext` is often desired.

      import scala.concurrent.ExcutionContext.Implicits.global

  #### Specifying Durations

  Operations often require a duration to be specified. A duration DSL is available to make defining these easier:

      import scala.concurrent.duration._
      val d: Duration = 10.seconds

  #### Using Futures For Non-blocking Computation

  Basic use of futures is easy with the factory method on Future, which executes a provided function asynchronously, handing you back a future result of that function without blocking the current thread. In order to create the Future you will need either an implicit or explicit ExecutionContext to be provided:

      import scala.concurrent._
      import ExecutionContext.Implicits.global  // implicit execution context

      val firstZebra: Future[Int] = Future {
        val source = scala.io.Source.fromFile("/etc/dictionaries-common/words")
        source.toSeq.indexOfSlice("zebra")
      }

  #### Avoid Blocking

  Although blocking is possible in order to await results (with a mandatory timeout duration):

      import scala.concurrent.duration._
      Await.result(firstZebra, 10.seconds)

  and although this is sometimes necessary to do, in particular for testing purposes, blocking in general is discouraged when working with Futures and concurrency in order to avoid potential deadlocks and improve performance. Instead, use callbacks or combinators to remain in the future domain:

      val animalRange: Future[Int] = for {
        aardvark <- firstAardvark
        zebra <- firstZebra
      } yield zebra - aardvark

      animalRange.onSuccess {
        case x if x > 500000 => println("It's a long way from Aardvark to Zebra")
      }

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

  The package object `scala.math` contains methods for performing basic numeric operations such as elementary exponential, logarithmic, root and trigonometric functions.

  The package object `scala.math` contains methods for performing basic numeric operations such as elementary exponential, logarithmic, root and trigonometric functions.

  All methods forward to java.lang.Math unless otherwise noted.

  Definition Classes
    scala
  See also

    java.lang.Math

-  package ref
  Definition Classes
    scala
-  package reflect
  Definition Classes
    scala
-  package sys

  The package object `scala.sys` contains methods for reading and altering core aspects of the virtual machine as well as the world outside of it.

  The package object `scala.sys` contains methods for reading and altering core aspects of the virtual machine as well as the world outside of it.

  Definition Classes
    scala
  Since

    2.9

-  package util
  Definition Classes
    scala

p

scala

# jdk

#### package jdk

Content Hierarchy
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Ordering

1. Alphabetic

Visibility

1. Public
2. All

### Package Members

1.  package javaapi

### Type Members

1.  abstract class Accumulator[A, +CC[X] <: collection.mutable.Seq[X], +C <: collection.mutable.Seq[A]] extends collection.mutable.Seq[A] with Builder[A, C]

   Accumulators are mutable sequences with two distinct features:

   Accumulators are mutable sequences with two distinct features:

   - An accumulator can be appended efficiently to another
   - There are manually specialized Accumulators for `Int`, `Long` and `Double` that don't box the elements

   These two features make Accumulators a good candidate to collect the results of a parallel Java stream pipeline into a Scala collection. The scala.collection.convert.StreamExtensions.StreamHasToScala.toScala extension method on Java streams (available by importing `scala.jdk.StreamConverters._`) is specialized for Accumulators: they are built in parallel, the parts are merged efficiently.

   Building specialized Accumulators is handled transparently. As a user, using the Accumulator object as a factory automatically creates an IntAccumulator, LongAccumulator, DoubleAccumulator or AnyAccumulator depending on the element type.

   Note: to run the example, start the Scala REPL with `scala -Yrepl-class-based` to avoid deadlocks, see https://github.com/scala/bug/issues/9076.

       scala> import scala.jdk.StreamConverters._
       import scala.jdk.StreamConverters._

       scala> def isPrime(n: Int): Boolean = !(2 +: (3 to Math.sqrt(n).toInt by 2) exists (n % _ == 0))
       isPrime: (n: Int)Boolean

       scala> val intAcc = (1 to 10000).asJavaParStream.filter(isPrime).toScala(scala.jdk.Accumulator)
       intAcc: scala.jdk.IntAccumulator = IntAccumulator(1, 3, 5, 7, 11, 13, 17, 19, ...

       scala> val stringAcc = (1 to 100).asJavaParStream.mapToObj("<>" * _).toScala(Accumulator)
       stringAcc: scala.jdk.AnyAccumulator[String] = AnyAccumulator(<>, <><>, <><><>, ...

   There are two possibilities to process elements of a primitive Accumulator without boxing: specialized operations of the Accumulator, or the Stepper interface. The most common collection operations are overloaded or overridden in the primitive Accumulator classes, for example IntAccumulator.map or IntAccumulator.exists. Thanks to Scala's function specialization, `intAcc.exists(x => testOn(x))` does not incur boxing.

   The Stepper interface provides iterator-like `hasStep` and `nextStep` methods, and is specialized for `Int`, `Long` and `Double`. The `intAccumulator.stepper` method creates an scala.collection.IntStepper that yields the elements of the accumulator without boxing.

   Accumulators can hold more than `Int.MaxValue` elements. They have a sizeLong method that returns the size as a `Long`. Note that certain operations defined in scala.collection.Seq are implemented using length, so they will not work correctly for large accumulators.

   The Accumulator class is a base class to share code between AnyAccumulator (for reference types) and the manual specializations IntAccumulator, LongAccumulator and DoubleAccumulator.

2.  final class AnyAccumulator[A] extends Accumulator[A, AnyAccumulator, AnyAccumulator[A]] with SeqOps[A, AnyAccumulator, AnyAccumulator[A]] with IterableFactoryDefaults[A, AnyAccumulator] with Serializable

   An Accumulator for arbitrary element types, see Accumulator.

3.  final class DoubleAccumulator extends Accumulator[Double, AnyAccumulator, DoubleAccumulator] with SeqOps[Double, AnyAccumulator, DoubleAccumulator] with Serializable

   A specialized Accumulator that holds `Double`s without boxing, see Accumulator.

4.  final class IntAccumulator extends Accumulator[Int, AnyAccumulator, IntAccumulator] with SeqOps[Int, AnyAccumulator, IntAccumulator] with Serializable

   A specialized Accumulator that holds `Int`s without boxing, see Accumulator.

5.  final class LongAccumulator extends Accumulator[Long, AnyAccumulator, LongAccumulator] with SeqOps[Long, AnyAccumulator, LongAccumulator] with Serializable

   A specialized Accumulator that holds `Long`s without boxing, see Accumulator.

6.  sealed abstract class OptionShape[A, O] extends AnyRef

   A type class implementing conversions from a generic Scala `Option` or Java `Optional` to a specialized Java variant (for `Double`, `Int` and `Long`).

   A type class implementing conversions from a generic Scala `Option` or Java `Optional` to a specialized Java variant (for `Double`, `Int` and `Long`).

   A

     the primitive type wrapped in an option

   O

     the specialized Java `Optional` wrapping an element of type `A`

   Annotations
     @implicitNotFound("No specialized Optional type exists for elements of type ${A}")
7.  trait Priority0FunctionExtensions extends Priority1FunctionExtensions
8.  trait Priority1FunctionExtensions extends Priority2FunctionExtensions
9.  trait Priority2FunctionExtensions extends Priority3FunctionExtensions
10.  trait Priority3FunctionExtensions extends AnyRef

### Value Members

1.  object Accumulator

   Contains factory methods to build Accumulators.

   Contains factory methods to build Accumulators.

   Note that the `Accumulator` object itself is not a factory, but it is implicitly convert to a factory according to the element type, see Accumulator.toFactory.

   This allows passing the `Accumulator` object as argument when a collection.Factory, and the implicit Accumulator.AccumulatorFactoryShape instance is used to build a specialized Accumulator according to the element type:

       scala> val intAcc = Accumulator(1,2,3)
       intAcc: scala.collection.convert.IntAccumulator = IntAccumulator(1, 2, 3)

       scala> val anyAccc = Accumulator("K")
       anyAccc: scala.collection.convert.AnyAccumulator[String] = AnyAccumulator(K)

       scala> val intAcc2 = List(1,2,3).to(Accumulator)
       intAcc2: scala.jdk.IntAccumulator = IntAccumulator(1, 2, 3)

       scala> val anyAcc2 = List("K").to(Accumulator)
       anyAcc2: scala.jdk.AnyAccumulator[String] = AnyAccumulator(K)

2.  object AnyAccumulator extends SeqFactory[AnyAccumulator]
3.  object CollectionConverters extends AsJavaExtensions with AsScalaExtensions

   This object provides extension methods that convert between Scala and Java collections.

   This object provides extension methods that convert between Scala and Java collections.

   When writing Java code, use the explicit conversion methods defined in javaapi.CollectionConverters instead.

   Note: to create Java Streams that operate on Scala collections (sequentially or in parallel), use StreamConverters.

       import scala.jdk.CollectionConverters._
       val s: java.util.Set[String] = Set("one", "two").asJava

   The conversions return adapters for the corresponding API, i.e., the collections are wrapped, not converted. Changes to the original collection are reflected in the view, and vice versa:

       scala> import scala.jdk.CollectionConverters._

       scala> val s = collection.mutable.Set("one")
       s: scala.collection.mutable.Set[String] = HashSet(one)

       scala> val js = s.asJava
       js: java.util.Set[String] = [one]

       scala> js.add("two")

       scala> s
       res2: scala.collection.mutable.Set[String] = HashSet(two, one)

   The following conversions are supported via `asScala` and `asJava`:

       scala.collection.Iterable       <=> java.lang.Iterable
       scala.collection.Iterator       <=> java.util.Iterator
       scala.collection.mutable.Buffer <=> java.util.List
       scala.collection.mutable.Set    <=> java.util.Set
       scala.collection.mutable.Map    <=> java.util.Map
       scala.collection.concurrent.Map <=> java.util.concurrent.ConcurrentMap

   The following conversions are supported via `asScala` and through specially-named extension methods to convert to Java collections, as shown:

       scala.collection.Iterable    <=> java.util.Collection   (via asJavaCollection)
       scala.collection.Iterator    <=> java.util.Enumeration  (via asJavaEnumeration)
       scala.collection.mutable.Map <=> java.util.Dictionary   (via asJavaDictionary)

   In addition, the following one-way conversions are provided via `asJava`:

       scala.collection.Seq         => java.util.List
       scala.collection.mutable.Seq => java.util.List
       scala.collection.Set         => java.util.Set
       scala.collection.Map         => java.util.Map

   The following one way conversion is provided via `asScala`:

       java.util.Properties => scala.collection.mutable.Map

   In all cases, converting from a source type to a target type and back again will return the original source object. For example:

       import scala.jdk.CollectionConverters._

       val source = new scala.collection.mutable.ListBuffer[Int]
       val target: java.util.List[Int] = source.asJava
       val other: scala.collection.mutable.Buffer[Int] = target.asScala
       assert(source eq other)

4.  object DoubleAccumulator extends SpecificIterableFactory[Double, DoubleAccumulator] with java.io.Serializable
5.  object DurationConverters

   This object provides extension methods that convert between Scala and Java duration types.

   This object provides extension methods that convert between Scala and Java duration types.

   When writing Java code, use the explicit conversion methods defined in javaapi.DurationConverters instead.

6.  object FunctionConverters extends Priority0FunctionExtensions

   This object provides extension methods that convert between Scala and Java function types.

   This object provides extension methods that convert between Scala and Java function types.

   When writing Java code, use the explicit conversion methods defined in javaapi.FunctionConverters instead.

   Using the `.asJava` extension method on a Scala function produces the most specific possible Java function type:

       scala> import scala.jdk.FunctionConverters._
       scala> val f = (x: Int) => x + 1

       scala> val jf1 = f.asJava
       jf1: java.util.function.IntUnaryOperator = ...

   More generic Java function types can be created using the corresponding `asJavaXYZ` extension method:

       scala> val jf2 = f.asJavaFunction
       jf2: java.util.function.Function[Int,Int] = ...

       scala> val jf3 = f.asJavaUnaryOperator
       jf3: java.util.function.UnaryOperator[Int] = ...

   Converting a Java function to Scala is done using the `asScala` extension method:

       scala> List(1,2,3).map(jf2.asScala)
       res1: List[Int] = List(2, 3, 4)

7.  object FunctionWrappers
8.  object FutureConverters

   This object provides extension methods that convert between Scala Future and Java CompletionStage

   This object provides extension methods that convert between Scala Future and Java CompletionStage

   When writing Java code, use the explicit conversion methods defined in javaapi.FutureConverters instead.

   Note that the bridge is implemented at the read-only side of asynchronous handles, namely Future (instead of scala.concurrent.Promise) and CompletionStage (instead of java.util.concurrent.CompletableFuture). This is intentional, as the semantics of bridging the write-handles would be prone to race conditions; if both ends (`CompletableFuture` and `Promise`) are completed independently at the same time, they may contain different values afterwards. For this reason, `toCompletableFuture` is not supported on the created `CompletionStage`s.

9.  object IntAccumulator extends SpecificIterableFactory[Int, IntAccumulator] with java.io.Serializable
10.  object LongAccumulator extends SpecificIterableFactory[Long, LongAccumulator] with java.io.Serializable
11.  object OptionConverters

    This object provides extension methods that convert between Scala `Option` and Java `Optional` types.

    This object provides extension methods that convert between Scala `Option` and Java `Optional` types.

    When writing Java code, use the explicit conversion methods defined in javaapi.OptionConverters instead.

    Scala `Option` is extended with a `toJava` method that creates a corresponding `Optional`, and a `toJavaPrimitive` method that creates a specialized variant (e.g., `OptionalInt`) if applicable.

    Java `Optional` is extended with a `toScala` method and a `toJavaPrimitive` method.

    Finally, specialized `Optional` types are extended with `toScala` and `toJavaGeneric` methods.

    Example usage:

        import scala.jdk.OptionConverters._
        val a = Option("example").toJava      // Creates java.util.Optional[String] containing "example"
        val b = (None: Option[String]).toJava // Creates an empty java.util.Optional[String]
        val c = a.toScala                     // Back to Option("example")
        val d = b.toScala                     // Back to None typed as Option[String]
        val e = Option(2.7).toJava            // java.util.Optional[Double] containing boxed 2.7
        val f = Option(2.7).toJavaPrimitive   // java.util.OptionalDouble containing 2.7 (not boxed)
        val g = f.toScala                     // Back to Option(2.7)
        val h = f.toJavaGeneric               // Same as e
        val i = e.toJavaPrimitive             // Same as f

12.  object OptionShape
13.  object StreamConverters extends StreamExtensions

    This object provides extension methods to create Java Streams that operate on Scala collections (sequentially or in parallel).

    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.

### Ungrouped