java8.util.stream

Class StreamSupport

java.lang.Object

java8.util.stream.StreamSupport

public final class StreamSupport
extends java.lang.Object

Low-level utility methods for creating and manipulating streams.

This class is mostly for library writers presenting stream views of data structures; most static stream methods intended for end users are in the various Stream classes.

Since:

1.8

Method Summary

Modifier and Type	Method and Description
static <T> Stream.Builder<T>	add(Stream.Builder<T> builder, T t) Adds an element to the stream being built represented by the Stream.Builder argument.
static <T> Stream.Builder<T>	builder() Returns a builder for a Stream.
static <T> Stream<T>	concat(Stream<? extends T> a, Stream<? extends T> b) Creates a lazily concatenated stream whose elements are all the elements of the first stream followed by all the elements of the second stream.
static DoubleStream	doubleStream(Spliterator.OfDouble spliterator, boolean parallel) Creates a new sequential or parallel DoubleStream from a Spliterator.OfDouble.
static DoubleStream	doubleStream(Supplier<? extends Spliterator.OfDouble> supplier, int characteristics, boolean parallel) Creates a new sequential or parallel DoubleStream from a Supplier of Spliterator.OfDouble.
static <T> Stream<T>	empty() Returns an empty sequential Stream.
static <T> Stream<T>	generate(Supplier<T> s) Returns an infinite sequential unordered stream where each element is generated by the provided Supplier.
static IntStream	intStream(Spliterator.OfInt spliterator, boolean parallel) Creates a new sequential or parallel IntStream from a Spliterator.OfInt.
static IntStream	intStream(Supplier<? extends Spliterator.OfInt> supplier, int characteristics, boolean parallel) Creates a new sequential or parallel IntStream from a Supplier of Spliterator.OfInt.
static <T> Stream<T>	iterate(T seed, UnaryOperator<T> f) Returns an infinite sequential ordered Stream produced by iterative application of a function f to an initial element seed, producing a Stream consisting of seed, f(seed), f(f(seed)), etc.
static LongStream	longStream(Spliterator.OfLong spliterator, boolean parallel) Creates a new sequential or parallel LongStream from a Spliterator.OfLong.
static LongStream	longStream(Supplier<? extends Spliterator.OfLong> supplier, int characteristics, boolean parallel) Creates a new sequential or parallel LongStream from a Supplier of Spliterator.OfLong.
static <T> Stream<T>	of(T... values) Returns a sequential ordered stream whose elements are the specified values.
static <T> Stream<T>	of(T t) Returns a sequential Stream containing a single element.
static <T> Stream<T>	parallelStream(java.util.Collection<? extends T> c) Creates a new possibly parallel Stream using either the given collection's Collection.iterator() as the source of elements for an internally created Spliterator which will report the collection's Collection.size() as its initial size or a specialized Spliterator implementation (effectively the same one that Java 8 uses) if the passed Collection is one of the types listed below.
static <T> Stream<T>	stream(java.util.Collection<? extends T> c) Creates a new sequential Stream using either the given collection's Collection.iterator() as the source of elements for an internally created Spliterator which will report the collection's Collection.size() as its initial size or a specialized Spliterator implementation (effectively the same one that Java 8 uses) if the passed Collection is one of the types listed below.
static <T> Stream<T>	stream(java.util.Collection<? extends T> c, int characteristics) Creates a new sequential Stream using the given collection's Collection.iterator() as the source of elements for an internally created Spliterator which will report the collection's Collection.size() as its initial size.
static <T> Stream<T>	stream(java.util.Collection<? extends T> c, int characteristics, boolean parallel) Creates a new sequential or parallel Stream using the given collection's Collection.iterator() as the source of elements for an internally created Spliterator which will report the collection's Collection.size() as its initial size.
static <T> Stream<T>	stream(Spliterator<T> spliterator, boolean parallel) Creates a new sequential or parallel Stream from a Spliterator.
static <T> Stream<T>	stream(Supplier<? extends Spliterator<T>> supplier, int characteristics, boolean parallel) Creates a new sequential or parallel Stream from a Supplier of Spliterator.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

builder

public static <T> Stream.Builder<T> builder()

Returns a builder for a Stream.

Type Parameters:

T - type of elements

Returns:

a stream builder

empty

public static <T> Stream<T> empty()

Returns an empty sequential Stream.

Type Parameters:

T - the type of stream elements

Returns:

an empty sequential stream

of

public static <T> Stream<T> of(T t)

Returns a sequential Stream containing a single element.

Type Parameters:

T - the type of stream elements

Parameters:

t - the single element

Returns:

a singleton sequential stream

of

public static <T> Stream<T> of(T... values)

Returns a sequential ordered stream whose elements are the specified values.

Type Parameters:

T - the type of stream elements

Parameters:

values - the elements of the new stream

Returns:

the new stream

iterate

public static <T> Stream<T> iterate(T seed,
                                    UnaryOperator<T> f)

Returns an infinite sequential ordered Stream produced by iterative application of a function f to an initial element seed, producing a Stream consisting of seed, f(seed), f(f(seed)), etc.

The first element (position 0) in the Stream will be the provided seed. For n > 0, the element at position n, will be the result of applying the function f to the element at position n - 1.

Type Parameters:

T - the type of stream elements

Parameters:

seed - the initial element

f - a function to be applied to to the previous element to produce a new element

Returns:

a new sequential Stream

generate

public static <T> Stream<T> generate(Supplier<T> s)

Returns an infinite sequential unordered stream where each element is generated by the provided Supplier. This is suitable for generating constant streams, streams of random elements, etc.

Type Parameters:

T - the type of stream elements

Parameters:

s - the Supplier of generated elements

Returns:

a new infinite sequential unordered Stream

concat

public static <T> Stream<T> concat(Stream<? extends T> a,
                                   Stream<? extends T> b)

Creates a lazily concatenated stream whose elements are all the elements of the first stream followed by all the elements of the second stream. The resulting stream is ordered if both of the input streams are ordered, and parallel if either of the input streams is parallel. When the resulting stream is closed, the close handlers for both input streams are invoked.

Implementation Note:
Use caution when constructing streams from repeated concatenation. Accessing an element of a deeply concatenated stream can result in deep call chains, or even StackOverflowException.

Type Parameters:

T - The type of stream elements

Parameters:

a - the first stream

b - the second stream

Returns:

the concatenation of the two input streams

add

public static <T> Stream.Builder<T> add(Stream.Builder<T> builder,
                                        T t)

Adds an element to the stream being built represented by the Stream.Builder argument.

Implementation Requirements:
The default implementation behaves as if:

     builder.accept(t)
     return builder;
 

Type Parameters:

T - the type of stream elements

Parameters:

builder - the Stream.Builder to use

t - the element to add

Returns:

the passed builder

Throws:

java.lang.IllegalStateException - if the builder has already transitioned to the built state

stream

public static <T> Stream<T> stream(java.util.Collection<? extends T> c)

Creates a new sequential Stream using either the given collection's Collection.iterator() as the source of elements for an internally created Spliterator which will report the collection's Collection.size() as its initial size or a specialized Spliterator implementation (effectively the same one that Java 8 uses) if the passed Collection is one of the types listed below.

• java.util.ArrayList
• java.util.Arrays.ArrayList
• java.util.ArrayDeque
• java.util.Vector
• java.util.LinkedHashSet
• java.util.PriorityQueue
• java.util.concurrent.ArrayBlockingQueue
• java.util.concurrent.PriorityBlockingQueue
• java.util.concurrent.CopyOnWriteArrayList
• java.util.concurrent.CopyOnWriteArraySet

The Spliterators for CopyOnWriteArrayList and CopyOnWriteArraySet provide a snapshot of the state of the collection when the Stream was created, otherwise the created spliterator is late-binding, inherits the fail-fast properties of the collection's iterator, and implements trySplit to permit limited parallelism.

The created spliterator is only traversed, split, or queried for estimated size after the terminal operation of the stream pipeline commences.

Type Parameters:

T - Type of elements

Parameters:

c - The collection

Returns:

a new sequential Stream

Throws:

java.lang.NullPointerException - if the given collection is null

parallelStream

public static <T> Stream<T> parallelStream(java.util.Collection<? extends T> c)

Creates a new possibly parallel Stream using either the given collection's Collection.iterator() as the source of elements for an internally created Spliterator which will report the collection's Collection.size() as its initial size or a specialized Spliterator implementation (effectively the same one that Java 8 uses) if the passed Collection is one of the types listed below.

• java.util.ArrayList
• java.util.Arrays.ArrayList
• java.util.ArrayDeque
• java.util.Vector
• java.util.LinkedHashSet
• java.util.PriorityQueue
• java.util.concurrent.ArrayBlockingQueue
• java.util.concurrent.PriorityBlockingQueue
• java.util.concurrent.CopyOnWriteArrayList
• java.util.concurrent.CopyOnWriteArraySet

The Spliterators for CopyOnWriteArrayList and CopyOnWriteArraySet provide a snapshot of the state of the collection when the Stream was created, otherwise the created spliterator is late-binding, inherits the fail-fast properties of the collection's iterator, and implements trySplit to permit limited parallelism.

The created spliterator is only traversed, split, or queried for estimated size after the terminal operation of the stream pipeline commences.

Type Parameters:

T - Type of elements

Parameters:

c - The collection

Returns:

a new possibly parallel Stream

Throws:

java.lang.NullPointerException - if the given collection is null

stream

public static <T> Stream<T> stream(java.util.Collection<? extends T> c,
                                   int characteristics)

Creates a new sequential Stream using the given collection's Collection.iterator() as the source of elements for an internally created Spliterator which will report the collection's Collection.size() as its initial size.

The created spliterator is late-binding, inherits the fail-fast properties of the collection's iterator, and implements trySplit to permit limited parallelism.

The created spliterator is only traversed, split, or queried for estimated size after the terminal operation of the stream pipeline commences.

If the collection is immutable it is recommended to report a characteristic of IMMUTABLE. The characteristics SIZED and SUBSIZED are additionally (automatically) reported unless CONCURRENT is supplied.

Type Parameters:

T - Type of elements

Parameters:

c - The collection

characteristics - Characteristics of the source collection's iterator or elements. The characteristics SIZED and SUBSIZED are additionally reported unless CONCURRENT is supplied.

Returns:

a new sequential Stream

Throws:

java.lang.NullPointerException - if the given collection is null

stream

public static <T> Stream<T> stream(java.util.Collection<? extends T> c,
                                   int characteristics,
                                   boolean parallel)

Creates a new sequential or parallel Stream using the given collection's Collection.iterator() as the source of elements for an internally created Spliterator which will report the collection's Collection.size() as its initial size.

The created spliterator is late-binding, inherits the fail-fast properties of the collection's iterator, and implements trySplit to permit limited parallelism.

The created spliterator is only traversed, split, or queried for estimated size after the terminal operation of the stream pipeline commences.

If possible for the collection, it is strongly recommended to report a characteristic of IMMUTABLE or CONCURRENT especially if you want a parallel Stream. The characteristics SIZED and SUBSIZED are additionally (automatically) reported unless CONCURRENT is supplied.

Type Parameters:

T - Type of elements

Parameters:

c - The collection

characteristics - Characteristics of the source collection's iterator or elements. The characteristics SIZED and SUBSIZED are additionally reported unless CONCURRENT is supplied.

parallel - if true then the returned stream is a parallel stream; if false the returned stream is a sequential stream.

Returns:

a new sequential or parallel Stream

Throws:

java.lang.NullPointerException - if the given collection is null

stream

public static <T> Stream<T> stream(Spliterator<T> spliterator,
                                   boolean parallel)

Creates a new sequential or parallel Stream from a Spliterator.

The spliterator is only traversed, split, or queried for estimated size after the terminal operation of the stream pipeline commences.

It is strongly recommended the spliterator report a characteristic of IMMUTABLE or CONCURRENT, or be late-binding. Otherwise, stream(java8.util.function.Supplier, int, boolean) should be used to reduce the scope of potential interference with the source. See Non-Interference for more details.

Type Parameters:

T - the type of stream elements

Parameters:

spliterator - a Spliterator describing the stream elements

parallel - if true then the returned stream is a parallel stream; if false the returned stream is a sequential stream.

Returns:

a new sequential or parallel Stream

stream

public static <T> Stream<T> stream(Supplier<? extends Spliterator<T>> supplier,
                                   int characteristics,
                                   boolean parallel)

Creates a new sequential or parallel Stream from a Supplier of Spliterator.

The Supplier.get() method will be invoked on the supplier no more than once, and only after the terminal operation of the stream pipeline commences.

For spliterators that report a characteristic of IMMUTABLE or CONCURRENT, or that are late-binding, it is likely more efficient to use stream(java8.util.Spliterator, boolean) instead.

The use of a Supplier in this form provides a level of indirection that reduces the scope of potential interference with the source. Since the supplier is only invoked after the terminal operation commences, any modifications to the source up to the start of the terminal operation are reflected in the stream result. See Non-Interference for more details.

Type Parameters:

T - the type of stream elements

Parameters:

supplier - a Supplier of a Spliterator

characteristics - Spliterator characteristics of the supplied Spliterator. The characteristics must be equal to supplier.get().characteristics(), otherwise undefined behavior may occur when terminal operation commences.

parallel - if true then the returned stream is a parallel stream; if false the returned stream is a sequential stream.

Returns:

a new sequential or parallel Stream

See Also:

stream(java8.util.Spliterator, boolean)

intStream

public static IntStream intStream(Spliterator.OfInt spliterator,
                                  boolean parallel)

Creates a new sequential or parallel IntStream from a Spliterator.OfInt.

The spliterator is only traversed, split, or queried for estimated size after the terminal operation of the stream pipeline commences.

It is strongly recommended the spliterator report a characteristic of IMMUTABLE or CONCURRENT, or be late-binding. Otherwise, intStream(java8.util.function.Supplier, int, boolean) should be used to reduce the scope of potential interference with the source. See Non-Interference for more details.

Parameters:

spliterator - a Spliterator.OfInt describing the stream elements

parallel - if true then the returned stream is a parallel stream; if false the returned stream is a sequential stream.

Returns:

a new sequential or parallel IntStream

intStream

public static IntStream intStream(Supplier<? extends Spliterator.OfInt> supplier,
                                  int characteristics,
                                  boolean parallel)

Creates a new sequential or parallel IntStream from a Supplier of Spliterator.OfInt.

The Supplier.get() method will be invoked on the supplier no more than once, and only after the terminal operation of the stream pipeline commences.

For spliterators that report a characteristic of IMMUTABLE or CONCURRENT, or that are late-binding, it is likely more efficient to use intStream(java8.util.Spliterator.OfInt, boolean) instead.

The use of a Supplier in this form provides a level of indirection that reduces the scope of potential interference with the source. Since the supplier is only invoked after the terminal operation commences, any modifications to the source up to the start of the terminal operation are reflected in the stream result. See Non-Interference for more details.

Parameters:

supplier - a Supplier of a Spliterator.OfInt

characteristics - Spliterator characteristics of the supplied Spliterator.OfInt. The characteristics must be equal to supplier.get().characteristics(), otherwise undefined behavior may occur when terminal operation commences.

parallel - if true then the returned stream is a parallel stream; if false the returned stream is a sequential stream.

Returns:

a new sequential or parallel IntStream

See Also:

intStream(java8.util.Spliterator.OfInt, boolean)

longStream

public static LongStream longStream(Spliterator.OfLong spliterator,
                                    boolean parallel)

Creates a new sequential or parallel LongStream from a Spliterator.OfLong.

The spliterator is only traversed, split, or queried for estimated size after the terminal operation of the stream pipeline commences.

It is strongly recommended the spliterator report a characteristic of IMMUTABLE or CONCURRENT, or be late-binding. Otherwise, longStream(java8.util.function.Supplier, int, boolean) should be used to reduce the scope of potential interference with the source. See Non-Interference for more details.

Parameters:

spliterator - a Spliterator.OfLong describing the stream elements

parallel - if true then the returned stream is a parallel stream; if false the returned stream is a sequential stream.

Returns:

a new sequential or parallel LongStream

longStream

public static LongStream longStream(Supplier<? extends Spliterator.OfLong> supplier,
                                    int characteristics,
                                    boolean parallel)

Creates a new sequential or parallel LongStream from a Supplier of Spliterator.OfLong.

The Supplier.get() method will be invoked on the supplier no more than once, and only after the terminal operation of the stream pipeline commences.

For spliterators that report a characteristic of IMMUTABLE or CONCURRENT, or that are late-binding, it is likely more efficient to use longStream(java8.util.Spliterator.OfLong, boolean) instead.

The use of a Supplier in this form provides a level of indirection that reduces the scope of potential interference with the source. Since the supplier is only invoked after the terminal operation commences, any modifications to the source up to the start of the terminal operation are reflected in the stream result. See Non-Interference for more details.

Parameters:

supplier - a Supplier of a Spliterator.OfLong

characteristics - Spliterator characteristics of the supplied Spliterator.OfLong. The characteristics must be equal to supplier.get().characteristics(), otherwise undefined behavior may occur when terminal operation commences.

parallel - if true then the returned stream is a parallel stream; if false the returned stream is a sequential stream.

Returns:

a new sequential or parallel LongStream

See Also:

longStream(java8.util.Spliterator.OfLong, boolean)

doubleStream

public static DoubleStream doubleStream(Spliterator.OfDouble spliterator,
                                        boolean parallel)

Creates a new sequential or parallel DoubleStream from a Spliterator.OfDouble.

The spliterator is only traversed, split, or queried for estimated size after the terminal operation of the stream pipeline commences.

It is strongly recommended the spliterator report a characteristic of IMMUTABLE or CONCURRENT, or be late-binding. Otherwise, doubleStream(java8.util.function.Supplier, int, boolean) should be used to reduce the scope of potential interference with the source. See Non-Interference for more details.

Parameters:

spliterator - A Spliterator.OfDouble describing the stream elements

parallel - if true then the returned stream is a parallel stream; if false the returned stream is a sequential stream.

Returns:

a new sequential or parallel DoubleStream

doubleStream

public static DoubleStream doubleStream(Supplier<? extends Spliterator.OfDouble> supplier,
                                        int characteristics,
                                        boolean parallel)

Creates a new sequential or parallel DoubleStream from a Supplier of Spliterator.OfDouble.

The Supplier.get() method will be invoked on the supplier no more than once, and only after the terminal operation of the stream pipeline commences.

For spliterators that report a characteristic of IMMUTABLE or CONCURRENT, or that are late-binding, it is likely more efficient to use doubleStream(java8.util.Spliterator.OfDouble, boolean) instead.

The use of a Supplier in this form provides a level of indirection that reduces the scope of potential interference with the source. Since the supplier is only invoked after the terminal operation commences, any modifications to the source up to the start of the terminal operation are reflected in the stream result. See Non-Interference for more details.

Parameters:

supplier - A Supplier of a Spliterator.OfDouble

characteristics - Spliterator characteristics of the supplied Spliterator.OfDouble. The characteristics must be equal to supplier.get().characteristics(), otherwise undefined behavior may occur when terminal operation commences.

parallel - if true then the returned stream is a parallel stream; if false the returned stream is a sequential stream.

Returns:

a new sequential or parallel DoubleStream

See Also:

doubleStream(java8.util.Spliterator.OfDouble, boolean)