java8.util.stream

Class RefStreams

java.lang.Object

java8.util.stream.RefStreams

public final class RefStreams
extends Object

A place for static default implementations of the new Java 8/9 static interface methods and default interface methods (takeWhile(), dropWhile()) in the Stream interface.

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 <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 <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 <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>	ofNullable(T t) Returns a sequential Stream containing a single element, if non-null, otherwise returns an empty Stream.

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

ofNullable

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

Returns a sequential Stream containing a single element, if non-null, otherwise returns an empty Stream.

Type Parameters:

T - the type of stream elements

Parameters:

t - the single element

Returns:

a stream with a single element if the specified element is non-null, otherwise an empty stream

Since:

1.9

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 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 StackOverflowError.

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:

IllegalStateException - if the builder has already transitioned to the built state