Added in API level 24

Stream

interface Stream<T : Any!> : BaseStream<T, Stream<T>!>

java.util.stream.Stream

A sequence of elements supporting sequential and parallel aggregate operations. The following example illustrates an aggregate operation using Stream and IntStream:

<code>int sum = widgets.stream()
                       .filter(w -&gt; w.getColor() == RED)
                       .mapToInt(w -&gt; w.getWeight())
                       .sum();
  </code>

In this example, widgets is a Collection<Widget>. We create a stream of Widget objects via Collection.stream(), filter it to produce a stream containing only the red widgets, and then transform it into a stream of int values representing the weight of each red widget. Then this stream is summed to produce a total weight.

In addition to Stream, which is a stream of object references, there are primitive specializations for IntStream, LongStream, and DoubleStream, all of which are referred to as "streams" and conform to the characteristics and restrictions described here.

To perform a computation, stream operations are composed into a stream pipeline. A stream pipeline consists of a source (which might be an array, a collection, a generator function, an I/O channel, etc), zero or more intermediate operations (which transform a stream into another stream, such as Stream#filter(Predicate)), and a terminal operation (which produces a result or side-effect, such as Stream#count() or Stream#forEach(Consumer)). Streams are lazy; computation on the source data is only performed when the terminal operation is initiated, and source elements are consumed only as needed.

A stream implementation is permitted significant latitude in optimizing the computation of the result. For example, a stream implementation is free to elide operations (or entire stages) from a stream pipeline -- and therefore elide invocation of behavioral parameters -- if it can prove that it would not affect the result of the computation. This means that side-effects of behavioral parameters may not always be executed and should not be relied upon, unless otherwise specified (such as by the terminal operations forEach and forEachOrdered). (For a specific example of such an optimization, see the API note documented on the count operation. For more detail, see the side-effects section of the stream package documentation.)

Collections and streams, while bearing some superficial similarities, have different goals. Collections are primarily concerned with the efficient management of, and access to, their elements. By contrast, streams do not provide a means to directly access or manipulate their elements, and are instead concerned with declaratively describing their source and the computational operations which will be performed in aggregate on that source. However, if the provided stream operations do not offer the desired functionality, the iterator() and spliterator() operations can be used to perform a controlled traversal.

A stream pipeline, like the "widgets" example above, can be viewed as a query on the stream source. Unless the source was explicitly designed for concurrent modification (such as a ConcurrentHashMap), unpredictable or erroneous behavior may result from modifying the stream source while it is being queried.

Most stream operations accept parameters that describe user-specified behavior, such as the lambda expression w -> w.getWeight() passed to mapToInt in the example above. To preserve correct behavior, these behavioral parameters:

must be non-interfering (they do not modify the stream source); and
in most cases must be stateless (their result should not depend on any state that might change during execution of the stream pipeline).

Such parameters are always instances of a functional interface such as java.util.function.Function, and are often lambda expressions or method references. Unless otherwise specified these parameters must be non-null.

A stream should be operated on (invoking an intermediate or terminal stream operation) only once. This rules out, for example, "forked" streams, where the same source feeds two or more pipelines, or multiple traversals of the same stream. A stream implementation may throw IllegalStateException if it detects that the stream is being reused. However, since some stream operations may return their receiver rather than a new stream object, it may not be possible to detect reuse in all cases.

Streams have a close() method and implement AutoCloseable. Operating on a stream after it has been closed will throw IllegalStateException. Most stream instances do not actually need to be closed after use, as they are backed by collections, arrays, or generating functions, which require no special resource management. Generally, only streams whose source is an IO channel, such as those returned by Files#lines(Path), will require closing. If a stream does require closing, it must be opened as a resource within a try-with-resources statement or similar control structure to ensure that it is closed promptly after its operations have completed.

Stream pipelines may execute either sequentially or in parallel. This execution mode is a property of the stream. Streams are created with an initial choice of sequential or parallel execution. (For example, Collection.stream() creates a sequential stream, and Collection.parallelStream() creates a parallel one.) This choice of execution mode may be modified by the sequential() or parallel() methods, and may be queried with the isParallel() method.

Summary

Nested classes
abstract	`Builder` A mutable builder for a `Stream`.

Public methods
abstract Boolean	`allMatch(predicate: Predicate<in T>!)` Returns whether all elements of this stream match the provided predicate.
abstract Boolean	`anyMatch(predicate: Predicate<in T>!)` Returns whether any elements of this stream match the provided predicate.
open static Stream.Builder<T>!	`builder()` Returns a builder for a `Stream`.
abstract R	`collect(supplier: Supplier<R>!, accumulator: BiConsumer<R, in T>!, combiner: BiConsumer<R, R>!)` Performs a mutable reduction operation on the elements of this stream.
abstract R	`collect(collector: Collector<in T, A, R>!)` Performs a mutable reduction operation on the elements of this stream using a `Collector`.
open static Stream<T>!	`concat(a: Stream<out T>!, b: Stream<out T>!)` Creates a lazily concatenated stream whose elements are all the elements of the first stream followed by all the elements of the second stream.
abstract Long	`count()` Returns the count of elements in this stream.
abstract Stream<T>!	`distinct()` Returns a stream consisting of the distinct elements (according to `Object#equals(Object)`) of this stream.
open Stream<T>!	`dropWhile(predicate: Predicate<in T>!)` Returns, if this stream is ordered, a stream consisting of the remaining elements of this stream after dropping the longest prefix of elements that match the given predicate.
open static Stream<T>!	`empty()` Returns an empty sequential `Stream`.
abstract Stream<T>!	`filter(predicate: Predicate<in T>!)` Returns a stream consisting of the elements of this stream that match the given predicate.
abstract Optional<T>!	`findAny()` Returns an `Optional` describing some element of the stream, or an empty `Optional` if the stream is empty.
abstract Optional<T>!	`findFirst()` Returns an `Optional` describing the first element of this stream, or an empty `Optional` if the stream is empty.
abstract Stream<R>!	`flatMap(mapper: Function<in T, out Stream<out R>!>!)` Returns a stream consisting of the results of replacing each element of this stream with the contents of a mapped stream produced by applying the provided mapping function to each element.
abstract DoubleStream!	`flatMapToDouble(mapper: Function<in T, out DoubleStream!>!)` Returns an `DoubleStream` consisting of the results of replacing each element of this stream with the contents of a mapped stream produced by applying the provided mapping function to each element.
abstract IntStream!	`flatMapToInt(mapper: Function<in T, out IntStream!>!)` Returns an `IntStream` consisting of the results of replacing each element of this stream with the contents of a mapped stream produced by applying the provided mapping function to each element.
abstract LongStream!	`flatMapToLong(mapper: Function<in T, out LongStream!>!)` Returns an `LongStream` consisting of the results of replacing each element of this stream with the contents of a mapped stream produced by applying the provided mapping function to each element.
abstract Unit	`forEach(action: Consumer<in T>!)` Performs an action for each element of this stream.
abstract Unit	`forEachOrdered(action: Consumer<in T>!)` Performs an action for each element of this stream, in the encounter order of the stream if the stream has a defined encounter order.
open static Stream<T>!	`generate(s: Supplier<out T>!)` Returns an infinite sequential unordered stream where each element is generated by the provided `Supplier`.
open static Stream<T>!	`iterate(seed: T, f: UnaryOperator<T>!)` 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.
open static Stream<T>!	`iterate(seed: T, hasNext: Predicate<in T>!, next: UnaryOperator<T>!)` Returns a sequential ordered `Stream` produced by iterative application of the given `next` function to an initial element, conditioned on satisfying the given `hasNext` predicate.
abstract Stream<T>!	`limit(maxSize: Long)` Returns a stream consisting of the elements of this stream, truncated to be no longer than `maxSize` in length.
abstract Stream<R>!	`map(mapper: Function<in T, out R>!)` Returns a stream consisting of the results of applying the given function to the elements of this stream.
open Stream<R>!	`mapMulti(mapper: BiConsumer<in T, in Consumer<R>!>!)` Returns a stream consisting of the results of replacing each element of this stream with multiple elements, specifically zero or more elements.
open DoubleStream!	`mapMultiToDouble(mapper: BiConsumer<in T, in DoubleConsumer!>!)` Returns a `DoubleStream` consisting of the results of replacing each element of this stream with multiple elements, specifically zero or more elements.
open IntStream!	`mapMultiToInt(mapper: BiConsumer<in T, in IntConsumer!>!)` Returns an `IntStream` consisting of the results of replacing each element of this stream with multiple elements, specifically zero or more elements.
open LongStream!	`mapMultiToLong(mapper: BiConsumer<in T, in LongConsumer!>!)` Returns a `LongStream` consisting of the results of replacing each element of this stream with multiple elements, specifically zero or more elements.
abstract DoubleStream!	`mapToDouble(mapper: ToDoubleFunction<in T>!)` Returns a `DoubleStream` consisting of the results of applying the given function to the elements of this stream.
abstract IntStream!	`mapToInt(mapper: ToIntFunction<in T>!)` Returns an `IntStream` consisting of the results of applying the given function to the elements of this stream.
abstract LongStream!	`mapToLong(mapper: ToLongFunction<in T>!)` Returns a `LongStream` consisting of the results of applying the given function to the elements of this stream.
abstract Optional<T>!	`max(comparator: Comparator<in T>!)` Returns the maximum element of this stream according to the provided `Comparator`.
abstract Optional<T>!	`min(comparator: Comparator<in T>!)` Returns the minimum element of this stream according to the provided `Comparator`.
abstract Boolean	`noneMatch(predicate: Predicate<in T>!)` Returns whether no elements of this stream match the provided predicate.
open static Stream<T>!	`of(t: T)` Returns a sequential `Stream` containing a single element.
open static Stream<T>!	`of(vararg values: T)` Returns a sequential ordered stream whose elements are the specified values.
open static Stream<T>!	`ofNullable(t: T)` Returns a sequential `Stream` containing a single element, if non-null, otherwise returns an empty `Stream`.
abstract Stream<T>!	`peek(action: Consumer<in T>!)` Returns a stream consisting of the elements of this stream, additionally performing the provided action on each element as elements are consumed from the resulting stream.
abstract T	`reduce(identity: T, accumulator: BinaryOperator<T>!)` Performs a reduction on the elements of this stream, using the provided identity value and an associative accumulation function, and returns the reduced value.
abstract Optional<T>!	`reduce(accumulator: BinaryOperator<T>!)` Performs a reduction on the elements of this stream, using an associative accumulation function, and returns an `Optional` describing the reduced value, if any.
abstract U	`reduce(identity: U, accumulator: BiFunction<U, in T, U>!, combiner: BinaryOperator<U>!)` Performs a reduction on the elements of this stream, using the provided identity, accumulation and combining functions.
abstract Stream<T>!	`skip(n: Long)` Returns a stream consisting of the remaining elements of this stream after discarding the first `n` elements of the stream.
abstract Stream<T>!	`sorted()` Returns a stream consisting of the elements of this stream, sorted according to natural order.
abstract Stream<T>!	`sorted(comparator: Comparator<in T>!)` Returns a stream consisting of the elements of this stream, sorted according to the provided `Comparator`.
open Stream<T>!	`takeWhile(predicate: Predicate<in T>!)` Returns, if this stream is ordered, a stream consisting of the longest prefix of elements taken from this stream that match the given predicate.
abstract Array<Any!>!	`toArray()` Returns an array containing the elements of this stream.
abstract Array<A>!	`toArray(generator: IntFunction<Array<A>!>!)` Returns an array containing the elements of this stream, using the provided `generator` function to allocate the returned array, as well as any additional arrays that might be required for a partitioned execution or for resizing.
open MutableList<T>!	`toList()` Accumulates the elements of this stream into a `List`.

Inherited functions

From class BaseStream

`Unit`	`close()` Closes this stream, causing all close handlers for this stream pipeline to be called.
`Boolean`	`isParallel()` Returns whether this stream, if a terminal operation were to be executed, would execute in parallel. Calling this method after invoking an terminal stream operation method may yield unpredictable results.
`MutableIterator<T>!`	`iterator()` Returns an iterator for the elements of this stream. This is a terminal operation.
`S`	`onClose(closeHandler: Runnable!)` Returns an equivalent stream with an additional close handler. Close handlers are run when the `close()` method is called on the stream, and are executed in the order they were added. All close handlers are run, even if earlier close handlers throw exceptions. If any close handler throws an exception, the first exception thrown will be relayed to the caller of `close()`, with any remaining exceptions added to that exception as suppressed exceptions (unless one of the remaining exceptions is the same exception as the first exception, since an exception cannot suppress itself.) May return itself. This is an intermediate operation.
`S`	`parallel()` Returns an equivalent stream that is parallel. May return itself, either because the stream was already parallel, or because the underlying stream state was modified to be parallel. This is an intermediate operation.
`S`	`sequential()` Returns an equivalent stream that is sequential. May return itself, either because the stream was already sequential, or because the underlying stream state was modified to be sequential. This is an intermediate operation.
`Spliterator<T>!`	`spliterator()` Returns a spliterator for the elements of this stream. This is a terminal operation. The returned spliterator should report the set of characteristics derived from the stream pipeline (namely the characteristics derived from the stream source spliterator and the intermediate operations). Implementations may report a sub-set of those characteristics. For example, it may be too expensive to compute the entire set for some or all possible stream pipelines.
`S`	`unordered()` Returns an equivalent stream that is unordered. May return itself, either because the stream was already unordered, or because the underlying stream state was modified to be unordered. This is an intermediate operation.

Public methods

allMatch

Added in API level 24

abstract fun allMatch(predicate: Predicate<in T>!): Boolean

Returns whether all elements of this stream match the provided predicate. May not evaluate the predicate on all elements if not necessary for determining the result. If the stream is empty then true is returned and the predicate is not evaluated.

This is a short-circuiting terminal operation.

Parameters
`predicate`	Predicate<in T>!: a non-interfering, stateless predicate to apply to elements of this stream

Return
`Boolean`	`true` if either all elements of the stream match the provided predicate or the stream is empty, otherwise `false`

anyMatch

Added in API level 24

abstract fun anyMatch(predicate: Predicate<in T>!): Boolean

Returns whether any elements of this stream match the provided predicate. May not evaluate the predicate on all elements if not necessary for determining the result. If the stream is empty then false is returned and the predicate is not evaluated.

This is a short-circuiting terminal operation.

Parameters
`predicate`	Predicate<in T>!: a non-interfering, stateless predicate to apply to elements of this stream

Return
`Boolean`	`true` if any elements of the stream match the provided predicate, otherwise `false`

builder

Added in API level 24

open static fun <T : Any!> builder(): Stream.Builder<T>!

Returns a builder for a Stream.

Parameters
`<T>`	type of elements

Return
`Stream.Builder<T>!`	a stream builder

collect

Added in API level 24

abstract fun <R : Any!> collect(
    supplier: Supplier<R>!, 
    accumulator: BiConsumer<R, in T>!, 
    combiner: BiConsumer<R, R>!
): R

Performs a mutable reduction operation on the elements of this stream. A mutable reduction is one in which the reduced value is a mutable result container, such as an ArrayList, and elements are incorporated by updating the state of the result rather than by replacing the result. This produces a result equivalent to:

<code>R result = supplier.get();
      for (T element : this stream)
          accumulator.accept(result, element);
      return result;
  </code>

Like reduce(java.lang.Object,java.util.function.BinaryOperator), collect operations can be parallelized without requiring additional synchronization.

This is a terminal operation.

Parameters
`<R>`	the type of the mutable result container
`supplier`	Supplier<R>!: a function that creates a new mutable result container. For a parallel execution, this function may be called multiple times and must return a fresh value each time.
`accumulator`	BiConsumer<R, in T>!: an associative, non-interfering, stateless function that must fold an element into a result container.
`combiner`	BiConsumer<R, R>!: an associative, non-interfering, stateless function that accepts two partial result containers and merges them, which must be compatible with the accumulator function. The combiner function must fold the elements from the second result container into the first result container.

Return
`R`	the result of the reduction

collect

Added in API level 24

abstract fun <R : Any!, A : Any!> collect(collector: Collector<in T, A, R>!): R

Performs a mutable reduction operation on the elements of this stream using a Collector. A Collector encapsulates the functions used as arguments to collect(java.util.function.Supplier,java.util.function.BiConsumer,java.util.function.BiConsumer), allowing for reuse of collection strategies and composition of collect operations such as multiple-level grouping or partitioning.

If the stream is parallel, and the Collector is concurrent, and either the stream is unordered or the collector is unordered, then a concurrent reduction will be performed (see Collector for details on concurrent reduction.)

This is a terminal operation.

When executed in parallel, multiple intermediate results may be instantiated, populated, and merged so as to maintain isolation of mutable data structures. Therefore, even when executed in parallel with non-thread-safe data structures (such as ArrayList), no additional synchronization is needed for a parallel reduction.

Parameters
`<R>`	the type of the result
`<A>`	the intermediate accumulation type of the `Collector`
`collector`	Collector<in T, A, R>!: the `Collector` describing the reduction

Return
`R`	the result of the reduction

See Also

#collect(Supplier, BiConsumer, BiConsumer)
java.util.stream.Collectors

concat

Added in API level 24

open static fun <T : Any!> concat(
    a: Stream<out T>!, 
    b: Stream<out T>!
): Stream<T>!

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.

This method operates on the two input streams and binds each stream to its source. As a result subsequent modifications to an input stream source may not be reflected in the concatenated stream result.

Parameters
`<T>`	The type of stream elements
`a`	Stream<out T>!: the first stream
`b`	Stream<out T>!: the second stream

Return
`Stream<T>!`	the concatenation of the two input streams

count

Added in API level 24

abstract fun count(): Long

Returns the count of elements in this stream. This is a special case of a reduction and is equivalent to:

<code>return mapToLong(e -&gt; 1L).sum();
  </code>

This is a terminal operation.

Return
`Long`	the count of elements in this stream

distinct

Added in API level 24

abstract fun distinct(): Stream<T>!

Returns a stream consisting of the distinct elements (according to Object#equals(Object)) of this stream.

For ordered streams, the selection of distinct elements is stable (for duplicated elements, the element appearing first in the encounter order is preserved.) For unordered streams, no stability guarantees are made.

This is a stateful intermediate operation.

Return
`Stream<T>!`	the new stream

dropWhile

Added in API level 34

open fun dropWhile(predicate: Predicate<in T>!): Stream<T>!

Returns, if this stream is ordered, a stream consisting of the remaining elements of this stream after dropping the longest prefix of elements that match the given predicate. Otherwise returns, if this stream is unordered, a stream consisting of the remaining elements of this stream after dropping a subset of elements that match the given predicate.

If this stream is ordered then the longest prefix is a contiguous sequence of elements of this stream that match the given predicate. The first element of the sequence is the first element of this stream, and the element immediately following the last element of the sequence does not match the given predicate.

If this stream is unordered, and some (but not all) elements of this stream match the given predicate, then the behavior of this operation is nondeterministic; it is free to drop any subset of matching elements (which includes the empty set).

Independent of whether this stream is ordered or unordered if all elements of this stream match the given predicate then this operation drops all elements (the result is an empty stream), or if no elements of the stream match the given predicate then no elements are dropped (the result is the same as the input).

This is a stateful intermediate operation.

Parameters
`predicate`	Predicate<in T>!: a non-interfering, stateless predicate to apply to elements to determine the longest prefix of elements.

Return
`Stream<T>!`	the new stream

empty

Added in API level 24

open static fun <T : Any!> empty(): Stream<T>!

Returns an empty sequential Stream.

Parameters
`<T>`	the type of stream elements

Return
`Stream<T>!`	an empty sequential stream

filter

Added in API level 24

abstract fun filter(predicate: Predicate<in T>!): Stream<T>!

Returns a stream consisting of the elements of this stream that match the given predicate.

This is an intermediate operation.

Parameters
`predicate`	Predicate<in T>!: a non-interfering, stateless predicate to apply to each element to determine if it should be included

Return
`Stream<T>!`	the new stream

findAny

Added in API level 24

abstract fun findAny(): Optional<T>!

Returns an Optional describing some element of the stream, or an empty Optional if the stream is empty.

This is a short-circuiting terminal operation.

The behavior of this operation is explicitly nondeterministic; it is free to select any element in the stream. This is to allow for maximal performance in parallel operations; the cost is that multiple invocations on the same source may not return the same result. (If a stable result is desired, use findFirst() instead.)

Return
`Optional<T>!`	an `Optional` describing some element of this stream, or an empty `Optional` if the stream is empty

Exceptions
`java.lang.NullPointerException`	if the element selected is null

See Also

#findFirst()

findFirst

Added in API level 24

abstract fun findFirst(): Optional<T>!

Returns an Optional describing the first element of this stream, or an empty Optional if the stream is empty. If the stream has no encounter order, then any element may be returned.

This is a short-circuiting terminal operation.

Return
`Optional<T>!`	an `Optional` describing the first element of this stream, or an empty `Optional` if the stream is empty

Exceptions
`java.lang.NullPointerException`	if the element selected is null

flatMap

Added in API level 24

abstract fun <R : Any!> flatMap(mapper: Function<in T, out Stream<out R>!>!): Stream<R>!

Returns a stream consisting of the results of replacing each element of this stream with the contents of a mapped stream produced by applying the provided mapping function to each element. Each mapped stream is closed after its contents have been placed into this stream. (If a mapped stream is null an empty stream is used, instead.)

This is an intermediate operation.

Parameters
`<R>`	The element type of the new stream
`mapper`	Function<in T, out Stream<out R>!>!: a non-interfering, stateless function to apply to each element which produces a stream of new values

Return
`Stream<R>!`	the new stream

See Also

#mapMulti

flatMapToDouble

Added in API level 24

abstract fun flatMapToDouble(mapper: Function<in T, out DoubleStream!>!): DoubleStream!

Returns an DoubleStream consisting of the results of replacing each element of this stream with the contents of a mapped stream produced by applying the provided mapping function to each element. Each mapped stream is closed after its contents have placed been into this stream. (If a mapped stream is null an empty stream is used, instead.)

This is an intermediate operation.

Parameters
`mapper`	Function<in T, out DoubleStream!>!: a non-interfering, stateless function to apply to each element which produces a stream of new values

Return
`DoubleStream!`	the new stream

See Also

#flatMap(Function)

flatMapToInt

Added in API level 24

abstract fun flatMapToInt(mapper: Function<in T, out IntStream!>!): IntStream!

Returns an IntStream consisting of the results of replacing each element of this stream with the contents of a mapped stream produced by applying the provided mapping function to each element. Each mapped stream is closed after its contents have been placed into this stream. (If a mapped stream is null an empty stream is used, instead.)

This is an intermediate operation.

Parameters
`mapper`	Function<in T, out IntStream!>!: a non-interfering, stateless function to apply to each element which produces a stream of new values

Return
`IntStream!`	the new stream

See Also

#flatMap(Function)

flatMapToLong

Added in API level 24

abstract fun flatMapToLong(mapper: Function<in T, out LongStream!>!): LongStream!

Returns an LongStream consisting of the results of replacing each element of this stream with the contents of a mapped stream produced by applying the provided mapping function to each element. Each mapped stream is closed after its contents have been placed into this stream. (If a mapped stream is null an empty stream is used, instead.)

This is an intermediate operation.

Parameters
`mapper`	Function<in T, out LongStream!>!: a non-interfering, stateless function to apply to each element which produces a stream of new values

Return
`LongStream!`	the new stream

See Also

#flatMap(Function)

forEach

Added in API level 24

abstract fun forEach(action: Consumer<in T>!): Unit

Performs an action for each element of this stream.

This is a terminal operation.

The behavior of this operation is explicitly nondeterministic. For parallel stream pipelines, this operation does not guarantee to respect the encounter order of the stream, as doing so would sacrifice the benefit of parallelism. For any given element, the action may be performed at whatever time and in whatever thread the library chooses. If the action accesses shared state, it is responsible for providing the required synchronization.

Parameters
`action`	Consumer<in T>!: a non-interfering action to perform on the elements

forEachOrdered

Added in API level 24

abstract fun forEachOrdered(action: Consumer<in T>!): Unit

Performs an action for each element of this stream, in the encounter order of the stream if the stream has a defined encounter order.

This is a terminal operation.

This operation processes the elements one at a time, in encounter order if one exists. Performing the action for one element happens-before performing the action for subsequent elements, but for any given element, the action may be performed in whatever thread the library chooses.

Parameters
`action`	Consumer<in T>!: a non-interfering action to perform on the elements

See Also

#forEach(Consumer)

generate

Added in API level 24

open static fun <T : Any!> generate(s: Supplier<out T>!): Stream<T>!

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.

Parameters
`<T>`	the type of stream elements
`s`	Supplier<out T>!: the `Supplier` of generated elements

Return
`Stream<T>!`	a new infinite sequential unordered `Stream`

iterate

Added in API level 24

open static fun <T : Any!> iterate(
    seed: T, 
    f: UnaryOperator<T>!
): Stream<T>!

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.

The action of applying f for one element happens-before the action of applying f for subsequent elements. For any given element the action may be performed in whatever thread the library chooses.

Parameters
`<T>`	the type of stream elements
`seed`	T: the initial element
`f`	UnaryOperator<T>!: a function to be applied to the previous element to produce a new element

Return
`Stream<T>!`	a new sequential `Stream`

iterate

Added in API level 34

open static fun <T : Any!> iterate(
    seed: T, 
    hasNext: Predicate<in T>!, 
    next: UnaryOperator<T>!
): Stream<T>!

Returns a sequential ordered Stream produced by iterative application of the given next function to an initial element, conditioned on satisfying the given hasNext predicate. The stream terminates as soon as the hasNext predicate returns false.

Stream.iterate should produce the same sequence of elements as produced by the corresponding for-loop:

<code>for (T index=seed; hasNext.test(index); index = next.apply(index)) {
          ...
      }
  </code>

The resulting sequence may be empty if the hasNext predicate does not hold on the seed value. Otherwise the first element will be the supplied seed value, the next element (if present) will be the result of applying the next function to the seed value, and so on iteratively until the hasNext predicate indicates that the stream should terminate.

The action of applying the hasNext predicate to an element happens-before the action of applying the next function to that element. The action of applying the next function for one element happens-before the action of applying the hasNext predicate for subsequent elements. For any given element an action may be performed in whatever thread the library chooses.

Parameters
`<T>`	the type of stream elements
`seed`	T: the initial element
`hasNext`	Predicate<in T>!: a predicate to apply to elements to determine when the stream must terminate.
`next`	UnaryOperator<T>!: a function to be applied to the previous element to produce a new element

Return
`Stream<T>!`	a new sequential `Stream`

limit

Added in API level 24

abstract fun limit(maxSize: Long): Stream<T>!

Returns a stream consisting of the elements of this stream, truncated to be no longer than maxSize in length.

This is a short-circuiting stateful intermediate operation.

Parameters
`maxSize`	Long: the number of elements the stream should be limited to

Return
`Stream<T>!`	the new stream

Exceptions
`java.lang.IllegalArgumentException`	if `maxSize` is negative

map

Added in API level 24

abstract fun <R : Any!> map(mapper: Function<in T, out R>!): Stream<R>!

Returns a stream consisting of the results of applying the given function to the elements of this stream.

This is an intermediate operation.

Parameters
`<R>`	The element type of the new stream
`mapper`	Function<in T, out R>!: a non-interfering, stateless function to apply to each element

Return
`Stream<R>!`	the new stream

mapMulti

Added in API level 34

open fun <R : Any!> mapMulti(mapper: BiConsumer<in T, in Consumer<R>!>!): Stream<R>!

Returns a stream consisting of the results of replacing each element of this stream with multiple elements, specifically zero or more elements. Replacement is performed by applying the provided mapping function to each element in conjunction with a consumer argument that accepts replacement elements. The mapping function calls the consumer zero or more times to provide the replacement elements.

This is an intermediate operation.

If the consumer argument is used outside the scope of its application to the mapping function, the results are undefined.

Parameters
`<R>`	The element type of the new stream
`mapper`	BiConsumer<in T, in Consumer<R>!>!: a non-interfering, stateless function that generates replacement elements

Return
`Stream<R>!`	the new stream

See Also

#flatMap

mapMultiToDouble

Added in API level 34

open fun mapMultiToDouble(mapper: BiConsumer<in T, in DoubleConsumer!>!): DoubleStream!

Returns a DoubleStream consisting of the results of replacing each element of this stream with multiple elements, specifically zero or more elements. Replacement is performed by applying the provided mapping function to each element in conjunction with a consumer argument that accepts replacement elements. The mapping function calls the consumer zero or more times to provide the replacement elements.

This is an intermediate operation.

If the consumer argument is used outside the scope of its application to the mapping function, the results are undefined.

Parameters
`mapper`	BiConsumer<in T, in DoubleConsumer!>!: a non-interfering, stateless function that generates replacement elements

Return
`DoubleStream!`	the new stream

See Also

#mapMulti

mapMultiToInt

Added in API level 34

open fun mapMultiToInt(mapper: BiConsumer<in T, in IntConsumer!>!): IntStream!

Returns an IntStream consisting of the results of replacing each element of this stream with multiple elements, specifically zero or more elements. Replacement is performed by applying the provided mapping function to each element in conjunction with a consumer argument that accepts replacement elements. The mapping function calls the consumer zero or more times to provide the replacement elements.

This is an intermediate operation.

If the consumer argument is used outside the scope of its application to the mapping function, the results are undefined.

Parameters
`mapper`	BiConsumer<in T, in IntConsumer!>!: a non-interfering, stateless function that generates replacement elements

Return
`IntStream!`	the new stream

See Also

#mapMulti

mapMultiToLong

Added in API level 34

open fun mapMultiToLong(mapper: BiConsumer<in T, in LongConsumer!>!): LongStream!

Returns a LongStream consisting of the results of replacing each element of this stream with multiple elements, specifically zero or more elements. Replacement is performed by applying the provided mapping function to each element in conjunction with a consumer argument that accepts replacement elements. The mapping function calls the consumer zero or more times to provide the replacement elements.

This is an intermediate operation.

If the consumer argument is used outside the scope of its application to the mapping function, the results are undefined.

Parameters
`mapper`	BiConsumer<in T, in LongConsumer!>!: a non-interfering, stateless function that generates replacement elements

Return
`LongStream!`	the new stream

See Also

#mapMulti

mapToDouble

Added in API level 24

abstract fun mapToDouble(mapper: ToDoubleFunction<in T>!): DoubleStream!

Returns a DoubleStream consisting of the results of applying the given function to the elements of this stream.

This is an intermediate operation.

Parameters
`mapper`	ToDoubleFunction<in T>!: a non-interfering, stateless function to apply to each element

Return
`DoubleStream!`	the new stream

mapToInt

Added in API level 24

abstract fun mapToInt(mapper: ToIntFunction<in T>!): IntStream!

Returns an IntStream consisting of the results of applying the given function to the elements of this stream.

This is an intermediate operation.

Parameters
`mapper`	ToIntFunction<in T>!: a non-interfering, stateless function to apply to each element

Return
`IntStream!`	the new stream

mapToLong

Added in API level 24

abstract fun mapToLong(mapper: ToLongFunction<in T>!): LongStream!

Returns a LongStream consisting of the results of applying the given function to the elements of this stream.

This is an intermediate operation.

Parameters
`mapper`	ToLongFunction<in T>!: a non-interfering, stateless function to apply to each element

Return
`LongStream!`	the new stream

max

Added in API level 24

abstract fun max(comparator: Comparator<in T>!): Optional<T>!

Returns the maximum element of this stream according to the provided Comparator. This is a special case of a reduction.

This is a terminal operation.

Parameters
`comparator`	Comparator<in T>!: a non-interfering, stateless `Comparator` to compare elements of this stream

Return
`Optional<T>!`	an `Optional` describing the maximum element of this stream, or an empty `Optional` if the stream is empty

Exceptions
`java.lang.NullPointerException`	if the maximum element is null

min

Added in API level 24

abstract fun min(comparator: Comparator<in T>!): Optional<T>!

Returns the minimum element of this stream according to the provided Comparator. This is a special case of a reduction.

This is a terminal operation.

Parameters
`comparator`	Comparator<in T>!: a non-interfering, stateless `Comparator` to compare elements of this stream

Return
`Optional<T>!`	an `Optional` describing the minimum element of this stream, or an empty `Optional` if the stream is empty

Exceptions
`java.lang.NullPointerException`	if the minimum element is null

noneMatch

Added in API level 24

abstract fun noneMatch(predicate: Predicate<in T>!): Boolean

Returns whether no elements of this stream match the provided predicate. May not evaluate the predicate on all elements if not necessary for determining the result. If the stream is empty then true is returned and the predicate is not evaluated.

This is a short-circuiting terminal operation.

Parameters
`predicate`	Predicate<in T>!: a non-interfering, stateless predicate to apply to elements of this stream

Return
`Boolean`	`true` if either no elements of the stream match the provided predicate or the stream is empty, otherwise `false`

of

Added in API level 24

open static fun <T : Any!> of(t: T): Stream<T>!

Returns a sequential Stream containing a single element.

Parameters
`t`	T: the single element
`<T>`	the type of stream elements

Return
`Stream<T>!`	a singleton sequential stream

of

Added in API level 24

@SafeVarargs open static fun <T : Any!> of(vararg values: T): Stream<T>!

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

Parameters
`<T>`	the type of stream elements
`values`	T: the elements of the new stream

Return
`Stream<T>!`	the new stream

ofNullable

Added in API level 34

open static fun <T : Any!> ofNullable(t: T): Stream<T>!

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

Parameters
`t`	T: the single element
`<T>`	the type of stream elements

Return
`Stream<T>!`	a stream with a single element if the specified element is non-null, otherwise an empty stream

peek

Added in API level 24

abstract fun peek(action: Consumer<in T>!): Stream<T>!

Returns a stream consisting of the elements of this stream, additionally performing the provided action on each element as elements are consumed from the resulting stream.

This is an intermediate operation.

For parallel stream pipelines, the action may be called at whatever time and in whatever thread the element is made available by the upstream operation. If the action modifies shared state, it is responsible for providing the required synchronization.

Parameters
`action`	Consumer<in T>!: a non-interfering action to perform on the elements as they are consumed from the stream

Return
`Stream<T>!`	the new stream

reduce

Added in API level 24

abstract fun reduce(
    identity: T, 
    accumulator: BinaryOperator<T>!
): T

Performs a reduction on the elements of this stream, using the provided identity value and an associative accumulation function, and returns the reduced value. This is equivalent to:

<code>T result = identity;
      for (T element : this stream)
          result = accumulator.apply(result, element)
      return result;
  </code>

but is not constrained to execute sequentially.

The identity value must be an identity for the accumulator function. This means that for all t, accumulator.apply(identity, t) is equal to t. The accumulator function must be an associative function.

This is a terminal operation.

Parameters
`identity`	T: the identity value for the accumulating function
`accumulator`	BinaryOperator<T>!: an associative, non-interfering, stateless function for combining two values

Return
`T`	the result of the reduction

reduce

Added in API level 24

abstract fun reduce(accumulator: BinaryOperator<T>!): Optional<T>!

Performs a reduction on the elements of this stream, using an associative accumulation function, and returns an Optional describing the reduced value, if any. This is equivalent to:

<code>boolean foundAny = false;
      T result = null;
      for (T element : this stream) {
          if (!foundAny) {
              foundAny = true;
              result = element;
          }
          else
              result = accumulator.apply(result, element);
      }
      return foundAny ? Optional.of(result) : Optional.empty();
  </code>

but is not constrained to execute sequentially.

The accumulator function must be an associative function.

This is a terminal operation.

Parameters
`accumulator`	BinaryOperator<T>!: an associative, non-interfering, stateless function for combining two values

Return
`Optional<T>!`	an `Optional` describing the result of the reduction

Exceptions
`java.lang.NullPointerException`	if the result of the reduction is null

See Also

#reduce(Object, BinaryOperator)
#min(Comparator)
#max(Comparator)

reduce

Added in API level 24

abstract fun <U : Any!> reduce(
    identity: U, 
    accumulator: BiFunction<U, in T, U>!, 
    combiner: BinaryOperator<U>!
): U

Performs a reduction on the elements of this stream, using the provided identity, accumulation and combining functions. This is equivalent to:

<code>U result = identity;
      for (T element : this stream)
          result = accumulator.apply(result, element)
      return result;
  </code>

but is not constrained to execute sequentially.

The identity value must be an identity for the combiner function. This means that for all u, combiner(identity, u) is equal to u. Additionally, the combiner function must be compatible with the accumulator function; for all u and t, the following must hold:

<code>combiner.apply(u, accumulator.apply(identity, t)) == accumulator.apply(u, t)
  </code>

This is a terminal operation.

Parameters
`<U>`	The type of the result
`identity`	U: the identity value for the combiner function
`accumulator`	BiFunction<U, in T, U>!: an associative, non-interfering, stateless function for incorporating an additional element into a result
`combiner`	BinaryOperator<U>!: an associative, non-interfering, stateless function for combining two values, which must be compatible with the accumulator function

Return
`U`	the result of the reduction

See Also

#reduce(BinaryOperator)
#reduce(Object, BinaryOperator)

skip

Added in API level 24

abstract fun skip(n: Long): Stream<T>!

Returns a stream consisting of the remaining elements of this stream after discarding the first n elements of the stream. If this stream contains fewer than n elements then an empty stream will be returned.

This is a stateful intermediate operation.

Parameters
`n`	Long: the number of leading elements to skip

Return
`Stream<T>!`	the new stream

Exceptions
`java.lang.IllegalArgumentException`	if `n` is negative

sorted

Added in API level 24

abstract fun sorted(): Stream<T>!

Returns a stream consisting of the elements of this stream, sorted according to natural order. If the elements of this stream are not Comparable, a java.lang.ClassCastException may be thrown when the terminal operation is executed.

For ordered streams, the sort is stable. For unordered streams, no stability guarantees are made.

This is a stateful intermediate operation.

Return
`Stream<T>!`	the new stream

sorted

Added in API level 24

abstract fun sorted(comparator: Comparator<in T>!): Stream<T>!

Returns a stream consisting of the elements of this stream, sorted according to the provided Comparator.

For ordered streams, the sort is stable. For unordered streams, no stability guarantees are made.

This is a stateful intermediate operation.

Parameters
`comparator`	Comparator<in T>!: a non-interfering, stateless `Comparator` to be used to compare stream elements

Return
`Stream<T>!`	the new stream

takeWhile

Added in API level 34

open fun takeWhile(predicate: Predicate<in T>!): Stream<T>!

Returns, if this stream is ordered, a stream consisting of the longest prefix of elements taken from this stream that match the given predicate. Otherwise returns, if this stream is unordered, a stream consisting of a subset of elements taken from this stream that match the given predicate.

If this stream is unordered, and some (but not all) elements of this stream match the given predicate, then the behavior of this operation is nondeterministic; it is free to take any subset of matching elements (which includes the empty set).

Independent of whether this stream is ordered or unordered if all elements of this stream match the given predicate then this operation takes all elements (the result is the same as the input), or if no elements of the stream match the given predicate then no elements are taken (the result is an empty stream).

This is a short-circuiting stateful intermediate operation.

Parameters
`predicate`	Predicate<in T>!: a non-interfering, stateless predicate to apply to elements to determine the longest prefix of elements.

Return
`Stream<T>!`	the new stream

toArray

Added in API level 24

abstract fun toArray(): Array<Any!>!

Returns an array containing the elements of this stream.

This is a terminal operation.

Return
`Array<Any!>!`	an array, whose type is `Object`, containing the elements of this stream

toArray

Added in API level 24

abstract fun <A : Any!> toArray(generator: IntFunction<Array<A>!>!): Array<A>!

Returns an array containing the elements of this stream, using the provided generator function to allocate the returned array, as well as any additional arrays that might be required for a partitioned execution or for resizing.

This is a terminal operation.

Parameters
`<A>`	the component type of the resulting array
`generator`	IntFunction<Array<A>!>!: a function which produces a new array of the desired type and the provided length

Return
`Array<A>!`	an array containing the elements in this stream

Exceptions
`java.lang.ArrayStoreException`	if the runtime type of any element of this stream is not assignable to the runtime component type of the generated array

toList

Added in API level 34

open fun toList(): MutableList<T>!

Accumulates the elements of this stream into a List. The elements in the list will be in this stream's encounter order, if one exists. The returned List is unmodifiable; calls to any mutator method will always cause UnsupportedOperationException to be thrown. There are no guarantees on the implementation type or serializability of the returned List.

The returned instance may be value-based. Callers should make no assumptions about the identity of the returned instances. Identity-sensitive operations on these instances (reference equality (==), identity hash code, and synchronization) are unreliable and should be avoided.

This is a terminal operation.

Return
`MutableList<T>!`	a List containing the stream elements