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LongStream

public interface LongStream
implements BaseStream<LongLongStream>

java.util.stream.LongStream


A sequence of primitive long-valued elements supporting sequential and parallel aggregate operations. This is the long primitive specialization of Stream.

The following example illustrates an aggregate operation using Stream and LongStream, computing the sum of the weights of the red widgets:

long sum = widgets.stream()
                       .filter(w -> w.getColor() == RED)
                       .mapToLong(w -> w.getWeight())
                       .sum();
 
See the class documentation for Stream and the package documentation for java.util.stream for additional specification of streams, stream operations, stream pipelines, and parallelism.

Summary

Nested classes

interface LongStream.Builder

A mutable builder for a LongStream

Public methods

abstract boolean allMatch(LongPredicate predicate)

Returns whether all elements of this stream match the provided predicate.

abstract boolean anyMatch(LongPredicate predicate)

Returns whether any elements of this stream match the provided predicate.

abstract DoubleStream asDoubleStream()

Returns a DoubleStream consisting of the elements of this stream, converted to double.

abstract OptionalDouble average()

Returns an OptionalDouble describing the arithmetic mean of elements of this stream, or an empty optional if this stream is empty.

abstract Stream<Long> boxed()

Returns a Stream consisting of the elements of this stream, each boxed to a Long.

static LongStream.Builder builder()

Returns a builder for a LongStream.

abstract <R> R collect(Supplier<R> supplier, ObjLongConsumer<R> accumulator, BiConsumer<R, R> combiner)

Performs a mutable reduction operation on the elements of this stream.

static LongStream concat(LongStream a, LongStream 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.

abstract long count()

Returns the count of elements in this stream.

abstract LongStream distinct()

Returns a stream consisting of the distinct elements of this stream.

static LongStream empty()

Returns an empty sequential LongStream.

abstract LongStream filter(LongPredicate predicate)

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

abstract OptionalLong findAny()

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

abstract OptionalLong findFirst()

Returns an OptionalLong describing the first element of this stream, or an empty OptionalLong if the stream is empty.

abstract LongStream flatMap(LongFunction<? extends LongStream> mapper)

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 void forEach(LongConsumer action)

Performs an action for each element of this stream.

abstract void forEachOrdered(LongConsumer action)

Performs an action for each element of this stream, guaranteeing that each element is processed in encounter order for streams that have a defined encounter order.

static LongStream generate(LongSupplier s)

Returns an infinite sequential unordered stream where each element is generated by the provided LongSupplier.

static LongStream iterate(long seed, LongUnaryOperator f)

Returns an infinite sequential ordered LongStream 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.

abstract PrimitiveIterator.OfLong iterator()

Returns an iterator for the elements of this stream.

abstract LongStream limit(long maxSize)

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

abstract LongStream map(LongUnaryOperator mapper)

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

abstract DoubleStream mapToDouble(LongToDoubleFunction mapper)

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

abstract IntStream mapToInt(LongToIntFunction mapper)

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

abstract <U> Stream<U> mapToObj(LongFunction<? extends U> mapper)

Returns an object-valued Stream consisting of the results of applying the given function to the elements of this stream.

abstract OptionalLong max()

Returns an OptionalLong describing the maximum element of this stream, or an empty optional if this stream is empty.

abstract OptionalLong min()

Returns an OptionalLong describing the minimum element of this stream, or an empty optional if this stream is empty.

abstract boolean noneMatch(LongPredicate predicate)

Returns whether no elements of this stream match the provided predicate.

static LongStream of(long... values)

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

static LongStream of(long t)

Returns a sequential LongStream containing a single element.

abstract LongStream parallel()

Returns an equivalent stream that is parallel.

abstract LongStream peek(LongConsumer action)

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.

static LongStream range(long startInclusive, long endExclusive)

Returns a sequential ordered LongStream from startInclusive (inclusive) to endExclusive (exclusive) by an incremental step of 1.

static LongStream rangeClosed(long startInclusive, long endInclusive)

Returns a sequential ordered LongStream from startInclusive (inclusive) to endInclusive (inclusive) by an incremental step of 1.

abstract OptionalLong reduce(LongBinaryOperator op)

Performs a reduction on the elements of this stream, using an associative accumulation function, and returns an OptionalLong describing the reduced value, if any.

abstract long reduce(long identity, LongBinaryOperator op)

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 LongStream sequential()

Returns an equivalent stream that is sequential.

abstract LongStream skip(long n)

Returns a stream consisting of the remaining elements of this stream after discarding the first n elements of the stream.

abstract LongStream sorted()

Returns a stream consisting of the elements of this stream in sorted order.

abstract Spliterator.OfLong spliterator()

Returns a spliterator for the elements of this stream.

abstract long sum()

Returns the sum of elements in this stream.

abstract LongSummaryStatistics summaryStatistics()

Returns a LongSummaryStatistics describing various summary data about the elements of this stream.

abstract long[] toArray()

Returns an array containing the elements of this stream.

Inherited methods

Public methods

allMatch

added in API level 24
public abstract boolean allMatch (LongPredicate predicate)

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.

API Note:
  • This method evaluates the universal quantification of the predicate over the elements of the stream (for all x P(x)). If the stream is empty, the quantification is said to be vacuously satisfied and is always true (regardless of P(x)).
Parameters
predicate LongPredicate: a non-interfering, stateless predicate to apply to elements of this stream

Returns
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
public abstract boolean anyMatch (LongPredicate predicate)

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.

API Note:
  • This method evaluates the existential quantification of the predicate over the elements of the stream (for some x P(x)).
Parameters
predicate LongPredicate: a non-interfering, stateless predicate to apply to elements of this stream

Returns
boolean true if any elements of the stream match the provided predicate, otherwise false

asDoubleStream

added in API level 24
public abstract DoubleStream asDoubleStream ()

Returns a DoubleStream consisting of the elements of this stream, converted to double.

This is an intermediate operation.

Returns
DoubleStream a DoubleStream consisting of the elements of this stream, converted to double

average

added in API level 24
public abstract OptionalDouble average ()

Returns an OptionalDouble describing the arithmetic mean of elements of this stream, or an empty optional if this stream is empty. This is a special case of a reduction.

This is a terminal operation.

Returns
OptionalDouble an OptionalDouble containing the average element of this stream, or an empty optional if the stream is empty

boxed

added in API level 24
public abstract Stream<Long> boxed ()

Returns a Stream consisting of the elements of this stream, each boxed to a Long.

This is an intermediate operation.

Returns
Stream<Long> a Stream consistent of the elements of this stream, each boxed to Long

builder

added in API level 24
public static LongStream.Builder builder ()

Returns a builder for a LongStream.

Returns
LongStream.Builder a stream builder

collect

added in API level 24
public abstract R collect (Supplier<R> supplier, 
                ObjLongConsumer<R> accumulator, 
                BiConsumer<R, R> combiner)

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:

R result = supplier.get();
     for (long element : this stream)
         accumulator.accept(result, element);
     return result;
 

Like reduce(long, LongBinaryOperator), collect operations can be parallelized without requiring additional synchronization.

This is a terminal operation.

Parameters
supplier Supplier: a function that creates a new result container. For a parallel execution, this function may be called multiple times and must return a fresh value each time.

accumulator ObjLongConsumer: an associative, non-interfering, stateless function for incorporating an additional element into a result

combiner BiConsumer: an associative, non-interfering, stateless function for combining two values, which must be compatible with the accumulator function

Returns
R the result of the reduction

concat

added in API level 24
public static LongStream concat (LongStream a, 
                LongStream 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.
Parameters
a LongStream: the first stream

b LongStream: the second stream

Returns
LongStream the concatenation of the two input streams

count

added in API level 24
public abstract long count ()

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

return map(e -> 1L).sum();
 

This is a terminal operation.

Returns
long the count of elements in this stream

distinct

added in API level 24
public abstract LongStream distinct ()

Returns a stream consisting of the distinct elements of this stream.

This is a stateful intermediate operation.

Returns
LongStream the new stream

empty

added in API level 24
public static LongStream empty ()

Returns an empty sequential LongStream.

Returns
LongStream an empty sequential stream

filter

added in API level 24
public abstract LongStream filter (LongPredicate predicate)

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

This is an intermediate operation.

Parameters
predicate LongPredicate: a non-interfering, stateless predicate to apply to each element to determine if it should be included

Returns
LongStream the new stream

findAny

added in API level 24
public abstract OptionalLong findAny ()

Returns an OptionalLong describing some element of the stream, or an empty OptionalLong 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.)

Returns
OptionalLong an OptionalLong describing some element of this stream, or an empty OptionalLong if the stream is empty

See also:

findFirst

added in API level 24
public abstract OptionalLong findFirst ()

Returns an OptionalLong describing the first element of this stream, or an empty OptionalLong 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.

Returns
OptionalLong an OptionalLong describing the first element of this stream, or an empty OptionalLong if the stream is empty

flatMap

added in API level 24
public abstract LongStream flatMap (LongFunction<? extends LongStream> mapper)

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
mapper LongFunction: a non-interfering, stateless function to apply to each element which produces a LongStream of new values

Returns
LongStream the new stream

forEach

added in API level 24
public abstract void forEach (LongConsumer action)

Performs an action for each element of this stream.

This is a terminal operation.

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 LongConsumer: a non-interfering action to perform on the elements

forEachOrdered

added in API level 24
public abstract void forEachOrdered (LongConsumer action)

Performs an action for each element of this stream, guaranteeing that each element is processed in encounter order for streams that have a defined encounter order.

This is a terminal operation.

Parameters
action LongConsumer: a non-interfering action to perform on the elements

generate

added in API level 24
public static LongStream generate (LongSupplier s)

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

Parameters
s LongSupplier: the LongSupplier for generated elements

Returns
LongStream a new infinite sequential unordered LongStream

iterate

added in API level 24
public static LongStream iterate (long seed, 
                LongUnaryOperator f)

Returns an infinite sequential ordered LongStream 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 LongStream 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.

Parameters
seed long: the initial element

f LongUnaryOperator: a function to be applied to to the previous element to produce a new element

Returns
LongStream a new sequential LongStream

iterator

added in API level 24
public abstract PrimitiveIterator.OfLong iterator ()

Returns an iterator for the elements of this stream.

This is a terminal operation.

Returns
PrimitiveIterator.OfLong the element iterator for this stream

limit

added in API level 24
public abstract LongStream limit (long maxSize)

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.

API Note:
  • While limit() is generally a cheap operation on sequential stream pipelines, it can be quite expensive on ordered parallel pipelines, especially for large values of maxSize, since limit(n) is constrained to return not just any n elements, but the first n elements in the encounter order. Using an unordered stream source (such as generate(LongSupplier)) or removing the ordering constraint with BaseStream.unordered() may result in significant speedups of limit() in parallel pipelines, if the semantics of your situation permit. If consistency with encounter order is required, and you are experiencing poor performance or memory utilization with limit() in parallel pipelines, switching to sequential execution with sequential() may improve performance.
Parameters
maxSize long: the number of elements the stream should be limited to

Returns
LongStream the new stream

Throws
IllegalArgumentException if maxSize is negative

map

added in API level 24
public abstract LongStream map (LongUnaryOperator mapper)

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

This is an intermediate operation.

Parameters
mapper LongUnaryOperator: a non-interfering, stateless function to apply to each element

Returns
LongStream the new stream

mapToDouble

added in API level 24
public abstract DoubleStream mapToDouble (LongToDoubleFunction mapper)

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 LongToDoubleFunction: a non-interfering, stateless function to apply to each element

Returns
DoubleStream the new stream

mapToInt

added in API level 24
public abstract IntStream mapToInt (LongToIntFunction mapper)

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 LongToIntFunction: a non-interfering, stateless function to apply to each element

Returns
IntStream the new stream

mapToObj

added in API level 24
public abstract Stream<U> mapToObj (LongFunction<? extends U> mapper)

Returns an object-valued Stream consisting of the results of applying the given function to the elements of this stream.

This is an intermediate operation.

Parameters
mapper LongFunction: a non-interfering, stateless function to apply to each element

Returns
Stream<U> the new stream

max

added in API level 24
public abstract OptionalLong max ()

Returns an OptionalLong describing the maximum element of this stream, or an empty optional if this stream is empty. This is a special case of a reduction and is equivalent to:

return reduce(Long::max);
 

This is a terminal operation.

Returns
OptionalLong an OptionalLong containing the maximum element of this stream, or an empty OptionalLong if the stream is empty

min

added in API level 24
public abstract OptionalLong min ()

Returns an OptionalLong describing the minimum element of this stream, or an empty optional if this stream is empty. This is a special case of a reduction and is equivalent to:

return reduce(Long::min);
 

This is a terminal operation.

Returns
OptionalLong an OptionalLong containing the minimum element of this stream, or an empty OptionalLong if the stream is empty

noneMatch

added in API level 24
public abstract boolean noneMatch (LongPredicate predicate)

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.

API Note:
  • This method evaluates the universal quantification of the negated predicate over the elements of the stream (for all x ~P(x)). If the stream is empty, the quantification is said to be vacuously satisfied and is always true, regardless of P(x).
Parameters
predicate LongPredicate: a non-interfering, stateless predicate to apply to elements of this stream

Returns
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
public static LongStream of (long... values)

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

Parameters
values long: the elements of the new stream

Returns
LongStream the new stream

of

added in API level 24
public static LongStream of (long t)

Returns a sequential LongStream containing a single element.

Parameters
t long: the single element

Returns
LongStream a singleton sequential stream

parallel

added in API level 24
public abstract LongStream 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.

Returns
LongStream a parallel stream

peek

added in API level 24
public abstract LongStream peek (LongConsumer action)

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.

API Note:
  • This method exists mainly to support debugging, where you want to see the elements as they flow past a certain point in a pipeline:
    LongStream.of(1, 2, 3, 4)
             .filter(e -> e > 2)
             .peek(e -> System.out.println("Filtered value: " + e))
             .map(e -> e * e)
             .peek(e -> System.out.println("Mapped value: " + e))
             .sum();
     
Parameters
action LongConsumer: a non-interfering action to perform on the elements as they are consumed from the stream

Returns
LongStream the new stream

range

added in API level 24
public static LongStream range (long startInclusive, 
                long endExclusive)

Returns a sequential ordered LongStream from startInclusive (inclusive) to endExclusive (exclusive) by an incremental step of 1.

API Note:
  • An equivalent sequence of increasing values can be produced sequentially using a for loop as follows:

    for (long i = startInclusive; i < endExclusive ; i++) { ... }
     
Parameters
startInclusive long: the (inclusive) initial value

endExclusive long: the exclusive upper bound

Returns
LongStream a sequential LongStream for the range of long elements

rangeClosed

added in API level 24
public static LongStream rangeClosed (long startInclusive, 
                long endInclusive)

Returns a sequential ordered LongStream from startInclusive (inclusive) to endInclusive (inclusive) by an incremental step of 1.

API Note:
  • An equivalent sequence of increasing values can be produced sequentially using a for loop as follows:

    for (long i = startInclusive; i <= endInclusive ; i++) { ... }
     
Parameters
startInclusive long: the (inclusive) initial value

endInclusive long: the inclusive upper bound

Returns
LongStream a sequential LongStream for the range of long elements

reduce

added in API level 24
public abstract OptionalLong reduce (LongBinaryOperator op)

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

boolean foundAny = false;
     long result = null;
     for (long element : this stream) {
         if (!foundAny) {
             foundAny = true;
             result = element;
         }
         else
             result = accumulator.applyAsLong(result, element);
     }
     return foundAny ? OptionalLong.of(result) : OptionalLong.empty();
 
but is not constrained to execute sequentially.

The accumulator function must be an associative function.

This is a terminal operation.

Parameters
op LongBinaryOperator: an associative, non-interfering, stateless function for combining two values

Returns
OptionalLong the result of the reduction

reduce

added in API level 24
public abstract long reduce (long identity, 
                LongBinaryOperator op)

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:

long result = identity;
     for (long element : this stream)
         result = accumulator.applyAsLong(result, element)
     return result;
 
but is not constrained to execute sequentially.

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

This is a terminal operation.

API Note:
  • Sum, min, max, and average are all special cases of reduction. Summing a stream of numbers can be expressed as:
    long sum = integers.reduce(0, (a, b) -> a+b);
     
    or more compactly:
    long sum = integers.reduce(0, Long::sum);
     

    While this may seem a more roundabout way to perform an aggregation compared to simply mutating a running total in a loop, reduction operations parallelize more gracefully, without needing additional synchronization and with greatly reduced risk of data races.

Parameters
identity long: the identity value for the accumulating function

op LongBinaryOperator: an associative, non-interfering, stateless function for combining two values

Returns
long the result of the reduction

sequential

added in API level 24
public abstract LongStream 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.

Returns
LongStream a sequential stream

skip

added in API level 24
public abstract LongStream skip (long n)

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.

API Note:
  • While skip() is generally a cheap operation on sequential stream pipelines, it can be quite expensive on ordered parallel pipelines, especially for large values of n, since skip(n) is constrained to skip not just any n elements, but the first n elements in the encounter order. Using an unordered stream source (such as generate(LongSupplier)) or removing the ordering constraint with BaseStream.unordered() may result in significant speedups of skip() in parallel pipelines, if the semantics of your situation permit. If consistency with encounter order is required, and you are experiencing poor performance or memory utilization with skip() in parallel pipelines, switching to sequential execution with sequential() may improve performance.
Parameters
n long: the number of leading elements to skip

Returns
LongStream the new stream

Throws
IllegalArgumentException if n is negative

sorted

added in API level 24
public abstract LongStream sorted ()

Returns a stream consisting of the elements of this stream in sorted order.

This is a stateful intermediate operation.

Returns
LongStream the new stream

spliterator

added in API level 24
public abstract Spliterator.OfLong spliterator ()

Returns a spliterator for the elements of this stream.

This is a terminal operation.

Returns
Spliterator.OfLong the element spliterator for this stream

sum

added in API level 24
public abstract long sum ()

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

return reduce(0, Long::sum);
 

This is a terminal operation.

Returns
long the sum of elements in this stream

summaryStatistics

added in API level 24
public abstract LongSummaryStatistics summaryStatistics ()

Returns a LongSummaryStatistics describing various summary data about the elements of this stream. This is a special case of a reduction.

This is a terminal operation.

Returns
LongSummaryStatistics a LongSummaryStatistics describing various summary data about the elements of this stream

toArray

added in API level 24
public abstract long[] toArray ()

Returns an array containing the elements of this stream.

This is a terminal operation.

Returns
long[] an array containing the elements of this stream