LongStream

public interface LongStream implements BaseStream<Long, 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.

See Also

Nested Class Summary

interface LongStream.Builder A mutable builder for a LongStream. 

Public Method Summary

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 Method Summary

Public Methods

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.

Parameters
predicate a non-interfering, stateless predicate to apply to elements of this stream
Returns
  • true if either all elements of the stream match the provided predicate or the stream is empty, otherwise false

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.

Parameters
predicate a non-interfering, stateless predicate to apply to elements of this stream
Returns
  • true if any elements of the stream match the provided predicate, otherwise false

public abstract DoubleStream asDoubleStream ()

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

This is an intermediate operation.

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

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

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
  • a Stream consistent of the elements of this stream, each boxed to Long

public static LongStream.Builder builder ()

Returns a builder for a LongStream.

Returns
  • a stream builder

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 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 an associative, non-interfering, stateless function for incorporating an additional element into a result
combiner an associative, non-interfering, stateless function for combining two values, which must be compatible with the accumulator function
Returns
  • the result of the reduction
See Also

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.

Parameters
a the first stream
b the second stream
Returns
  • the concatenation of the two input streams

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
  • the count of elements in this stream

public abstract LongStream distinct ()

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

This is a stateful intermediate operation.

Returns
  • the new stream

public static LongStream empty ()

Returns an empty sequential LongStream.

Returns
  • an empty sequential stream

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 a non-interfering, stateless predicate to apply to each element to determine if it should be included
Returns
  • the new stream

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
  • an OptionalLong describing some element of this stream, or an empty OptionalLong if the stream is empty
See Also

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

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 a non-interfering, stateless function to apply to each element which produces a LongStream of new values
Returns
  • the new stream
See Also

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 a non-interfering action to perform on the elements

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 a non-interfering action to perform on the elements
See Also

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 the LongSupplier for generated elements
Returns
  • a new infinite sequential unordered LongStream

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 the initial element
f a function to be applied to to the previous element to produce a new element
Returns
  • a new sequential LongStream

public abstract PrimitiveIterator.OfLong iterator ()

Returns an iterator for the elements of this stream.

This is a terminal operation.

Returns
  • the element iterator for this stream

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.

Parameters
maxSize the number of elements the stream should be limited to
Returns
  • the new stream
Throws
IllegalArgumentException if maxSize is negative

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 a non-interfering, stateless function to apply to each element
Returns
  • the new stream

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 a non-interfering, stateless function to apply to each element
Returns
  • the new stream

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 a non-interfering, stateless function to apply to each element
Returns
  • the new stream

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 a non-interfering, stateless function to apply to each element
Returns
  • the new stream

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

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

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.

Parameters
predicate a non-interfering, stateless predicate to apply to elements of this stream
Returns
  • true if either no elements of the stream match the provided predicate or the stream is empty, otherwise false

public static LongStream of (long... values)

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

Parameters
values the elements of the new stream
Returns
  • the new stream

public static LongStream of (long t)

Returns a sequential LongStream containing a single element.

Parameters
t the single element
Returns
  • a singleton sequential stream

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
  • a parallel stream

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.

Parameters
action a non-interfering action to perform on the elements as they are consumed from the stream
Returns
  • the new stream

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.

Parameters
startInclusive the (inclusive) initial value
endExclusive the exclusive upper bound
Returns
  • a sequential LongStream for the range of long elements

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.

Parameters
startInclusive the (inclusive) initial value
endInclusive the inclusive upper bound
Returns
  • a sequential LongStream for the range of long elements

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 an associative, non-interfering, stateless function for combining two values
Returns
  • the result of the reduction
See Also

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.

Parameters
identity the identity value for the accumulating function
op an associative, non-interfering, stateless function for combining two values
Returns
  • the result of the reduction
See Also

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
  • a sequential stream

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.

Parameters
n the number of leading elements to skip
Returns
  • the new stream
Throws
IllegalArgumentException if n is negative

public abstract LongStream sorted ()

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

This is a stateful intermediate operation.

Returns
  • the new stream

public abstract Spliterator.OfLong spliterator ()

Returns a spliterator for the elements of this stream.

This is a terminal operation.

Returns
  • the element spliterator for this stream

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
  • the sum of elements in this stream

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

public abstract long[] toArray ()

Returns an array containing the elements of this stream.

This is a terminal operation.

Returns
  • an array containing the elements of this stream