Interface LongStream
-
- All Superinterfaces:
- AutoCloseable, BaseStream<Long,LongStream>
public interface LongStream extends BaseStream<Long,LongStream>
A sequence of primitive long-valued elements supporting sequential and parallel aggregate operations. This is thelong
primitive specialization ofStream
.The following example illustrates an aggregate operation using
Stream
andLongStream
, computing the sum of the weights of the red widgets:
See the class documentation forlong sum = widgets.stream() .filter(w -> w.getColor() == RED) .mapToLong(w -> w.getWeight()) .sum();
Stream
and the package documentation for java.util.stream for additional specification of streams, stream operations, stream pipelines, and parallelism.- Since:
- 1.8
- See Also:
-
Stream
, java.util.stream
-
-
Nested Class Summary
Nested Classes Modifier and Type Interface and Description static interface
LongStream.Builder
A mutable builder for aLongStream
.
-
Method Summary
All Methods Static Methods Instance Methods Abstract Methods Default Methods Modifier and Type Method and Description boolean
allMatch(LongPredicate predicate)
Returns whether all elements of this stream match the provided predicate.boolean
anyMatch(LongPredicate predicate)
Returns whether any elements of this stream match the provided predicate.DoubleStream
asDoubleStream()
Returns aDoubleStream
consisting of the elements of this stream, converted todouble
.OptionalDouble
average()
Returns anOptionalDouble
describing the arithmetic mean of elements of this stream, or an empty optional if this stream is empty.Stream<Long>
boxed()
Returns aStream
consisting of the elements of this stream, each boxed to aLong
.static LongStream.Builder
builder()
Returns a builder for aLongStream
.<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.long
count()
Returns the count of elements in this stream.LongStream
distinct()
Returns a stream consisting of the distinct elements of this stream.static LongStream
empty()
Returns an empty sequentialLongStream
.LongStream
filter(LongPredicate predicate)
Returns a stream consisting of the elements of this stream that match the given predicate.OptionalLong
findAny()
Returns anOptionalLong
describing some element of the stream, or an emptyOptionalLong
if the stream is empty.OptionalLong
findFirst()
Returns anOptionalLong
describing the first element of this stream, or an emptyOptionalLong
if the stream is empty.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.void
forEach(LongConsumer action)
Performs an action for each element of this stream.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 providedLongSupplier
.static LongStream
iterate(long seed, LongUnaryOperator f)
Returns an infinite sequential orderedLongStream
produced by iterative application of a functionf
to an initial elementseed
, producing aStream
consisting ofseed
,f(seed)
,f(f(seed))
, etc.PrimitiveIterator.OfLong
iterator()
Returns an iterator for the elements of this stream.LongStream
limit(long maxSize)
Returns a stream consisting of the elements of this stream, truncated to be no longer thanmaxSize
in length.LongStream
map(LongUnaryOperator mapper)
Returns a stream consisting of the results of applying the given function to the elements of this stream.DoubleStream
mapToDouble(LongToDoubleFunction mapper)
Returns aDoubleStream
consisting of the results of applying the given function to the elements of this stream.IntStream
mapToInt(LongToIntFunction mapper)
Returns anIntStream
consisting of the results of applying the given function to the elements of this stream.<U> Stream<U>
mapToObj(LongFunction<? extends U> mapper)
Returns an object-valuedStream
consisting of the results of applying the given function to the elements of this stream.OptionalLong
max()
Returns anOptionalLong
describing the maximum element of this stream, or an empty optional if this stream is empty.OptionalLong
min()
Returns anOptionalLong
describing the minimum element of this stream, or an empty optional if this stream is empty.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 sequentialLongStream
containing a single element.LongStream
parallel()
Returns an equivalent stream that is parallel.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 orderedLongStream
fromstartInclusive
(inclusive) toendExclusive
(exclusive) by an incremental step of1
.static LongStream
rangeClosed(long startInclusive, long endInclusive)
Returns a sequential orderedLongStream
fromstartInclusive
(inclusive) toendInclusive
(inclusive) by an incremental step of1
.OptionalLong
reduce(LongBinaryOperator op)
Performs a reduction on the elements of this stream, using an associative accumulation function, and returns anOptionalLong
describing the reduced value, if any.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.LongStream
sequential()
Returns an equivalent stream that is sequential.LongStream
skip(long n)
Returns a stream consisting of the remaining elements of this stream after discarding the firstn
elements of the stream.LongStream
sorted()
Returns a stream consisting of the elements of this stream in sorted order.Spliterator.OfLong
spliterator()
Returns a spliterator for the elements of this stream.long
sum()
Returns the sum of elements in this stream.LongSummaryStatistics
summaryStatistics()
Returns aLongSummaryStatistics
describing various summary data about the elements of this stream.long[]
toArray()
Returns an array containing the elements of this stream.-
Methods inherited from interface java.util.stream.BaseStream
close, isParallel, onClose, unordered
-
-
-
-
Method Detail
filter
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
map
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
mapToObj
<U> Stream<U> mapToObj(LongFunction<? extends U> mapper)
Returns an object-valuedStream
consisting of the results of applying the given function to the elements of this stream.This is an intermediate operation.
- Type Parameters:
-
U
- the element type of the new stream - Parameters:
-
mapper
- a non-interfering, stateless function to apply to each element - Returns:
- the new stream
mapToInt
IntStream mapToInt(LongToIntFunction mapper)
Returns anIntStream
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
mapToDouble
DoubleStream mapToDouble(LongToDoubleFunction mapper)
Returns aDoubleStream
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
flatMap
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 isclosed
after its contents have been placed into this stream. (If a mapped stream isnull
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 aLongStream
of new values - Returns:
- the new stream
- See Also:
-
Stream.flatMap(Function)
distinct
LongStream distinct()
Returns a stream consisting of the distinct elements of this stream.This is a stateful intermediate operation.
- Returns:
- the new stream
sorted
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
peek
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
- a non-interfering action to perform on the elements as they are consumed from the stream - Returns:
- the new stream
limit
LongStream limit(long maxSize)
Returns a stream consisting of the elements of this stream, truncated to be no longer thanmaxSize
in length.- 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 ofmaxSize
, sincelimit(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 asgenerate(LongSupplier)
) or removing the ordering constraint withBaseStream.unordered()
may result in significant speedups oflimit()
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 withlimit()
in parallel pipelines, switching to sequential execution withsequential()
may improve performance. - Parameters:
-
maxSize
- the number of elements the stream should be limited to - Returns:
- the new stream
- Throws:
-
IllegalArgumentException
- ifmaxSize
is negative
skip
LongStream skip(long n)
Returns a stream consisting of the remaining elements of this stream after discarding the firstn
elements of the stream. If this stream contains fewer thann
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 ofn
, sinceskip(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 asgenerate(LongSupplier)
) or removing the ordering constraint withBaseStream.unordered()
may result in significant speedups ofskip()
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 withskip()
in parallel pipelines, switching to sequential execution withsequential()
may improve performance. - Parameters:
-
n
- the number of leading elements to skip - Returns:
- the new stream
- Throws:
-
IllegalArgumentException
- ifn
is negative
forEach
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
forEachOrdered
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:
-
forEach(LongConsumer)
toArray
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
reduce
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:
but is not constrained to execute sequentially.long result = identity; for (long element : this stream) result = accumulator.applyAsLong(result, element) return result;
The
identity
value must be an identity for the accumulator function. This means that for allx
,accumulator.apply(identity, x)
is equal tox
. Theaccumulator
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:
or more compactly:long sum = integers.reduce(0, (a, b) -> a+b);
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
- 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:
-
sum()
,min()
,max()
,average()
reduce
OptionalLong reduce(LongBinaryOperator op)
Performs a reduction on the elements of this stream, using an associative accumulation function, and returns anOptionalLong
describing the reduced value, if any. This is equivalent to:
but is not constrained to execute sequentially.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();
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:
-
reduce(long, LongBinaryOperator)
collect
<R> 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 anArrayList
, 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.
- Type Parameters:
-
R
- type of the result - 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:
-
Stream.collect(Supplier, BiConsumer, BiConsumer)
sum
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
min
OptionalLong min()
Returns anOptionalLong
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 emptyOptionalLong
if the stream is empty
max
OptionalLong max()
Returns anOptionalLong
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 emptyOptionalLong
if the stream is empty
count
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
average
OptionalDouble average()
Returns anOptionalDouble
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
summaryStatistics
LongSummaryStatistics summaryStatistics()
Returns aLongSummaryStatistics
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
anyMatch
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 thenfalse
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
- a non-interfering, stateless predicate to apply to elements of this stream - Returns:
-
true
if any elements of the stream match the provided predicate, otherwisefalse
allMatch
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 thentrue
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
- 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, otherwisefalse
noneMatch
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 thentrue
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
- 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, otherwisefalse
findFirst
OptionalLong findFirst()
Returns anOptionalLong
describing the first element of this stream, or an emptyOptionalLong
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 emptyOptionalLong
if the stream is empty
findAny
OptionalLong findAny()
Returns anOptionalLong
describing some element of the stream, or an emptyOptionalLong
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 emptyOptionalLong
if the stream is empty - See Also:
-
findFirst()
asDoubleStream
DoubleStream asDoubleStream()
Returns aDoubleStream
consisting of the elements of this stream, converted todouble
.This is an intermediate operation.
- Returns:
-
a
DoubleStream
consisting of the elements of this stream, converted todouble
boxed
Stream<Long> boxed()
Returns aStream
consisting of the elements of this stream, each boxed to aLong
.This is an intermediate operation.
- Returns:
-
a
Stream
consistent of the elements of this stream, each boxed toLong
sequential
LongStream sequential()
Description copied from interface:BaseStream
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.
- Specified by:
-
sequential
in interfaceBaseStream<Long,LongStream>
- Returns:
- a sequential stream
parallel
LongStream parallel()
Description copied from interface:BaseStream
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.
- Specified by:
-
parallel
in interfaceBaseStream<Long,LongStream>
- Returns:
- a parallel stream
iterator
PrimitiveIterator.OfLong iterator()
Description copied from interface:BaseStream
Returns an iterator for the elements of this stream.This is a terminal operation.
- Specified by:
-
iterator
in interfaceBaseStream<Long,LongStream>
- Returns:
- the element iterator for this stream
spliterator
Spliterator.OfLong spliterator()
Description copied from interface:BaseStream
Returns a spliterator for the elements of this stream.This is a terminal operation.
- Specified by:
-
spliterator
in interfaceBaseStream<Long,LongStream>
- Returns:
- the element spliterator for this stream
builder
static LongStream.Builder builder()
Returns a builder for aLongStream
.- Returns:
- a stream builder
empty
static LongStream empty()
Returns an empty sequentialLongStream
.- Returns:
- an empty sequential stream
of
static LongStream of(long t)
Returns a sequentialLongStream
containing a single element.- Parameters:
-
t
- the single element - Returns:
- a singleton sequential stream
of
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
iterate
static LongStream iterate(long seed, LongUnaryOperator f)
Returns an infinite sequential orderedLongStream
produced by iterative application of a functionf
to an initial elementseed
, producing aStream
consisting ofseed
,f(seed)
,f(f(seed))
, etc.The first element (position
0
) in theLongStream
will be the providedseed
. Forn > 0
, the element at positionn
, will be the result of applying the functionf
to the element at positionn - 1
.- Parameters:
-
seed
- the initial element -
f
- a function to be applied to the previous element to produce a new element - Returns:
-
a new sequential
LongStream
generate
static LongStream generate(LongSupplier s)
Returns an infinite sequential unordered stream where each element is generated by the providedLongSupplier
. This is suitable for generating constant streams, streams of random elements, etc.- Parameters:
-
s
- theLongSupplier
for generated elements - Returns:
-
a new infinite sequential unordered
LongStream
range
static LongStream range(long startInclusive, long endExclusive)
Returns a sequential orderedLongStream
fromstartInclusive
(inclusive) toendExclusive
(exclusive) by an incremental step of1
.- 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
- the (inclusive) initial value -
endExclusive
- the exclusive upper bound - Returns:
-
a sequential
LongStream
for the range oflong
elements
rangeClosed
static LongStream rangeClosed(long startInclusive, long endInclusive)
Returns a sequential orderedLongStream
fromstartInclusive
(inclusive) toendInclusive
(inclusive) by an incremental step of1
.- 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
- the (inclusive) initial value -
endInclusive
- the inclusive upper bound - Returns:
-
a sequential
LongStream
for the range oflong
elements
concat
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
- the first stream -
b
- the second stream - Returns:
- the concatenation of the two input streams
-
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