AutoCloseable, BaseStream<Integer,IntStream>
A sequence of primitive int-valued elements supporting sequential and parallel aggregate operations. This is the
int
primitive specialization of
Stream
.
The following example illustrates an aggregate operation using Stream and IntStream, computing the sum of the weights of the red widgets:
int sum = widgets.stream()
.filter(w -> w.getColor() == RED)
.mapToInt(w -> w.getWeight())
.sum();
See the class documentation for
Stream
and the package documentation for
java.util.streamfor additional specification of streams, stream operations, stream pipelines, and parallelism.
Nested Classes
static interface
A mutable builder for an IntStream.
static interface
Represents an operation that accepts an int-valued argument and an IntConsumer, and returns no result.
boolean
Returns whether all elements of this stream match the provided predicate.
boolean
Returns whether any elements of this stream match the provided predicate.
Returns a DoubleStream consisting of the elements of this stream, converted to double.
Returns a LongStream consisting of the elements of this stream, converted to long.
Returns an OptionalDouble describing the arithmetic mean of elements of this stream, or an empty optional if this stream is empty.
Returns a Stream consisting of the elements of this stream, each boxed to an Integer.
Returns a builder for an IntStream.
<R> R
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
Returns the count of elements in this stream.
Returns a stream consisting of the distinct elements of this stream.
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.
Returns an empty sequential IntStream.
Returns a stream consisting of the elements of this stream that match the given predicate.
Returns an
OptionalInt
describing some element of the stream, or an empty
OptionalInt
if the stream is empty.
Returns an
OptionalInt
describing the first element of this stream, or an empty
OptionalInt
if the stream is empty.
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
Performs an action for each element of this stream.
void
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.
Returns an infinite sequential unordered stream where each element is generated by the provided IntSupplier.
Returns a sequential ordered IntStream produced by iterative application of the given next function to an initial element, conditioned on satisfying the given hasNext predicate.
Returns an infinite sequential ordered IntStream 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.
Returns a stream consisting of the elements of this stream, truncated to be no longer than maxSize in length.
Returns a stream consisting of the results of applying the given function to the elements of this stream.
Returns a stream consisting of the results of replacing each element of this stream with multiple elements, specifically zero or more elements.
Returns a DoubleStream consisting of the results of applying the given function to the elements of this stream.
Returns a LongStream consisting of the results of applying the given function to the elements of this stream.
Returns an object-valued Stream consisting of the results of applying the given function to the elements of this stream.
Returns an OptionalInt describing the maximum element of this stream, or an empty optional if this stream is empty.
Returns an OptionalInt describing the minimum element of this stream, or an empty optional if this stream is empty.
boolean
Returns whether no elements of this stream match the provided predicate.
Returns a sequential IntStream containing a single element.
Returns a sequential ordered stream whose elements are the specified values.
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.
range(int startInclusive, int endExclusive)
Returns a sequential ordered IntStream from startInclusive (inclusive) to endExclusive (exclusive) by an incremental step of 1.
Returns a sequential ordered IntStream from startInclusive (inclusive) to endInclusive (inclusive) by an incremental step of 1.
int
Performs a
reductionon the elements of this stream, using the provided identity value and an
associativeaccumulation function, and returns the reduced value.
Performs a
reductionon the elements of this stream, using an
associativeaccumulation function, and returns an
OptionalInt
describing the reduced value, if any.
Returns a stream consisting of the remaining elements of this stream after discarding the first n elements of the stream.
Returns a stream consisting of the elements of this stream in sorted order.
int
Returns the sum of elements in this stream.
Returns an IntSummaryStatistics describing various summary data about the elements of this stream.
Returns, if this stream is ordered, a stream consisting of the longest prefix of elements taken from this stream that match the given predicate.
int[]
Returns an array containing the elements of this stream.
This is an intermediate operation.
predicate - a non-interfering, stateless predicate to apply to each element to determine if it should be included
This is an intermediate operation.
mapper - a non-interfering, stateless function to apply to each element
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.
U - the element type of the new stream
mapper - a non-interfering, stateless function to apply to each element
Returns a
LongStream
consisting of the results of applying the given function to the elements of this stream.
This is an intermediate operation.
mapper - a non-interfering, stateless function to apply to each element
Returns a
DoubleStream
consisting of the results of applying the given function to the elements of this stream.
This is an intermediate operation.
mapper - a non-interfering, stateless function to apply to each element
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.
mapper - a non-interfering, stateless function to apply to each element which produces an IntStream of new values
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
consumerargument 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.
flatMap on this stream, passing a function that behaves as follows. First, it calls the mapper function with an IntConsumer that accumulates replacement elements into a newly created internal buffer. When the mapper function returns, it creates an IntStream from the internal buffer. Finally, it returns this stream to flatMap.
mapper - a non-interfering, stateless function that generates replacement elements
This is a stateful intermediate operation.
This is a stateful intermediate operation.
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.
IntStream.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();
In cases where the stream implementation is able to optimize away the production of some or all the elements (such as with short-circuiting operations like findFirst, or in the example described in count()), the action will not be invoked for those elements.
action - a non-interfering action to perform on the elements as they are consumed from the stream
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(IntSupplier)) 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 BaseStream.sequential() may improve performance.
maxSize - the number of elements the stream should be limited to
IllegalArgumentException - if maxSize is negative
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.
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(IntSupplier)) 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 BaseStream.sequential() may improve performance.
n - the number of leading elements to skip
IllegalArgumentException - if n is negative
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 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 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.
takeWhile() is generally a cheap operation on sequential stream pipelines, it can be quite expensive on ordered parallel pipelines, since the operation is constrained to return not just any valid prefix, but the longest prefix of elements in the encounter order. Using an unordered stream source (such as generate(IntSupplier)) or removing the ordering constraint with BaseStream.unordered() may result in significant speedups of takeWhile() 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 takeWhile() in parallel pipelines, switching to sequential execution with BaseStream.sequential() may improve performance.
spliterator of this stream, wraps that spliterator so as to support the semantics of this operation on traversal, and returns a new stream associated with the wrapped spliterator. The returned stream preserves the execution characteristics of this stream (namely parallel or sequential execution as per BaseStream.isParallel()) but the wrapped spliterator may choose to not support splitting. When the returned stream is closed, the close handlers for both the returned and this stream are invoked.
predicate - a non-interfering, stateless predicate to apply to elements to determine the longest prefix of elements.
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.
dropWhile() is generally a cheap operation on sequential stream pipelines, it can be quite expensive on ordered parallel pipelines, since the operation is constrained to return not just any valid prefix, but the longest prefix of elements in the encounter order. Using an unordered stream source (such as generate(IntSupplier)) or removing the ordering constraint with BaseStream.unordered() may result in significant speedups of dropWhile() 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 dropWhile() in parallel pipelines, switching to sequential execution with BaseStream.sequential() may improve performance.
spliterator of this stream, wraps that spliterator so as to support the semantics of this operation on traversal, and returns a new stream associated with the wrapped spliterator. The returned stream preserves the execution characteristics of this stream (namely parallel or sequential execution as per BaseStream.isParallel()) but the wrapped spliterator may choose to not support splitting. When the returned stream is closed, the close handlers for both the returned and this stream are invoked.
predicate - a non-interfering, stateless predicate to apply to elements to determine the longest prefix of elements.
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.
action - a non-interfering action to perform on the elements
This is a terminal operation.
action - a non-interfering action to perform on the elements
int[] toArray()
This is a terminal operation.
Performs a
reductionon the elements of this stream, using the provided identity value and an
associativeaccumulation function, and returns the reduced value. This is equivalent to:
int result = identity;
for (int element : this stream)
result = accumulator.applyAsInt(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.
int sum = integers.reduce(0, (a, b) -> a+b);
int sum = integers.reduce(0, Integer::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.
identity - the identity value for the accumulating function
op - an associative, non-interfering, stateless function for combining two values
Performs a
reductionon the elements of this stream, using an
associativeaccumulation function, and returns an
OptionalInt
describing the reduced value, if any. This is equivalent to:
boolean foundAny = false;
int result = null;
for (int element : this stream) {
if (!foundAny) {
foundAny = true;
result = element;
}
else
result = accumulator.applyAsInt(result, element);
}
return foundAny ? OptionalInt.of(result) : OptionalInt.empty();
but is not constrained to execute sequentially.
The accumulator function must be an associative function.
This is a terminal operation.
op - an associative, non-interfering, stateless function for combining two values
Performs a
mutable reductionoperation 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 (int element : this stream)
accumulator.accept(result, element);
return result;
Like reduce(int, IntBinaryOperator), collect operations can be parallelized without requiring additional synchronization.
This is a terminal operation.
R - the type of the mutable result container
supplier - 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 - an associative, non-interfering, stateless function that must fold an element into a result container.
combiner - 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.
int sum()
Returns the sum of elements in this stream. This is a special case of a
reductionand is equivalent to:
return reduce(0, Integer::sum);
This is a terminal operation.
Returns an
OptionalInt
describing the minimum element of this stream, or an empty optional if this stream is empty. This is a special case of a
reductionand is equivalent to:
return reduce(Integer::min);
This is a terminal operation.
OptionalInt containing the minimum element of this stream, or an empty OptionalInt if the stream is empty
Returns an
OptionalInt
describing the maximum element of this stream, or an empty optional if this stream is empty. This is a special case of a
reductionand is equivalent to:
return reduce(Integer::max);
This is a terminal operation.
OptionalInt containing the maximum element of this stream, or an empty OptionalInt if the stream is empty
long count()
Returns the count of elements in this stream. This is a special case of a
reductionand is equivalent to:
return mapToLong(e -> 1L).sum();
This is a terminal operation.
IntStream s = IntStream.of(1, 2, 3, 4);
long count = s.peek(System.out::println).count();
peek, does not inject into or remove elements from the stream (as may be the case for flatMap or filter operations). Thus the count is 4 and there is no need to execute the pipeline and, as a side-effect, print out the elements.
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.
OptionalDouble containing the average element of this stream, or an empty optional if the stream is empty
Returns an
IntSummaryStatistics
describing various summary data about the elements of this stream. This is a special case of a
reduction.
This is a terminal operation.
IntSummaryStatistics describing various summary data about the elements of this stream
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.
predicate - a non-interfering, stateless predicate to apply to elements of this stream
true if any elements of the stream match the provided predicate, otherwise false
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.
true (regardless of P(x)).
predicate - a non-interfering, stateless predicate to apply to elements of this stream
true if either all elements of the stream match the provided predicate or the stream is empty, otherwise false
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.
true, regardless of P(x).
predicate - a non-interfering, stateless predicate to apply to elements of this stream
true if either no elements of the stream match the provided predicate or the stream is empty, otherwise false
Returns an
OptionalInt
describing the first element of this stream, or an empty
OptionalInt
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.
OptionalInt describing the first element of this stream, or an empty OptionalInt if the stream is empty
Returns an
OptionalInt
describing some element of the stream, or an empty
OptionalInt
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.)
OptionalInt describing some element of this stream, or an empty OptionalInt if the stream is empty
Returns a
LongStream
consisting of the elements of this stream, converted to
long
.
This is an intermediate operation.
LongStream consisting of the elements of this stream, converted to long
Returns a
DoubleStream
consisting of the elements of this stream, converted to
double
.
This is an intermediate operation.
DoubleStream consisting of the elements of this stream, converted to double
Returns a
Stream
consisting of the elements of this stream, each boxed to an
Integer
.
This is an intermediate operation.
Stream consistent of the elements of this stream, each boxed to an Integer
Returns a builder for an IntStream.
Returns an empty sequential IntStream.
Returns a sequential IntStream containing a single element.
t - the single element
Returns a sequential ordered stream whose elements are the specified values.
values - the elements of the new stream
Returns an infinite sequential ordered
IntStream
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 IntStream 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.
seed - the initial element
f - a function to be applied to the previous element to produce a new element
IntStream
Returns a sequential ordered
IntStream
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.
IntStream.iterate should produce the same sequence of elements as produced by the corresponding for-loop:
for (int index=seed; hasNext.test(index); index = next.applyAsInt(index)) {
...
}
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.
seed - the initial element
hasNext - a predicate to apply to elements to determine when the stream must terminate.
next - a function to be applied to the previous element to produce a new element
IntStream
Returns an infinite sequential unordered stream where each element is generated by the provided IntSupplier. This is suitable for generating constant streams, streams of random elements, etc.
s - the IntSupplier for generated elements
IntStream
Returns a sequential ordered IntStream from startInclusive (inclusive) to endExclusive (exclusive) by an incremental step of 1.
An equivalent sequence of increasing values can be produced sequentially using a for loop as follows:
for (int i = startInclusive; i < endExclusive ; i++) { ... }
startInclusive - the (inclusive) initial value
endExclusive - the exclusive upper bound
IntStream for the range of int elements
Returns a sequential ordered IntStream from startInclusive (inclusive) to endInclusive (inclusive) by an incremental step of 1.
An equivalent sequence of increasing values can be produced sequentially using a for loop as follows:
for (int i = startInclusive; i <= endInclusive ; i++) { ... }
startInclusive - the (inclusive) initial value
endInclusive - the inclusive upper bound
IntStream for the range of int elements
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.
IntStream concat = Stream.of(s1, s2, s3, s4).flatMapToInt(s -> s);
StackOverflowError.
a - the first stream
b - the second stream
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