Java stream api boxed

Java stream api boxed

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.stream for additional specification of streams, stream operations, stream pipelines, and parallelism.

Nested Class Summary

Method Summary

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

Creates a lazily concatenated stream whose elements are all the elements of the first stream followed by all the elements of the second stream.

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.

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 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 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.

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.

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 .

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

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

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

Methods inherited from interface java.util.stream.BaseStream

Method Detail

filter

IntStream filter(IntPredicate predicate)

Returns a stream consisting of the elements of this stream that match the given predicate. This is an intermediate operation.

map

IntStream map(IntUnaryOperator mapper)

Returns a stream consisting of the results of applying the given function to the elements of this stream. This is an intermediate operation.

mapToObj

 Stream mapToObj(IntFunction 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.

mapToLong

LongStream mapToLong(IntToLongFunction mapper)

Returns a LongStream consisting of the results of applying the given function to the elements of this stream. This is an intermediate operation.

mapToDouble

DoubleStream mapToDouble(IntToDoubleFunction mapper)

Returns a DoubleStream consisting of the results of applying the given function to the elements of this stream. This is an intermediate operation.

flatMap

IntStream flatMap(IntFunction 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.

distinct

Returns a stream consisting of the distinct elements of this stream. This is a stateful intermediate operation.

sorted

Returns a stream consisting of the elements of this stream in sorted order. This is a stateful intermediate operation.

peek

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:

 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(); 

limit

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.

skip

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.

forEach

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.

forEachOrdered

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.

toArray

reduce

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:

 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.

API Note: Sum, min, max, and average are all special cases of reduction. Summing a stream of numbers can be expressed as:

 int sum = integers.reduce(0, (a, b) -> a+b); 

 int sum = integers.reduce(0, Integer::sum); 

reduce

OptionalInt reduce(IntBinaryOperator op)

Performs a reduction on the elements of this stream, using an associative accumulation 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.

collect

 R collect(Supplier supplier, ObjIntConsumer accumulator, BiConsumer 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 (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.

sum

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

 return reduce(0, Integer::sum); 

min

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 reduction and is equivalent to:

max

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 reduction and is equivalent to:

count

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

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.

summaryStatistics

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.

anyMatch

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.

allMatch

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.

noneMatch

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.

findFirst

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.

findAny

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.)

asLongStream

Returns a LongStream consisting of the elements of this stream, converted to long . This is an intermediate operation.

asDoubleStream

Returns a DoubleStream consisting of the elements of this stream, converted to double . This is an intermediate operation.

boxed

Returns a Stream consisting of the elements of this stream, each boxed to an Integer . This is an intermediate operation.

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.

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.

iterator

spliterator

builder

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