public interface DoubleStream extends BaseStream<Double,DoubleStream>
A sequence of primitive double-valued elements supporting sequential and parallel aggregate operations. This is the double primitive specialization of Stream.
The following example illustrates an aggregate operation using Stream and DoubleStream, computing the sum of the weights of the red widgets:
double sum = widgets.stream()
.filter(w -> w.getColor() == RED)
.mapToDouble(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.Stream, java.util.stream
| Modifier and Type | Interface and Description |
|---|---|
static interface |
DoubleStream.Builder A mutable builder for a |
DoubleStream filter(DoublePredicate predicate)
Returns a stream consisting of the elements of this stream that match the given predicate.
This is an intermediate operation.
predicate - a non-interfering, stateless predicate to apply to each element to determine if it should be includedDoubleStream map(DoubleUnaryOperator mapper)
Returns a stream 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<U> Stream<U> mapToObj(DoubleFunction<? 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.
U - the element type of the new streammapper - a non-interfering, stateless function to apply to each elementIntStream mapToInt(DoubleToIntFunction mapper)
Returns an IntStream 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 elementLongStream mapToLong(DoubleToLongFunction mapper)
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 elementDoubleStream flatMap(DoubleFunction<? extends DoubleStream> 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.
mapper - a non-interfering, stateless function to apply to each element which produces a DoubleStream of new valuesStream.flatMap(Function)DoubleStream distinct()
Returns a stream consisting of the distinct elements of this stream. The elements are compared for equality according to Double.compare(double, double).
This is a stateful intermediate operation.
DoubleStream sorted()
Returns a stream consisting of the elements of this stream in sorted order. The elements are compared for equality according to Double.compare(double, double).
This is a stateful intermediate operation.
DoubleStream peek(DoubleConsumer 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.
DoubleStream.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();
action - a non-interfering action to perform on the elements as they are consumed from the streamDoubleStream limit(long maxSize)
Returns a stream consisting of the elements of this stream, truncated to be no longer than maxSize in length.
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(DoubleSupplier)) or removing the ordering constraint with BaseStream.unordered() may result in significant speedups of limit() in parallel pipelines, if the semantics of your situation permit. If consistency with encounter order is required, and you are experiencing poor performance or memory utilization with limit() in parallel pipelines, switching to sequential execution with sequential() may improve performance.maxSize - the number of elements the stream should be limited toIllegalArgumentException - if maxSize is negativeDoubleStream 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.
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(DoubleSupplier)) or removing the ordering constraint with BaseStream.unordered() may result in significant speedups of skip() in parallel pipelines, if the semantics of your situation permit. If consistency with encounter order is required, and you are experiencing poor performance or memory utilization with skip() in parallel pipelines, switching to sequential execution with sequential() may improve performance.n - the number of leading elements to skipIllegalArgumentException - if n is negativevoid forEach(DoubleConsumer 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.
action - a non-interfering action to perform on the elementsvoid forEachOrdered(DoubleConsumer 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.
action - a non-interfering action to perform on the elementsforEach(DoubleConsumer)double[] toArray()
Returns an array containing the elements of this stream.
This is a terminal operation.
double reduce(double identity,
DoubleBinaryOperator 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:
double result = identity;
for (double element : this stream)
result = accumulator.applyAsDouble(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.
double sum = numbers.reduce(0, (a, b) -> a+b);or more compactly:
double sum = numbers.reduce(0, Double::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 functionop - an associative, non-interfering, stateless function for combining two valuessum(), min(), max(), average()
OptionalDouble reduce(DoubleBinaryOperator op)
Performs a reduction on the elements of this stream, using an associative accumulation function, and returns an OptionalDouble describing the reduced value, if any. This is equivalent to:
boolean foundAny = false;
double result = null;
for (double element : this stream) {
if (!foundAny) {
foundAny = true;
result = element;
}
else
result = accumulator.applyAsDouble(result, element);
}
return foundAny ? OptionalDouble.of(result) : OptionalDouble.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 valuesreduce(double, DoubleBinaryOperator)<R> R collect(Supplier<R> supplier,
ObjDoubleConsumer<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 (double element : this stream)
accumulator.accept(result, element);
return result;
Like reduce(double, DoubleBinaryOperator), collect operations can be parallelized without requiring additional synchronization.
This is a terminal operation.
R - type of the resultsupplier - 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 resultcombiner - an associative, non-interfering, stateless function for combining two values, which must be compatible with the accumulator functionStream.collect(Supplier, BiConsumer, BiConsumer)double sum()
Returns the sum of elements in this stream. Summation is a special case of a reduction. If floating-point summation were exact, this method would be equivalent to:
return reduce(0, Double::sum);However, since floating-point summation is not exact, the above code is not necessarily equivalent to the summation computation done by this method.
If any stream element is a NaN or the sum is at any point a NaN then the sum will be NaN. The value of a floating-point sum is a function both of the input values as well as the order of addition operations. The order of addition operations of this method is intentionally not defined to allow for implementation flexibility to improve the speed and accuracy of the computed result. In particular, this method may be implemented using compensated summation or other technique to reduce the error bound in the numerical sum compared to a simple summation of double values.
This is a terminal operation.
OptionalDouble min()
Returns an OptionalDouble describing the minimum element of this stream, or an empty OptionalDouble if this stream is empty. The minimum element will be Double.NaN if any stream element was NaN. Unlike the numerical comparison operators, this method considers negative zero to be strictly smaller than positive zero. This is a special case of a reduction and is equivalent to:
return reduce(Double::min);
This is a terminal operation.
OptionalDouble containing the minimum element of this stream, or an empty optional if the stream is emptyOptionalDouble max()
Returns an OptionalDouble describing the maximum element of this stream, or an empty OptionalDouble if this stream is empty. The maximum element will be Double.NaN if any stream element was NaN. Unlike the numerical comparison operators, this method considers negative zero to be strictly smaller than positive zero. This is a special case of a reduction and is equivalent to:
return reduce(Double::max);
This is a terminal operation.
OptionalDouble containing the maximum element of this stream, or an empty optional if the stream is emptylong count()
Returns the count of elements in this stream. This is a special case of a reduction and is equivalent to:
return mapToLong(e -> 1L).sum();
This is a terminal operation.
OptionalDouble average()
Returns an OptionalDouble describing the arithmetic mean of elements of this stream, or an empty optional if this stream is empty. If any recorded value is a NaN or the sum is at any point a NaN then the average will be NaN.
The average returned can vary depending upon the order in which values are recorded. This method may be implemented using compensated summation or other technique to reduce the error bound in the numerical sum used to compute the average.
The average 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 emptyDoubleSummaryStatistics summaryStatistics()
Returns a DoubleSummaryStatistics describing various summary data about the elements of this stream. This is a special case of a reduction.
This is a terminal operation.
DoubleSummaryStatistics describing various summary data about the elements of this streamboolean anyMatch(DoublePredicate 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.
predicate - a non-interfering, stateless predicate to apply to elements of this streamtrue if any elements of the stream match the provided predicate, otherwise false
boolean allMatch(DoublePredicate 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.
true (regardless of P(x)).predicate - a non-interfering, stateless predicate to apply to elements of this streamtrue if either all elements of the stream match the provided predicate or the stream is empty, otherwise false
boolean noneMatch(DoublePredicate 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.
true, regardless of P(x).predicate - a non-interfering, stateless predicate to apply to elements of this streamtrue if either no elements of the stream match the provided predicate or the stream is empty, otherwise false
OptionalDouble findFirst()
Returns an OptionalDouble describing the first element of this stream, or an empty OptionalDouble 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.
OptionalDouble describing the first element of this stream, or an empty OptionalDouble if the stream is emptyOptionalDouble findAny()
Returns an OptionalDouble describing some element of the stream, or an empty OptionalDouble 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.)
OptionalDouble describing some element of this stream, or an empty OptionalDouble if the stream is emptyfindFirst()Stream<Double> boxed()
Returns a Stream consisting of the elements of this stream, boxed to Double.
This is an intermediate operation.
Stream consistent of the elements of this stream, each boxed to a Double
DoubleStream 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.
sequential in interface BaseStream<Double,DoubleStream>
DoubleStream 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.
parallel in interface BaseStream<Double,DoubleStream>
PrimitiveIterator.OfDouble iterator()
Description copied from interface: BaseStream
Returns an iterator for the elements of this stream.
This is a terminal operation.
iterator in interface BaseStream<Double,DoubleStream>
Spliterator.OfDouble spliterator()
Description copied from interface: BaseStream
Returns a spliterator for the elements of this stream.
This is a terminal operation.
spliterator in interface BaseStream<Double,DoubleStream>
static DoubleStream.Builder builder()
Returns a builder for a DoubleStream.
static DoubleStream empty()
Returns an empty sequential DoubleStream.
static DoubleStream of(double t)
Returns a sequential DoubleStream containing a single element.
t - the single elementstatic DoubleStream of(double... values)
Returns a sequential ordered stream whose elements are the specified values.
values - the elements of the new streamstatic DoubleStream iterate(double seed,
DoubleUnaryOperator f) Returns an infinite sequential ordered DoubleStream 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 DoubleStream 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.
seed - the initial elementf - a function to be applied to to the previous element to produce a new elementDoubleStream
static DoubleStream generate(DoubleSupplier s)
Returns an infinite sequential unordered stream where each element is generated by the provided DoubleSupplier. This is suitable for generating constant streams, streams of random elements, etc.
s - the DoubleSupplier for generated elementsDoubleStream
static DoubleStream concat(DoubleStream a,
DoubleStream 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.
StackOverflowException.a - the first streamb - the second stream
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