Back to index...

	/*
	* Copyright (c) 2012, 2020, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/
	package java.util.stream;

	import java.util.Arrays;
	import java.util.DoubleSummaryStatistics;
	import java.util.Objects;
	import java.util.OptionalDouble;
	import java.util.PrimitiveIterator;
	import java.util.Spliterator;
	import java.util.Spliterators;
	import java.util.function.BiConsumer;
	import java.util.function.DoubleBinaryOperator;
	import java.util.function.DoubleConsumer;
	import java.util.function.DoubleFunction;
	import java.util.function.DoublePredicate;
	import java.util.function.DoubleSupplier;
	import java.util.function.DoubleToIntFunction;
	import java.util.function.DoubleToLongFunction;
	import java.util.function.DoubleUnaryOperator;
	import java.util.function.Function;
	import java.util.function.ObjDoubleConsumer;
	import java.util.function.Supplier;

	/**
	* A sequence of primitive double-valued elements supporting sequential and parallel
	* aggregate operations. This is the {@code double} primitive specialization of
	* {@link Stream}.
	*
	* <p>The following example illustrates an aggregate operation using
	* {@link Stream} and {@link DoubleStream}, computing the sum of the weights of the
	* red widgets:
	*
	* <pre>{@code
	* double sum = widgets.stream()
	* .filter(w -> w.getColor() == RED)
	* .mapToDouble(w -> w.getWeight())
	* .sum();
	* }</pre>
	*
	* See the class documentation for {@link Stream} and the package documentation
	* for <a href="package-summary.html">java.util.stream</a> for additional
	* specification of streams, stream operations, stream pipelines, and
	* parallelism.
	*
	* @since 1.8
	* @see Stream
	* @see <a href="package-summary.html">java.util.stream</a>
	*/
	public interface DoubleStream extends BaseStream<Double, DoubleStream> {

	/**
	* Returns a stream consisting of the elements of this stream that match
	* the given predicate.
	*
	* <p>This is an <a href="package-summary.html#StreamOps">intermediate
	* operation</a>.
	*
	* @param predicate a <a href="package-summary.html#NonInterference">non-interfering</a>,
	* <a href="package-summary.html#Statelessness">stateless</a>
	* predicate to apply to each element to determine if it
	* should be included
	* @return the new stream
	*/
	DoubleStream filter(DoublePredicate predicate);

	/**
	* Returns a stream consisting of the results of applying the given
	* function to the elements of this stream.
	*
	* <p>This is an <a href="package-summary.html#StreamOps">intermediate
	* operation</a>.
	*
	* @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>,
	* <a href="package-summary.html#Statelessness">stateless</a>
	* function to apply to each element
	* @return the new stream
	*/
	DoubleStream map(DoubleUnaryOperator mapper);

	/**
	* Returns an object-valued {@code Stream} consisting of the results of
	* applying the given function to the elements of this stream.
	*
	* <p>This is an <a href="package-summary.html#StreamOps">
	* intermediate operation</a>.
	*
	* @param <U> the element type of the new stream
	* @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>,
	* <a href="package-summary.html#Statelessness">stateless</a>
	* function to apply to each element
	* @return the new stream
	*/
	<U> Stream<U> mapToObj(DoubleFunction<? extends U> mapper);

	/**
	* Returns an {@code IntStream} consisting of the results of applying the
	* given function to the elements of this stream.
	*
	* <p>This is an <a href="package-summary.html#StreamOps">intermediate
	* operation</a>.
	*
	* @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>,
	* <a href="package-summary.html#Statelessness">stateless</a>
	* function to apply to each element
	* @return the new stream
	*/
	IntStream mapToInt(DoubleToIntFunction mapper);

	/**
	* Returns a {@code LongStream} consisting of the results of applying the
	* given function to the elements of this stream.
	*
	* <p>This is an <a href="package-summary.html#StreamOps">intermediate
	* operation</a>.
	*
	* @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>,
	* <a href="package-summary.html#Statelessness">stateless</a>
	* function to apply to each element
	* @return the new stream
	*/
	LongStream mapToLong(DoubleToLongFunction 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
	* {@link java.util.stream.BaseStream#close() closed} after its contents
	* have been placed into this stream. (If a mapped stream is {@code null}
	* an empty stream is used, instead.)
	*
	* <p>This is an <a href="package-summary.html#StreamOps">intermediate
	* operation</a>.
	*
	* @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>,
	* <a href="package-summary.html#Statelessness">stateless</a>
	* function to apply to each element which produces a
	* {@code DoubleStream} of new values
	* @return the new stream
	* @see Stream#flatMap(Function)
	*/
	DoubleStream flatMap(DoubleFunction<? extends DoubleStream> mapper);

	/**
	* 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 {@linkplain DoubleConsumer consumer} argument
	* that accepts replacement elements. The mapping function calls the consumer
	* zero or more times to provide the replacement elements.
	*
	* <p>This is an <a href="package-summary.html#StreamOps">intermediate
	* operation</a>.
	*
	* <p>If the {@linkplain DoubleConsumer consumer} argument is used outside the scope of
	* its application to the mapping function, the results are undefined.
	*
	* @implSpec
	* The default implementation invokes {@link #flatMap flatMap} on this stream,
	* passing a function that behaves as follows. First, it calls the mapper function
	* with a {@code DoubleConsumer} that accumulates replacement elements into a newly created
	* internal buffer. When the mapper function returns, it creates a {@code DoubleStream} from the
	* internal buffer. Finally, it returns this stream to {@code flatMap}.
	*
	* @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>,
	* <a href="package-summary.html#Statelessness">stateless</a>
	* function that generates replacement elements
	* @return the new stream
	* @see Stream#mapMulti Stream.mapMulti
	* @since 16
	*/
	default DoubleStream mapMulti(DoubleMapMultiConsumer mapper) {
	Objects.requireNonNull(mapper);
	return flatMap(e -> {
	SpinedBuffer.OfDouble buffer = new SpinedBuffer.OfDouble();
	mapper.accept(e, buffer);
	return StreamSupport.doubleStream(buffer.spliterator(), false);
	});
	}

	/**
	* Returns a stream consisting of the distinct elements of this stream. The
	* elements are compared for equality according to
	* {@link java.lang.Double#compare(double, double)}.
	*
	* <p>This is a <a href="package-summary.html#StreamOps">stateful
	* intermediate operation</a>.
	*
	* @return the result stream
	*/
	DoubleStream distinct();

	/**
	* Returns a stream consisting of the elements of this stream in sorted
	* order. The elements are compared for equality according to
	* {@link java.lang.Double#compare(double, double)}.
	*
	* <p>This is a <a href="package-summary.html#StreamOps">stateful
	* intermediate operation</a>.
	*
	* @return the result stream
	*/
	DoubleStream sorted();

	/**
	* 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.
	*
	* <p>This is an <a href="package-summary.html#StreamOps">intermediate
	* operation</a>.
	*
	* <p>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.
	*
	* @apiNote This method exists mainly to support debugging, where you want
	* to see the elements as they flow past a certain point in a pipeline:
	* <pre>{@code
	* 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();
	* }</pre>
	*
	* <p>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 {@code findFirst}, or in the example described in
	* {@link #count}), the action will not be invoked for those elements.
	*
	* @param action a <a href="package-summary.html#NonInterference">
	* non-interfering</a> action to perform on the elements as
	* they are consumed from the stream
	* @return the new stream
	*/
	DoubleStream peek(DoubleConsumer action);

	/**
	* Returns a stream consisting of the elements of this stream, truncated
	* to be no longer than {@code maxSize} in length.
	*
	* <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
	* stateful intermediate operation</a>.
	*
	* @apiNote
	* While {@code limit()} is generally a cheap operation on sequential
	* stream pipelines, it can be quite expensive on ordered parallel pipelines,
	* especially for large values of {@code maxSize}, since {@code limit(n)}
	* is constrained to return not just any <em>n</em> elements, but the
	* <em>first n</em> elements in the encounter order. Using an unordered
	* stream source (such as {@link #generate(DoubleSupplier)}) or removing the
	* ordering constraint with {@link #unordered()} may result in significant
	* speedups of {@code 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
	* {@code limit()} in parallel pipelines, switching to sequential execution
	* with {@link #sequential()} may improve performance.
	*
	* @param maxSize the number of elements the stream should be limited to
	* @return the new stream
	* @throws IllegalArgumentException if {@code maxSize} is negative
	*/
	DoubleStream limit(long maxSize);

	/**
	* Returns a stream consisting of the remaining elements of this stream
	* after discarding the first {@code n} elements of the stream.
	* If this stream contains fewer than {@code n} elements then an
	* empty stream will be returned.
	*
	* <p>This is a <a href="package-summary.html#StreamOps">stateful
	* intermediate operation</a>.
	*
	* @apiNote
	* While {@code skip()} is generally a cheap operation on sequential
	* stream pipelines, it can be quite expensive on ordered parallel pipelines,
	* especially for large values of {@code n}, since {@code skip(n)}
	* is constrained to skip not just any <em>n</em> elements, but the
	* <em>first n</em> elements in the encounter order. Using an unordered
	* stream source (such as {@link #generate(DoubleSupplier)}) or removing the
	* ordering constraint with {@link #unordered()} may result in significant
	* speedups of {@code 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
	* {@code skip()} in parallel pipelines, switching to sequential execution
	* with {@link #sequential()} may improve performance.
	*
	* @param n the number of leading elements to skip
	* @return the new stream
	* @throws IllegalArgumentException if {@code n} is negative
	*/
	DoubleStream skip(long n);

	/**
	* 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.
	*
	* <p>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.
	*
	* <p>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).
	*
	* <p>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).
	*
	* <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
	* stateful intermediate operation</a>.
	*
	* @implSpec
	* The default implementation obtains the {@link #spliterator() 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 {@link #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.
	*
	* @apiNote
	* While {@code 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
	* {@link #generate(DoubleSupplier)}) or removing the ordering constraint
	* with {@link #unordered()} may result in significant speedups of
	* {@code 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
	* {@code takeWhile()} in parallel pipelines, switching to sequential
	* execution with {@link #sequential()} may improve performance.
	*
	* @param predicate a <a href="package-summary.html#NonInterference">non-interfering</a>,
	* <a href="package-summary.html#Statelessness">stateless</a>
	* predicate to apply to elements to determine the longest
	* prefix of elements.
	* @return the new stream
	* @since 9
	*/
	default DoubleStream takeWhile(DoublePredicate predicate) {
	Objects.requireNonNull(predicate);
	// Reuses the unordered spliterator, which, when encounter is present,
	// is safe to use as long as it configured not to split
	return StreamSupport.doubleStream(
	new WhileOps.UnorderedWhileSpliterator.OfDouble.Taking(spliterator(), true, predicate),
	isParallel()).onClose(this::close);
	}

	/**
	* 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.
	*
	* <p>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.
	*
	* <p>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).
	*
	* <p>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).
	*
	* <p>This is a <a href="package-summary.html#StreamOps">stateful
	* intermediate operation</a>.
	*
	* @implSpec
	* The default implementation obtains the {@link #spliterator() 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 {@link #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.
	*
	* @apiNote
	* While {@code 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
	* {@link #generate(DoubleSupplier)}) or removing the ordering constraint
	* with {@link #unordered()} may result in significant speedups of
	* {@code 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
	* {@code dropWhile()} in parallel pipelines, switching to sequential
	* execution with {@link #sequential()} may improve performance.
	*
	* @param predicate a <a href="package-summary.html#NonInterference">non-interfering</a>,
	* <a href="package-summary.html#Statelessness">stateless</a>
	* predicate to apply to elements to determine the longest
	* prefix of elements.
	* @return the new stream
	* @since 9
	*/
	default DoubleStream dropWhile(DoublePredicate predicate) {
	Objects.requireNonNull(predicate);
	// Reuses the unordered spliterator, which, when encounter is present,
	// is safe to use as long as it configured not to split
	return StreamSupport.doubleStream(
	new WhileOps.UnorderedWhileSpliterator.OfDouble.Dropping(spliterator(), true, predicate),
	isParallel()).onClose(this::close);
	}

	/**
	* Performs an action for each element of this stream.
	*
	* <p>This is a <a href="package-summary.html#StreamOps">terminal
	* operation</a>.
	*
	* <p>For parallel stream pipelines, this operation does <em>not</em>
	* 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.
	*
	* @param action a <a href="package-summary.html#NonInterference">
	* non-interfering</a> action to perform on the elements
	*/
	void forEach(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.
	*
	* <p>This is a <a href="package-summary.html#StreamOps">terminal
	* operation</a>.
	*
	* @param action a <a href="package-summary.html#NonInterference">
	* non-interfering</a> action to perform on the elements
	* @see #forEach(DoubleConsumer)
	*/
	void forEachOrdered(DoubleConsumer action);

	/**
	* Returns an array containing the elements of this stream.
	*
	* <p>This is a <a href="package-summary.html#StreamOps">terminal
	* operation</a>.
	*
	* @return an array containing the elements of this stream
	*/
	double[] toArray();

	/**
	* Performs a <a href="package-summary.html#Reduction">reduction</a> on the
	* elements of this stream, using the provided identity value and an
	* <a href="package-summary.html#Associativity">associative</a>
	* accumulation function, and returns the reduced value. This is equivalent
	* to:
	* <pre>{@code
	* double result = identity;
	* for (double element : this stream)
	* result = accumulator.applyAsDouble(result, element)
	* return result;
	* }</pre>
	*
	* but is not constrained to execute sequentially.
	*
	* <p>The {@code identity} value must be an identity for the accumulator
	* function. This means that for all {@code x},
	* {@code accumulator.apply(identity, x)} is equal to {@code x}.
	* The {@code accumulator} function must be an
	* <a href="package-summary.html#Associativity">associative</a> function.
	*
	* <p>This is a <a href="package-summary.html#StreamOps">terminal
	* operation</a>.
	*
	* @apiNote Sum, min, max, and average are all special cases of reduction.
	* Summing a stream of numbers can be expressed as:
	*
	* <pre>{@code
	* double sum = numbers.reduce(0, (a, b) -> a+b);
	* }</pre>
	*
	* or more compactly:
	*
	* <pre>{@code
	* double sum = numbers.reduce(0, Double::sum);
	* }</pre>
	*
	* <p>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.
	*
	* @param identity the identity value for the accumulating function
	* @param op an <a href="package-summary.html#Associativity">associative</a>,
	* <a href="package-summary.html#NonInterference">non-interfering</a>,
	* <a href="package-summary.html#Statelessness">stateless</a>
	* function for combining two values
	* @return the result of the reduction
	* @see #sum()
	* @see #min()
	* @see #max()
	* @see #average()
	*/
	double reduce(double identity, DoubleBinaryOperator op);

	/**
	* Performs a <a href="package-summary.html#Reduction">reduction</a> on the
	* elements of this stream, using an
	* <a href="package-summary.html#Associativity">associative</a> accumulation
	* function, and returns an {@code OptionalDouble} describing the reduced
	* value, if any. This is equivalent to:
	* <pre>{@code
	* 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();
	* }</pre>
	*
	* but is not constrained to execute sequentially.
	*
	* <p>The {@code accumulator} function must be an
	* <a href="package-summary.html#Associativity">associative</a> function.
	*
	* <p>This is a <a href="package-summary.html#StreamOps">terminal
	* operation</a>.
	*
	* @param op an <a href="package-summary.html#Associativity">associative</a>,
	* <a href="package-summary.html#NonInterference">non-interfering</a>,
	* <a href="package-summary.html#Statelessness">stateless</a>
	* function for combining two values
	* @return the result of the reduction
	* @see #reduce(double, DoubleBinaryOperator)
	*/
	OptionalDouble reduce(DoubleBinaryOperator op);

	/**
	* Performs a <a href="package-summary.html#MutableReduction">mutable
	* reduction</a> 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 {@code ArrayList}, and elements are incorporated by updating
	* the state of the result rather than by replacing the result. This
	* produces a result equivalent to:
	* <pre>{@code
	* R result = supplier.get();
	* for (double element : this stream)
	* accumulator.accept(result, element);
	* return result;
	* }</pre>
	*
	* <p>Like {@link #reduce(double, DoubleBinaryOperator)}, {@code collect}
	* operations can be parallelized without requiring additional
	* synchronization.
	*
	* <p>This is a <a href="package-summary.html#StreamOps">terminal
	* operation</a>.
	*
	* @param <R> the type of the mutable result container
	* @param 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.
	* @param accumulator an <a href="package-summary.html#Associativity">associative</a>,
	* <a href="package-summary.html#NonInterference">non-interfering</a>,
	* <a href="package-summary.html#Statelessness">stateless</a>
	* function that must fold an element into a result
	* container.
	* @param combiner an <a href="package-summary.html#Associativity">associative</a>,
	* <a href="package-summary.html#NonInterference">non-interfering</a>,
	* <a href="package-summary.html#Statelessness">stateless</a>
	* 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.
	* @return the result of the reduction
	* @see Stream#collect(Supplier, BiConsumer, BiConsumer)
	*/
	<R> R collect(Supplier<R> supplier,
	ObjDoubleConsumer<R> accumulator,
	BiConsumer<R, R> combiner);

	/**
	* Returns the sum of elements in this stream.
	*
	* Summation is a special case of a <a
	* href="package-summary.html#Reduction">reduction</a>. If
	* floating-point summation were exact, this method would be
	* equivalent to:
	*
	* <pre>{@code
	* return reduce(0, Double::sum);
	* }</pre>
	*
	* However, since floating-point summation is not exact, the above
	* code is not necessarily equivalent to the summation computation
	* done by this method.
	*
	* <p>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 {@code double}
	* values.
	*
	* Because of the unspecified order of operations and the
	* possibility of using differing summation schemes, the output of
	* this method may vary on the same input elements.
	*
	* <p>Various conditions can result in a non-finite sum being
	* computed. This can occur even if the all the elements
	* being summed are finite. If any element is non-finite,
	* the sum will be non-finite:
	*
	* <ul>
	*
	* <li>If any element is a NaN, then the final sum will be
	* NaN.
	*
	* <li>If the elements contain one or more infinities, the
	* sum will be infinite or NaN.
	*
	* <ul>
	*
	* <li>If the elements contain infinities of opposite sign,
	* the sum will be NaN.
	*
	* <li>If the elements contain infinities of one sign and
	* an intermediate sum overflows to an infinity of the opposite
	* sign, the sum may be NaN.
	*
	* </ul>
	*
	* </ul>
	*
	* It is possible for intermediate sums of finite values to
	* overflow into opposite-signed infinities; if that occurs, the
	* final sum will be NaN even if the elements are all
	* finite.
	*
	* If all the elements are zero, the sign of zero is
	* <em>not</em> guaranteed to be preserved in the final sum.
	*
	* <p>This is a <a href="package-summary.html#StreamOps">terminal
	* operation</a>.
	*
	* @apiNote Elements sorted by increasing absolute magnitude tend
	* to yield more accurate results.
	*
	* @return the sum of elements in this stream
	*/
	double sum();

	/**
	* Returns an {@code OptionalDouble} describing the minimum element of this
	* stream, or an empty OptionalDouble if this stream is empty. The minimum
	* element will be {@code 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
	* <a href="package-summary.html#Reduction">reduction</a> and is
	* equivalent to:
	* <pre>{@code
	* return reduce(Double::min);
	* }</pre>
	*
	* <p>This is a <a href="package-summary.html#StreamOps">terminal
	* operation</a>.
	*
	* @return an {@code OptionalDouble} containing the minimum element of this
	* stream, or an empty optional if the stream is empty
	*/
	OptionalDouble min();

	/**
	* Returns an {@code OptionalDouble} describing the maximum element of this
	* stream, or an empty OptionalDouble if this stream is empty. The maximum
	* element will be {@code 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
	* <a href="package-summary.html#Reduction">reduction</a> and is
	* equivalent to:
	* <pre>{@code
	* return reduce(Double::max);
	* }</pre>
	*
	* <p>This is a <a href="package-summary.html#StreamOps">terminal
	* operation</a>.
	*
	* @return an {@code OptionalDouble} containing the maximum element of this
	* stream, or an empty optional if the stream is empty
	*/
	OptionalDouble max();

	/**
	* Returns the count of elements in this stream. This is a special case of
	* a <a href="package-summary.html#Reduction">reduction</a> and is
	* equivalent to:
	* <pre>{@code
	* return mapToLong(e -> 1L).sum();
	* }</pre>
	*
	* <p>This is a <a href="package-summary.html#StreamOps">terminal operation</a>.
	*
	* @apiNote
	* An implementation may choose to not execute the stream pipeline (either
	* sequentially or in parallel) if it is capable of computing the count
	* directly from the stream source. In such cases no source elements will
	* be traversed and no intermediate operations will be evaluated.
	* Behavioral parameters with side-effects, which are strongly discouraged
	* except for harmless cases such as debugging, may be affected. For
	* example, consider the following stream:
	* <pre>{@code
	* DoubleStream s = DoubleStream.of(1, 2, 3, 4);
	* long count = s.peek(System.out::println).count();
	* }</pre>
	* The number of elements covered by the stream source is known and the
	* intermediate operation, {@code peek}, does not inject into or remove
	* elements from the stream (as may be the case for {@code flatMap} or
	* {@code 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.
	*
	* @return the count of elements in this stream
	*/
	long count();

	/**
	* Returns an {@code OptionalDouble} describing the arithmetic
	* mean of elements of this stream, or an empty optional if this
	* stream is empty.
	*
	* <p>The computed average can vary numerically and have the
	* special case behavior as computing the sum; see {@link #sum}
	* for details.
	*
	* <p>The average is a special case of a <a
	* href="package-summary.html#Reduction">reduction</a>.
	*
	* <p>This is a <a href="package-summary.html#StreamOps">terminal
	* operation</a>.
	*
	* @apiNote Elements sorted by increasing absolute magnitude tend
	* to yield more accurate results.
	*
	* @return an {@code OptionalDouble} containing the average element of this
	* stream, or an empty optional if the stream is empty
	*/
	OptionalDouble average();

	/**
	* Returns a {@code DoubleSummaryStatistics} describing various summary data
	* about the elements of this stream. This is a special
	* case of a <a href="package-summary.html#Reduction">reduction</a>.
	*
	* <p>This is a <a href="package-summary.html#StreamOps">terminal
	* operation</a>.
	*
	* @return a {@code DoubleSummaryStatistics} describing various summary data
	* about the elements of this stream
	*/
	DoubleSummaryStatistics summaryStatistics();

	/**
	* 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
	* {@code false} is returned and the predicate is not evaluated.
	*
	* <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
	* terminal operation</a>.
	*
	* @apiNote
	* This method evaluates the <em>existential quantification</em> of the
	* predicate over the elements of the stream (for some x P(x)).
	*
	* @param predicate a <a href="package-summary.html#NonInterference">non-interfering</a>,
	* <a href="package-summary.html#Statelessness">stateless</a>
	* predicate to apply to elements of this stream
	* @return {@code true} if any elements of the stream match the provided
	* predicate, otherwise {@code false}
	*/
	boolean anyMatch(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 {@code true} is
	* returned and the predicate is not evaluated.
	*
	* <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
	* terminal operation</a>.
	*
	* @apiNote
	* This method evaluates the <em>universal quantification</em> 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 <em>vacuously
	* satisfied</em> and is always {@code true} (regardless of P(x)).
	*
	* @param predicate a <a href="package-summary.html#NonInterference">non-interfering</a>,
	* <a href="package-summary.html#Statelessness">stateless</a>
	* predicate to apply to elements of this stream
	* @return {@code true} if either all elements of the stream match the
	* provided predicate or the stream is empty, otherwise {@code false}
	*/
	boolean allMatch(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 {@code true} is
	* returned and the predicate is not evaluated.
	*
	* <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
	* terminal operation</a>.
	*
	* @apiNote
	* This method evaluates the <em>universal quantification</em> 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 {@code true}, regardless of P(x).
	*
	* @param predicate a <a href="package-summary.html#NonInterference">non-interfering</a>,
	* <a href="package-summary.html#Statelessness">stateless</a>
	* predicate to apply to elements of this stream
	* @return {@code true} if either no elements of the stream match the
	* provided predicate or the stream is empty, otherwise {@code false}
	*/
	boolean noneMatch(DoublePredicate predicate);

	/**
	* Returns an {@link OptionalDouble} describing the first element of this
	* stream, or an empty {@code OptionalDouble} if the stream is empty. If
	* the stream has no encounter order, then any element may be returned.
	*
	* <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
	* terminal operation</a>.
	*
	* @return an {@code OptionalDouble} describing the first element of this
	* stream, or an empty {@code OptionalDouble} if the stream is empty
	*/
	OptionalDouble findFirst();

	/**
	* Returns an {@link OptionalDouble} describing some element of the stream,
	* or an empty {@code OptionalDouble} if the stream is empty.
	*
	* <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
	* terminal operation</a>.
	*
	* <p>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 {@link #findFirst()} instead.)
	*
	* @return an {@code OptionalDouble} describing some element of this stream,
	* or an empty {@code OptionalDouble} if the stream is empty
	* @see #findFirst()
	*/
	OptionalDouble findAny();

	/**
	* Returns a {@code Stream} consisting of the elements of this stream,
	* boxed to {@code Double}.
	*
	* <p>This is an <a href="package-summary.html#StreamOps">intermediate
	* operation</a>.
	*
	* @return a {@code Stream} consistent of the elements of this stream,
	* each boxed to a {@code Double}
	*/
	Stream<Double> boxed();

	@Override
	DoubleStream sequential();

	@Override
	DoubleStream parallel();

	@Override
	PrimitiveIterator.OfDouble iterator();

	@Override
	Spliterator.OfDouble spliterator();


	// Static factories

	/**
	* Returns a builder for a {@code DoubleStream}.
	*
	* @return a stream builder
	*/
	public static Builder builder() {
	return new Streams.DoubleStreamBuilderImpl();
	}

	/**
	* Returns an empty sequential {@code DoubleStream}.
	*
	* @return an empty sequential stream
	*/
	public static DoubleStream empty() {
	return StreamSupport.doubleStream(Spliterators.emptyDoubleSpliterator(), false);
	}

	/**
	* Returns a sequential {@code DoubleStream} containing a single element.
	*
	* @param t the single element
	* @return a singleton sequential stream
	*/
	public static DoubleStream of(double t) {
	return StreamSupport.doubleStream(new Streams.DoubleStreamBuilderImpl(t), false);
	}

	/**
	* Returns a sequential ordered stream whose elements are the specified values.
	*
	* @param values the elements of the new stream
	* @return the new stream
	*/
	public static DoubleStream of(double... values) {
	return Arrays.stream(values);
	}

	/**
	* Returns an infinite sequential ordered {@code DoubleStream} produced by iterative
	* application of a function {@code f} to an initial element {@code seed},
	* producing a {@code Stream} consisting of {@code seed}, {@code f(seed)},
	* {@code f(f(seed))}, etc.
	*
	* <p>The first element (position {@code 0}) in the {@code DoubleStream}
	* will be the provided {@code seed}. For {@code n > 0}, the element at
	* position {@code n}, will be the result of applying the function {@code f}
	* to the element at position {@code n - 1}.
	*
	* <p>The action of applying {@code f} for one element
	* <a href="../concurrent/package-summary.html#MemoryVisibility"><i>happens-before</i></a>
	* the action of applying {@code f} for subsequent elements. For any given
	* element the action may be performed in whatever thread the library
	* chooses.
	*
	* @param seed the initial element
	* @param f a function to be applied to the previous element to produce
	* a new element
	* @return a new sequential {@code DoubleStream}
	*/
	public static DoubleStream iterate(final double seed, final DoubleUnaryOperator f) {
	Objects.requireNonNull(f);
	Spliterator.OfDouble spliterator = new Spliterators.AbstractDoubleSpliterator(Long.MAX_VALUE,
	Spliterator.ORDERED \| Spliterator.IMMUTABLE \| Spliterator.NONNULL) {
	double prev;
	boolean started;

	@Override
	public boolean tryAdvance(DoubleConsumer action) {
	Objects.requireNonNull(action);
	double t;
	if (started)
	t = f.applyAsDouble(prev);
	else {
	t = seed;
	started = true;
	}
	action.accept(prev = t);
	return true;
	}
	};
	return StreamSupport.doubleStream(spliterator, false);
	}

	/**
	* Returns a sequential ordered {@code DoubleStream} produced by iterative
	* application of the given {@code next} function to an initial element,
	* conditioned on satisfying the given {@code hasNext} predicate. The
	* stream terminates as soon as the {@code hasNext} predicate returns false.
	*
	* <p>{@code DoubleStream.iterate} should produce the same sequence of elements as
	* produced by the corresponding for-loop:
	* <pre>{@code
	* for (double index=seed; hasNext.test(index); index = next.applyAsDouble(index)) {
	* ...
	* }
	* }</pre>
	*
	* <p>The resulting sequence may be empty if the {@code hasNext} predicate
	* does not hold on the seed value. Otherwise the first element will be the
	* supplied {@code seed} value, the next element (if present) will be the
	* result of applying the {@code next} function to the {@code seed} value,
	* and so on iteratively until the {@code hasNext} predicate indicates that
	* the stream should terminate.
	*
	* <p>The action of applying the {@code hasNext} predicate to an element
	* <a href="../concurrent/package-summary.html#MemoryVisibility"><i>happens-before</i></a>
	* the action of applying the {@code next} function to that element. The
	* action of applying the {@code next} function for one element
	* <i>happens-before</i> the action of applying the {@code hasNext}
	* predicate for subsequent elements. For any given element an action may
	* be performed in whatever thread the library chooses.
	*
	* @param seed the initial element
	* @param hasNext a predicate to apply to elements to determine when the
	* stream must terminate.
	* @param next a function to be applied to the previous element to produce
	* a new element
	* @return a new sequential {@code DoubleStream}
	* @since 9
	*/
	public static DoubleStream iterate(double seed, DoublePredicate hasNext, DoubleUnaryOperator next) {
	Objects.requireNonNull(next);
	Objects.requireNonNull(hasNext);
	Spliterator.OfDouble spliterator = new Spliterators.AbstractDoubleSpliterator(Long.MAX_VALUE,
	Spliterator.ORDERED \| Spliterator.IMMUTABLE \| Spliterator.NONNULL) {
	double prev;
	boolean started, finished;

	@Override
	public boolean tryAdvance(DoubleConsumer action) {
	Objects.requireNonNull(action);
	if (finished)
	return false;
	double t;
	if (started)
	t = next.applyAsDouble(prev);
	else {
	t = seed;
	started = true;
	}
	if (!hasNext.test(t)) {
	finished = true;
	return false;
	}
	action.accept(prev = t);
	return true;
	}

	@Override
	public void forEachRemaining(DoubleConsumer action) {
	Objects.requireNonNull(action);
	if (finished)
	return;
	finished = true;
	double t = started ? next.applyAsDouble(prev) : seed;
	while (hasNext.test(t)) {
	action.accept(t);
	t = next.applyAsDouble(t);
	}
	}
	};
	return StreamSupport.doubleStream(spliterator, false);
	}

	/**
	* Returns an infinite sequential unordered stream where each element is
	* generated by the provided {@code DoubleSupplier}. This is suitable for
	* generating constant streams, streams of random elements, etc.
	*
	* @param s the {@code DoubleSupplier} for generated elements
	* @return a new infinite sequential unordered {@code DoubleStream}
	*/
	public static DoubleStream generate(DoubleSupplier s) {
	Objects.requireNonNull(s);
	return StreamSupport.doubleStream(
	new StreamSpliterators.InfiniteSupplyingSpliterator.OfDouble(Long.MAX_VALUE, s), false);
	}

	/**
	* 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.
	*
	* <p>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.
	*
	* @implNote
	* Use caution when constructing streams from repeated concatenation.
	* Accessing an element of a deeply concatenated stream can result in deep
	* call chains, or even {@code StackOverflowError}.
	*
	* @apiNote
	* To preserve optimization opportunities this method binds each stream to
	* its source and accepts only two streams as parameters. For example, the
	* exact size of the concatenated stream source can be computed if the exact
	* size of each input stream source is known.
	* To concatenate more streams without binding, or without nested calls to
	* this method, try creating a stream of streams and flat-mapping with the
	* identity function, for example:
	* <pre>{@code
	* DoubleStream concat = Stream.of(s1, s2, s3, s4).flatMapToDouble(s -> s);
	* }</pre>
	*
	* @param a the first stream
	* @param b the second stream
	* @return the concatenation of the two input streams
	*/
	public static DoubleStream concat(DoubleStream a, DoubleStream b) {
	Objects.requireNonNull(a);
	Objects.requireNonNull(b);

	Spliterator.OfDouble split = new Streams.ConcatSpliterator.OfDouble(
	a.spliterator(), b.spliterator());
	DoubleStream stream = StreamSupport.doubleStream(split, a.isParallel() \|\| b.isParallel());
	return stream.onClose(Streams.composedClose(a, b));
	}

	/**
	* A mutable builder for a {@code DoubleStream}.
	*
	* <p>A stream builder has a lifecycle, which starts in a building
	* phase, during which elements can be added, and then transitions to a built
	* phase, after which elements may not be added. The built phase
	* begins when the {@link #build()} method is called, which creates an
	* ordered stream whose elements are the elements that were added to the
	* stream builder, in the order they were added.
	*
	* @see DoubleStream#builder()
	* @since 1.8
	*/
	public interface Builder extends DoubleConsumer {

	/**
	* Adds an element to the stream being built.
	*
	* @throws IllegalStateException if the builder has already transitioned
	* to the built state
	*/
	@Override
	void accept(double t);

	/**
	* Adds an element to the stream being built.
	*
	* @implSpec
	* The default implementation behaves as if:
	* <pre>{@code
	* accept(t)
	* return this;
	* }</pre>
	*
	* @param t the element to add
	* @return {@code this} builder
	* @throws IllegalStateException if the builder has already transitioned
	* to the built state
	*/
	default Builder add(double t) {
	accept(t);
	return this;
	}

	/**
	* Builds the stream, transitioning this builder to the built state.
	* An {@code IllegalStateException} is thrown if there are further
	* attempts to operate on the builder after it has entered the built
	* state.
	*
	* @return the built stream
	* @throws IllegalStateException if the builder has already transitioned
	* to the built state
	*/
	DoubleStream build();
	}

	/**
	* Represents an operation that accepts a {@code double}-valued argument
	* and a DoubleConsumer, and returns no result. This functional interface is
	* used by {@link DoubleStream#mapMulti(DoubleMapMultiConsumer) DoubleStream.mapMulti}
	* to replace a double value with zero or more double values.
	*
	* <p>This is a <a href="../function/package-summary.html">functional interface</a>
	* whose functional method is {@link #accept(double, DoubleConsumer)}.
	*
	* @see DoubleStream#mapMulti(DoubleMapMultiConsumer)
	*
	* @since 16
	*/
	@FunctionalInterface
	interface DoubleMapMultiConsumer {

	/**
	* Replaces the given {@code value} with zero or more values by feeding the mapped
	* values to the {@code dc} consumer.
	*
	* @param value the double value coming from upstream
	* @param dc a {@code DoubleConsumer} accepting the mapped values
	*/
	void accept(double value, DoubleConsumer dc);
	}
	}

Back to index...