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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * 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
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 * 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,
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 *
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package java.util.stream;

import java.util.DoubleSummaryStatistics;
import java.util.OptionalDouble;
import java.util.PrimitiveIterator;
import java.util.Spliterator;
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.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 elements supporting sequential and parallel
 * bulk operations. Streams support lazy intermediate operations (transforming
 * a stream to another stream) such as {@code filter} and {@code map}, and terminal
 * operations (consuming the contents of a stream to produce a result or
 * side-effect), such as {@code forEach}, {@code findFirst}, and {@code
 * iterator}.  Once an operation has been performed on a stream, it
 * is considered <em>consumed</em> and no longer usable for other operations.
 *
 * <p>For sequential stream pipelines, all operations are performed in the
 * <a href="package-summary.html#Ordering">encounter order</a> of the pipeline
 * source, if the pipeline source has a defined encounter order.
 *
 * <p>For parallel stream pipelines, unless otherwise specified, intermediate
 * stream operations preserve the <a href="package-summary.html#Ordering">
 * encounter order</a> of their source, and terminal operations
 * respect the encounter order of their source, if the source
 * has an encounter order.  Provided that and parameters to stream operations
 * satisfy the <a href="package-summary.html#NonInterference">non-interference
 * requirements</a>, and excepting differences arising from the absence of
 * a defined encounter order, the result of a stream pipeline should be the
 * stable across multiple executions of the same operations on the same source.
 * However, the timing and thread in which side-effects occur (for those
 * operations which are allowed to produce side-effects, such as
 * {@link #forEach(DoubleConsumer)}), are explicitly nondeterministic for parallel
 * execution of stream pipelines.
 *
 * <p>Unless otherwise noted, passing a {@code null} argument to any stream
 * method may result in a {@link NullPointerException}.
 *
 * @apiNote
 * Streams are not data structures; they do not manage the storage for their
 * elements, nor do they support access to individual elements.  However,
 * you can use the {@link #iterator()} or {@link #spliterator()} operations to
 * perform a controlled traversal.
 *
 * @since 1.8
 * @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, 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, 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, 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, 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, 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 the stream produced by applying the
     * provided mapping function to each element.
     *
     * <p>This is an <a href="package-summary.html#StreamOps">intermediate
     * operation</a>.
     *
     * @apiNote
     * The {@code flatMap()} operation has the effect of applying a one-to-many
     * tranformation to the elements of the stream, and then flattening the
     * resulting elements into a new stream. For example, if {@code orders}
     * is a stream of purchase orders, and each purchase order contains a
     * collection of line items, then the following produces a stream of line
     * items:
     * <pre>{@code
     *     orderStream.flatMap(order -> order.getLineItems().stream())...
     * }</pre>
     *
     * @param mapper a <a href="package-summary.html#NonInterference">
     *               non-interfering, stateless</a> function to apply to
     *               each element which produces an {@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 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
     *     list.stream()
     *         .filter(filteringFunction)
     *         .peek(e -> {System.out.println("Filtered value: " + e); });
     *         .map(mappingFunction)
     *         .peek(e -> {System.out.println("Mapped value: " + e); });
     *         .collect(Collectors.toDoubleSummaryStastistics());
     * }</pre>
     *
     * @param consumer 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 consumer);

    /**
     * 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>.
     *
     * @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 indexing {@code startInclusive} elements into the stream. If the
     * {@code startInclusive} index lies past the end of this stream then an
     * empty stream will be returned.
     *
     * <p>This is a <a href="package-summary.html#StreamOps">stateful
     * intermediate operation</a>.
     *
     * @param startInclusive the number of leading elements to skip
     * @return the new stream
     * @throws IllegalArgumentException if {@code startInclusive} is negative
     */
    DoubleStream substream(long startInclusive);

    /**
     * Returns a stream consisting of the remaining elements of this stream
     * after indexing {@code startInclusive} elements into the stream and
     * truncated to contain no more than {@code endExclusive - startInclusive}
     * elements. If the {@code startInclusive} index lies past the end
     * of this stream then an empty stream will be returned.
     *
     * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
     * stateful intermediate operation</a>.
     *
     * @param startInclusive the starting position of the substream, inclusive
     * @param endExclusive the ending position of the substream, exclusive
     * @return the new stream
     * @throws IllegalArgumentException if {@code startInclusive} or
     * {@code endExclusive} is negative or {@code startInclusive} is greater
     * than {@code endExclusive}
     */
    DoubleStream substream(long startInclusive, long endExclusive);

    /**
     * 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.apply(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,
     *                    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.apply(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,
     *           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 value holder,
     * 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 = resultFactory.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> type of the result
     * @param resultFactory 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.
     * @param accumulator an <a href="package-summary.html#Associativity">associative</a>
     *                    <a href="package-summary.html#NonInterference">non-interfering,
     *                    stateless</a> function for incorporating an additional
     *                    element into a result
     * @param combiner an <a href="package-summary.html#Associativity">associative</a>
     *                 <a href="package-summary.html#NonInterference">non-interfering,
     *                 stateless</a> function for combining two values, which
     *                 must be compatible with the accumulator function
     * @return the result of the reduction
     * @see Stream#collect(Supplier, BiConsumer, BiConsumer)
     */
    <R> R collect(Supplier<R> resultFactory,
                  ObjDoubleConsumer<R> accumulator,
                  BiConsumer<R, R> combiner);

    /**
     * Returns the sum of elements in this stream.  The sum returned can vary
     * depending upon the order in which elements are encountered.  This is due
     * to accumulated rounding error in addition of values of differing
     * magnitudes. Elements sorted by increasing absolute magnitude tend to
     * yield more accurate results.  If any stream element is a {@code NaN} or
     * the sum is at any point a {@code NaN} then the sum will be {@code NaN}.
     * This is a special case of a
     * <a href="package-summary.html#MutableReduction">reduction</a> and is
     * equivalent to:
     * <pre>{@code
     *     return reduce(0, Double::sum);
     * }</pre>
     *
     * @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#MutableReduction">reduction</a> and is
     * equivalent to:
     * <pre>{@code
     *     return reduce(Double::min);
     * }</pre>
     *
     * @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#MutableReduction">reduction</a> and is
     * equivalent to:
     * <pre>{@code
     *     return reduce(Double::max);
     * }</pre>
     *
     * @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#MutableReduction">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>.
     *
     * @return the count of elements in this stream
     */
    long count();

    /**
     * Returns an {@code OptionalDouble} describing the average of elements of
     * this stream, or an empty optional if this stream is empty.  The average
     * returned can vary depending upon the order in which elements are
     * encountered. This is due to accumulated rounding error in addition of
     * elements of differing magnitudes. Elements sorted by increasing absolute
     * magnitude tend to yield more accurate results. If any recorded value is
     * a {@code NaN} or the sum is at any point a {@code NaN} then the average
     * will be {@code NaN}. This is a special case of a
     * <a href="package-summary.html#MutableReduction">reduction</a>.
     *
     * @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#MutableReduction">reduction</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.
     *
     * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
     * terminal operation</a>.
     *
     * @param predicate a <a href="package-summary.html#NonInterference">non-interfering,
     *                  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.
     *
     * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
     * terminal operation</a>.
     *
     * @param predicate a <a href="package-summary.html#NonInterference">non-interfering,
     *                  stateless</a> predicate to apply to elements of this
     *                  stream
     * @return {@code true} if all elements of the stream match the provided
     * predicate 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.
     *
     * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting
     * terminal operation</a>.
     *
     * @param predicate a <a href="package-summary.html#NonInterference">non-interfering,
     *                  stateless</a> predicate to apply to elements of this
     *                  stream
     * @return {@code true} if no elements of the stream match the provided
     * predicate otherwise {@code false}
     */
    boolean noneMatch(DoublePredicate predicate);

    /**
     * Returns an {@link OptionalDouble} describing the first element of this
     * stream (in the encounter order), or an empty {@code OptionalDouble} if
     * the stream is empty.  If the stream has no encounter order, than 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 the first element
     * in the encounter order 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}.
     *
     * @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();
}