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 * 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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package java.util.stream;

import java.nio.charset.Charset;

import java.nio.file.Files;

import java.nio.file.Path;

import java.util.Arrays;

import java.util.Collection;

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.concurrent.ConcurrentHashMap;

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 the stream produced by applying the

     * provided mapping function to each element.  (If the result of the mapping

     * function is {@code null}, this is treated as if the result was an empty

     * 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 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 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>

     *

     * @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);

    /**

     * 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</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.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</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> type of the result

     * @param supplier 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</a>,

     *                    <a href="package-summary.html#Statelessness">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</a>,

     *                    <a href="package-summary.html#Statelessness">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> 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>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 {@code double}

     * values.

     *

     * <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