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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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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 double primitive specialization of Stream. 
The following example illustrates an aggregate operation using Stream and DoubleStream, computing the sum of the weights of the red widgets: 

    double sum = widgets.stream()
                        .filter(w -> w.getColor() == RED)
                        .mapToDouble(w -> w.getWeight())
                        .sum();
 See the class documentation for Stream and the package documentation for java.util.stream for additional
specification of streams, stream operations, stream pipelines, and
parallelism.
See Also:
Stream
java.util.stream
Since:
1.8/**
 * 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.
This is an intermediate
operation.
Params:
predicate – a non-interfering,
                 stateless
                 predicate to apply to each element to determine if it
                 should be included
Returns:
the new stream/**
     * 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.
This is an intermediate
operation.
Params:
mapper – a non-interfering,
              stateless
              function to apply to each element
Returns:
the new stream/**
     * 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 Stream consisting of the results of applying the given function to the elements of this stream. 
This is an 
    intermediate operation.
Params:
mapper – a non-interfering,
              stateless
              function to apply to each element
Type parameters:
<U> – the element type of the new stream
Returns:
the new stream/**
     * 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 IntStream consisting of the results of applying the given function to the elements of this stream. 
This is an intermediate
operation.
Params:
mapper – a non-interfering,
              stateless
              function to apply to each element
Returns:
the new stream/**
     * 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 LongStream consisting of the results of applying the given function to the elements of this stream. 
This is an intermediate
operation.
Params:
mapper – a non-interfering,
              stateless
              function to apply to each element
Returns:
the new stream/**
     * 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 closed after its contents have been placed into this stream. (If a mapped stream is null an empty stream is used, instead.) 
This is an intermediate
operation.
Params:
mapper – a non-interfering,
              stateless function to apply to each element which produces a DoubleStream of new values
See Also:
Stream.flatMap(Function)
Returns:
the new stream/**
     * 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 distinct elements of this stream. The elements are compared for equality according to Double.compare(double, double). 
This is a stateful
intermediate operation.
Returns:
the result stream/**
     * 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 Double.compare(double, double). 
This is a stateful
intermediate operation.
Returns:
the result stream/**
     * 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.
This is an intermediate
operation.
For parallel stream pipelines, the action may be called at
whatever time and in whatever thread the element is made available by the
upstream operation.  If the action modifies shared state,
it is responsible for providing the required synchronization.
Params:
action – a 
              non-interfering action to perform on the elements as
              they are consumed from the stream
API Note:
This method exists mainly to support debugging, where you want
to see the elements as they flow past a certain point in a pipeline:

    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();

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 findFirst, or in the example described in count), the action will not be invoked for those elements.
Returns:
the new stream/**
     * 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 maxSize in length. 
This is a short-circuiting
stateful intermediate operation.
Params:
maxSize – the number of elements the stream should be limited to
Throws:
IllegalArgumentException – if maxSize is negative
API Note:
 While limit() is generally a cheap operation on sequential stream pipelines, it can be quite expensive on ordered parallel pipelines, especially for large values of maxSize, since limit(n) is constrained to return not just any n elements, but the
first n elements in the encounter order. Using an unordered stream source (such as generate(DoubleSupplier)) or removing the ordering constraint with BaseStream<Double,DoubleStream>.unordered() may result in significant speedups of limit() in parallel pipelines, if the semantics of your situation permit. If consistency with encounter order is required, and you are experiencing poor performance or memory utilization with limit() in parallel pipelines, switching to sequential execution with sequential() may improve performance.
Returns:
the new stream/**
     * 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 n elements of the stream. If this stream contains fewer than n elements then an empty stream will be returned. 
This is a stateful
intermediate operation.
Params:
n – the number of leading elements to skip
Throws:
IllegalArgumentException – if n is negative
API Note:
 While skip() is generally a cheap operation on sequential stream pipelines, it can be quite expensive on ordered parallel pipelines, especially for large values of n, since skip(n) is constrained to skip not just any n elements, but the
first n elements in the encounter order. Using an unordered stream source (such as generate(DoubleSupplier)) or removing the ordering constraint with BaseStream<Double,DoubleStream>.unordered() may result in significant speedups of skip() in parallel pipelines, if the semantics of your situation permit. If consistency with encounter order is required, and you are experiencing poor performance or memory utilization with skip() in parallel pipelines, switching to sequential execution with sequential() may improve performance.
Returns:
the new stream/**
     * 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.
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.
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).
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).
This is a short-circuiting
stateful intermediate operation.
Params:
predicate – a non-interfering,
                 stateless
                 predicate to apply to elements to determine the longest
                 prefix of elements.
Implementation Requirements:
 The default implementation obtains the 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 BaseStream<Double,DoubleStream>.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.
API Note:
 While 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 generate(DoubleSupplier)) or removing the ordering constraint with BaseStream<Double,DoubleStream>.unordered() may result in significant speedups of 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 takeWhile() in parallel pipelines, switching to sequential execution with sequential() may improve performance.
Returns:
the new stream
Since:
9/**
     * 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.
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.
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).
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).
This is a stateful
intermediate operation.
Params:
predicate – a non-interfering,
                 stateless
                 predicate to apply to elements to determine the longest
                 prefix of elements.
Implementation Requirements:
 The default implementation obtains the 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 BaseStream<Double,DoubleStream>.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.
API Note:
 While 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 generate(DoubleSupplier)) or removing the ordering constraint with BaseStream<Double,DoubleStream>.unordered() may result in significant speedups of 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 dropWhile() in parallel pipelines, switching to sequential execution with sequential() may improve performance.
Returns:
the new stream
Since:
9/**
     * 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.
This is a terminal
operation.
For parallel stream pipelines, this operation does not
guarantee to respect the encounter order of the stream, as doing so
would sacrifice the benefit of parallelism.  For any given element, the
action may be performed at whatever time and in whatever thread the
library chooses.  If the action accesses shared state, it is
responsible for providing the required synchronization.
Params:
action – a 
              non-interfering action to perform on the elements/**
     * 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.
This is a terminal
operation.
Params:
action – a 
              non-interfering action to perform on the elements
See Also:
forEach(DoubleConsumer)/**
     * 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.
This is a terminal
operation.
Returns:
an array containing the elements of this stream/**
     * 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 reduction on the
elements of this stream, using the provided identity value and an
associative
accumulation function, and returns the reduced value.  This is equivalent
to:

    double result = identity;
    for (double element : this stream)
        result = accumulator.applyAsDouble(result, element)
    return result;

but is not constrained to execute sequentially.
The identity value must be an identity for the accumulator function. This means that for all x, accumulator.apply(identity, x) is equal to x. The accumulator function must be an associative function.
This is a terminal
operation.
Params:
identity – the identity value for the accumulating function
op – an associative,
          non-interfering,
          stateless
          function for combining two values
See Also:
sum()
min()
max()
average()
API Note:
Sum, min, max, and average are all special cases of reduction.
Summing a stream of numbers can be expressed as:

    double sum = numbers.reduce(0, (a, b) -> a+b);

or more compactly:

    double sum = numbers.reduce(0, Double::sum);

While this may seem a more roundabout way to perform an aggregation
compared to simply mutating a running total in a loop, reduction
operations parallelize more gracefully, without needing additional
synchronization and with greatly reduced risk of data races.
Returns:
the result of the reduction/**
     * 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 reduction on the
elements of this stream, using an
associative accumulation function, and returns an OptionalDouble describing the reduced value, if any. This is equivalent to: 

    boolean foundAny = false;
    double result = null;
    for (double element : this stream) {
        if (!foundAny) {
            foundAny = true;
            result = element;
        }
        else
            result = accumulator.applyAsDouble(result, element);
    }
    return foundAny ? OptionalDouble.of(result) : OptionalDouble.empty();

but is not constrained to execute sequentially.
The accumulator function must be an associative function.
This is a terminal
operation.
Params:
op – an associative,
          non-interfering,
          stateless
          function for combining two values
See Also:
reduce(double, DoubleBinaryOperator)
Returns:
the result of the reduction/**
     * 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 mutable
reduction operation on the elements of this stream. A mutable reduction is one in which the reduced value is a mutable result container, such as an ArrayList, and elements are incorporated by updating the state of the result rather than by replacing the result. This produces a result equivalent to: 

    R result = supplier.get();
    for (double element : this stream)
        accumulator.accept(result, element);
    return result;

Like reduce(double, DoubleBinaryOperator), collect operations can be parallelized without requiring additional synchronization. 
This is a terminal
operation.
Params:
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.
accumulator – an associative,
                   non-interfering,
                   stateless
                   function that must fold an element into a result
                   container.
combiner – an associative,
                   non-interfering,
                   stateless
                   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.
Type parameters:
<R> – the type of the mutable result container
See Also:
Stream.collect(Supplier, BiConsumer, BiConsumer)
Returns:
the result of the reduction/**
     * 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 reduction. If
floating-point summation were exact, this method would be
equivalent to:

    return reduce(0, Double::sum);

However, since floating-point summation is not exact, the above
code is not necessarily equivalent to the summation computation
done by this method.
The value of a floating-point sum is a function both of the input values as well as the order of addition operations. The order of addition operations of this method is intentionally not defined to allow for implementation flexibility to improve the speed and accuracy of the computed result. In particular, this method may be implemented using compensated summation or other technique to reduce the error bound in the numerical sum compared to a simple summation of double values. 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. 
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:

If any element is a NaN, then the final sum will be
NaN.
If the elements contain one or more infinities, the
sum will be infinite or NaN.

If the elements contain infinities of opposite sign,
the sum will be NaN.
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.


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
not guaranteed to be preserved in the final sum.
This is a terminal
operation.
API Note:
Elements sorted by increasing absolute magnitude tend
to yield more accurate results.
Returns:
the sum of elements in this stream/**
     * 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 OptionalDouble describing the minimum element of this stream, or an empty OptionalDouble if this stream is empty. The minimum element will be Double.NaN if any stream element was NaN. Unlike the numerical comparison operators, this method considers negative zero to be strictly smaller than positive zero. This is a special case of a reduction and is
equivalent to:

    return reduce(Double::min);

This is a terminal
operation.
Returns:
an OptionalDouble containing the minimum element of this stream, or an empty optional if the stream is empty/**
     * 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 OptionalDouble describing the maximum element of this stream, or an empty OptionalDouble if this stream is empty. The maximum element will be Double.NaN if any stream element was NaN. Unlike the numerical comparison operators, this method considers negative zero to be strictly smaller than positive zero. This is a special case of a reduction and is
equivalent to:

    return reduce(Double::max);

This is a terminal
operation.
Returns:
an OptionalDouble containing the maximum element of this stream, or an empty optional if the stream is empty/**
     * 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 reduction and is
equivalent to:

    return mapToLong(e -> 1L).sum();

This is a terminal operation.
API Note:

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:

    DoubleStream s = DoubleStream.of(1, 2, 3, 4);
    long count = s.peek(System.out::println).count();
 The number of elements covered by the stream source is known and the intermediate operation, peek, does not inject into or remove elements from the stream (as may be the case for flatMap or 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.
Returns:
the count of elements in this stream/**
     * 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 OptionalDouble describing the arithmetic mean of elements of this stream, or an empty optional if this stream is empty. 
The computed average can vary numerically and have the special case behavior as computing the sum; see sum for details. 
The average is a special case of a reduction.
This is a terminal
operation.
API Note:
Elements sorted by increasing absolute magnitude tend
to yield more accurate results.
Returns:
an OptionalDouble containing the average element of this stream, or an empty optional if the stream is empty/**
     * 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 DoubleSummaryStatistics describing various summary data about the elements of this stream. This is a special case of a reduction.
This is a terminal
operation.
Returns:
a DoubleSummaryStatistics describing various summary data about the elements of this stream/**
     * 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 false is returned and the predicate is not evaluated. 
This is a short-circuiting
terminal operation.
Params:
predicate – a non-interfering,
                 stateless
                 predicate to apply to elements of this stream
API Note:

This method evaluates the existential quantification of the
predicate over the elements of the stream (for some x P(x)).
Returns:
true if any elements of the stream match the provided predicate, otherwise false/**
     * 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 true is returned and the predicate is not evaluated. 
This is a short-circuiting
terminal operation.
Params:
predicate – a non-interfering,
                 stateless
                 predicate to apply to elements of this stream
API Note:

This method evaluates the universal quantification 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 vacuously
satisfied and is always true (regardless of P(x)).
Returns:
true if either all elements of the stream match the provided predicate or the stream is empty, otherwise false/**
     * 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 true is returned and the predicate is not evaluated. 
This is a short-circuiting
terminal operation.
Params:
predicate – a non-interfering,
                 stateless
                 predicate to apply to elements of this stream
API Note:

This method evaluates the universal quantification 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 true, regardless of P(x).
Returns:
true if either no elements of the stream match the provided predicate or the stream is empty, otherwise false/**
     * 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 OptionalDouble describing the first element of this stream, or an empty OptionalDouble if the stream is empty. If the stream has no encounter order, then any element may be returned. 
This is a short-circuiting
terminal operation.
Returns:
an OptionalDouble describing the first element of this stream, or an empty OptionalDouble if the stream is empty/**
     * 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 OptionalDouble describing some element of the stream, or an empty OptionalDouble if the stream is empty. 
This is a short-circuiting
terminal operation.
The behavior of this operation is explicitly nondeterministic; it is free to select any element in the stream. This is to allow for maximal performance in parallel operations; the cost is that multiple invocations on the same source may not return the same result. (If a stable result is desired, use findFirst() instead.) 
See Also:
findFirst()
Returns:
an OptionalDouble describing some element of this stream, or an empty OptionalDouble if the stream is empty/**
     * 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 Stream consisting of the elements of this stream, boxed to Double. 
This is an intermediate
operation.
Returns:
a Stream consistent of the elements of this stream, each boxed to a Double/**
     * 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 DoubleStream. 
Returns:
a stream builder/**
     * Returns a builder for a {@code DoubleStream}.
     *
     * @return a stream builder
     */
    public static Builder builder() {
        return new Streams.DoubleStreamBuilderImpl();
    }

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

    
Returns a sequential DoubleStream containing a single element. 
Params:
t – the single element
Returns:
a singleton sequential stream/**
     * 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.
Params:
values – the elements of the new stream
Returns:
the new stream/**
     * 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 DoubleStream produced by iterative application of a function f to an initial element seed, producing a Stream consisting of seed, f(seed), f(f(seed)), etc. 
The first element (position 0) in the DoubleStream will be the provided seed. For n > 0, the element at position n, will be the result of applying the function f to the element at position n - 1. 
The action of applying f for one element happens-before the action of applying f for subsequent elements. For any given element the action may be performed in whatever thread the library chooses. 
Params:
seed – the initial element
f – a function to be applied to the previous element to produce
         a new element
Returns:
a new sequential DoubleStream/**
     * 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 DoubleStream produced by iterative application of the given next function to an initial element, conditioned on satisfying the given hasNext predicate. The stream terminates as soon as the hasNext predicate returns false. 
DoubleStream.iterate should produce the same sequence of elements as produced by the corresponding for-loop: 

    for (double index=seed; hasNext.test(index); index = next.applyAsDouble(index)) {
        ...
    }

The resulting sequence may be empty if the hasNext predicate does not hold on the seed value. Otherwise the first element will be the supplied seed value, the next element (if present) will be the result of applying the next function to the seed value, and so on iteratively until the hasNext predicate indicates that the stream should terminate. 
The action of applying the hasNext predicate to an element happens-before the action of applying the next function to that element. The action of applying the next function for one element happens-before the action of applying the hasNext predicate for subsequent elements. For any given element an action may be performed in whatever thread the library chooses. 
Params:
seed – the initial element
hasNext – a predicate to apply to elements to determine when the
               stream must terminate.
next – a function to be applied to the previous element to produce
            a new element
Returns:
a new sequential DoubleStream
Since:
9/**
     * 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 DoubleSupplier. This is suitable for generating constant streams, streams of random elements, etc. 
Params:
s – the DoubleSupplier for generated elements
Returns:
a new infinite sequential unordered DoubleStream/**
     * 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.
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.
Params:
a – the first stream
b – the second stream
Implementation Note:
 Use caution when constructing streams from repeated concatenation. Accessing an element of a deeply concatenated stream can result in deep call chains, or even StackOverflowError.
API Note:

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:

    DoubleStream concat = Stream.of(s1, s2, s3, s4).flatMapToDouble(s -> s);
Returns:
the concatenation of the two input streams/**
     * 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 DoubleStream. 
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 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 Also:
DoubleStream.builder()
Since:
1.8/**
     * 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/**
         * 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.
Params:
t – the element to add
Throws:
IllegalStateException – if the builder has already transitioned
to the built state
Implementation Requirements:

The default implementation behaves as if:

    accept(t)
    return this;
Returns:
this builder/**
         * 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 IllegalStateException is thrown if there are further attempts to operate on the builder after it has entered the built state. 
Throws:
IllegalStateException – if the builder has already transitioned
to the built state
Returns:
the built stream/**
         * 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();
    }
}