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 * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
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 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
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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 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:
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:
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:
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:
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:
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:
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:
See Also:
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();

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>
     *
     * @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:
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:
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);

    
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:
/**
     * 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:
See Also:
/**
     * 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:
See Also:
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:
See Also:
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 result container. For a
                parallel execution, this function may be called
                multiple times and must return a fresh value each time.
  • accumulator – an associative,
                   non-interfering,
                   stateless
                   function for incorporating an additional element into a result
  • combiner – an associative,
                   non-interfering,
                   stateless
                   function for combining two values, which must be
                   compatible with the accumulator function
Type parameters:
  • <R> – type of the result
See Also:
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> 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 reduction. If
floating-point summation were exact, this method would be
equivalent to:


    return reduce(0, Double::sum);


However, since floating-point summation is not exact, the above
code is not necessarily equivalent to the summation computation
done by this method.

If any stream element is a NaN or the sum is at any point a NaN then the sum will be NaN. The value of a floating-point sum is a function both of the input values as well as the order of addition operations. The order of addition operations of this method is intentionally not defined to allow for implementation flexibility to improve the speed and accuracy of the computed result. In particular, this method may be implemented using compensated summation or other technique to reduce the error bound in the numerical sum compared to a simple summation of double values. 
This is a terminal
operation.

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>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 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.

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>.
     *
     * @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. If any recorded value is a NaN or the sum is at any point a NaN then the average will be NaN. 
The average returned can vary depending upon the order in which values are recorded. This method may be implemented using compensated summation or other technique to reduce the error bound in the 
numerical sum used to compute the average. 
The average is a special case of a reduction.

This is a terminal
operation.

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.
     *
     * If any recorded value is a NaN or the sum is at any point a NaN
     * then the average will be NaN.
     *
     * <p>The average returned can vary depending upon the order in
     * which values are recorded.
     *
     * This method may be implemented using compensated summation or
     * other technique to reduce the error bound in the {@link #sum
     * numerical sum} used to compute the average.
     *
     *  <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:
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:
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:
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:
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. 
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}.
     *
     * @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);
        final PrimitiveIterator.OfDouble iterator = new PrimitiveIterator.OfDouble() {
            double t = seed;

            @Override
            public boolean hasNext() {
                return true;
            }

            @Override
            public double nextDouble() {
                double v = t;
                t = f.applyAsDouble(t);
                return v;
            }
        };
        return StreamSupport.doubleStream(Spliterators.spliteratorUnknownSize(
                iterator,
                Spliterator.ORDERED | Spliterator.IMMUTABLE | Spliterator.NONNULL), 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.

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 StackOverflowException.
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.
     *
     * @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 StackOverflowException}.
     *
     * @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:
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:
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:
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();
    }
}