| /* |
| * Copyright (c) 2012, 2020, Oracle and/or its affiliates. All rights reserved. |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle in the LICENSE file that accompanied this code. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| package java.util.stream; |
| |
| import java.util.Arrays; |
| import java.util.DoubleSummaryStatistics; |
| import java.util.Objects; |
| import java.util.OptionalDouble; |
| import java.util.PrimitiveIterator; |
| import java.util.Spliterator; |
| import java.util.Spliterators; |
| import java.util.function.BiConsumer; |
| import java.util.function.DoubleBinaryOperator; |
| import java.util.function.DoubleConsumer; |
| import java.util.function.DoubleFunction; |
| import java.util.function.DoublePredicate; |
| import java.util.function.DoubleSupplier; |
| import java.util.function.DoubleToIntFunction; |
| import java.util.function.DoubleToLongFunction; |
| import java.util.function.DoubleUnaryOperator; |
| import java.util.function.Function; |
| import java.util.function.ObjDoubleConsumer; |
| import java.util.function.Supplier; |
| |
| /** |
| * A sequence of primitive double-valued elements supporting sequential and parallel |
| * aggregate operations. This is the {@code double} primitive specialization of |
| * {@link Stream}. |
| * |
| * <p>The following example illustrates an aggregate operation using |
| * {@link Stream} and {@link DoubleStream}, computing the sum of the weights of the |
| * red widgets: |
| * |
| * <pre>{@code |
| * double sum = widgets.stream() |
| * .filter(w -> w.getColor() == RED) |
| * .mapToDouble(w -> w.getWeight()) |
| * .sum(); |
| * }</pre> |
| * |
| * See the class documentation for {@link Stream} and the package documentation |
| * for <a href="package-summary.html">java.util.stream</a> for additional |
| * specification of streams, stream operations, stream pipelines, and |
| * parallelism. |
| * |
| * @since 1.8 |
| * @see Stream |
| * @see <a href="package-summary.html">java.util.stream</a> |
| */ |
| public interface DoubleStream extends BaseStream<Double, DoubleStream> { |
| |
| /** |
| * Returns a stream consisting of the elements of this stream that match |
| * the given predicate. |
| * |
| * <p>This is an <a href="package-summary.html#StreamOps">intermediate |
| * operation</a>. |
| * |
| * @param predicate a <a href="package-summary.html#NonInterference">non-interfering</a>, |
| * <a href="package-summary.html#Statelessness">stateless</a> |
| * predicate to apply to each element to determine if it |
| * should be included |
| * @return the new stream |
| */ |
| DoubleStream filter(DoublePredicate predicate); |
| |
| /** |
| * Returns a stream consisting of the results of applying the given |
| * function to the elements of this stream. |
| * |
| * <p>This is an <a href="package-summary.html#StreamOps">intermediate |
| * operation</a>. |
| * |
| * @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>, |
| * <a href="package-summary.html#Statelessness">stateless</a> |
| * function to apply to each element |
| * @return the new stream |
| */ |
| DoubleStream map(DoubleUnaryOperator mapper); |
| |
| /** |
| * Returns an object-valued {@code Stream} consisting of the results of |
| * applying the given function to the elements of this stream. |
| * |
| * <p>This is an <a href="package-summary.html#StreamOps"> |
| * intermediate operation</a>. |
| * |
| * @param <U> the element type of the new stream |
| * @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>, |
| * <a href="package-summary.html#Statelessness">stateless</a> |
| * function to apply to each element |
| * @return the new stream |
| */ |
| <U> Stream<U> mapToObj(DoubleFunction<? extends U> mapper); |
| |
| /** |
| * Returns an {@code IntStream} consisting of the results of applying the |
| * given function to the elements of this stream. |
| * |
| * <p>This is an <a href="package-summary.html#StreamOps">intermediate |
| * operation</a>. |
| * |
| * @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>, |
| * <a href="package-summary.html#Statelessness">stateless</a> |
| * function to apply to each element |
| * @return the new stream |
| */ |
| IntStream mapToInt(DoubleToIntFunction mapper); |
| |
| /** |
| * Returns a {@code LongStream} consisting of the results of applying the |
| * given function to the elements of this stream. |
| * |
| * <p>This is an <a href="package-summary.html#StreamOps">intermediate |
| * operation</a>. |
| * |
| * @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>, |
| * <a href="package-summary.html#Statelessness">stateless</a> |
| * function to apply to each element |
| * @return the new stream |
| */ |
| LongStream mapToLong(DoubleToLongFunction mapper); |
| |
| /** |
| * Returns a stream consisting of the results of replacing each element of |
| * this stream with the contents of a mapped stream produced by applying |
| * the provided mapping function to each element. Each mapped stream is |
| * {@link java.util.stream.BaseStream#close() closed} after its contents |
| * have been placed into this stream. (If a mapped stream is {@code null} |
| * an empty stream is used, instead.) |
| * |
| * <p>This is an <a href="package-summary.html#StreamOps">intermediate |
| * operation</a>. |
| * |
| * @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>, |
| * <a href="package-summary.html#Statelessness">stateless</a> |
| * function to apply to each element which produces a |
| * {@code DoubleStream} of new values |
| * @return the new stream |
| * @see Stream#flatMap(Function) |
| */ |
| DoubleStream flatMap(DoubleFunction<? extends DoubleStream> mapper); |
| |
| /** |
| * Returns a stream consisting of the results of replacing each element of |
| * this stream with multiple elements, specifically zero or more elements. |
| * Replacement is performed by applying the provided mapping function to each |
| * element in conjunction with a {@linkplain DoubleConsumer consumer} argument |
| * that accepts replacement elements. The mapping function calls the consumer |
| * zero or more times to provide the replacement elements. |
| * |
| * <p>This is an <a href="package-summary.html#StreamOps">intermediate |
| * operation</a>. |
| * |
| * <p>If the {@linkplain DoubleConsumer consumer} argument is used outside the scope of |
| * its application to the mapping function, the results are undefined. |
| * |
| * @implSpec |
| * The default implementation invokes {@link #flatMap flatMap} on this stream, |
| * passing a function that behaves as follows. First, it calls the mapper function |
| * with a {@code DoubleConsumer} that accumulates replacement elements into a newly created |
| * internal buffer. When the mapper function returns, it creates a {@code DoubleStream} from the |
| * internal buffer. Finally, it returns this stream to {@code flatMap}. |
| * |
| * @param mapper a <a href="package-summary.html#NonInterference">non-interfering</a>, |
| * <a href="package-summary.html#Statelessness">stateless</a> |
| * function that generates replacement elements |
| * @return the new stream |
| * @see Stream#mapMulti Stream.mapMulti |
| * @since 16 |
| */ |
| default DoubleStream mapMulti(DoubleMapMultiConsumer mapper) { |
| Objects.requireNonNull(mapper); |
| return flatMap(e -> { |
| SpinedBuffer.OfDouble buffer = new SpinedBuffer.OfDouble(); |
| mapper.accept(e, buffer); |
| return StreamSupport.doubleStream(buffer.spliterator(), false); |
| }); |
| } |
| |
| /** |
| * Returns a stream consisting of the distinct elements of this stream. The |
| * elements are compared for equality according to |
| * {@link java.lang.Double#compare(double, double)}. |
| * |
| * <p>This is a <a href="package-summary.html#StreamOps">stateful |
| * intermediate operation</a>. |
| * |
| * @return the result stream |
| */ |
| DoubleStream distinct(); |
| |
| /** |
| * Returns a stream consisting of the elements of this stream in sorted |
| * order. The elements are compared for equality according to |
| * {@link java.lang.Double#compare(double, double)}. |
| * |
| * <p>This is a <a href="package-summary.html#StreamOps">stateful |
| * intermediate operation</a>. |
| * |
| * @return the result stream |
| */ |
| DoubleStream sorted(); |
| |
| /** |
| * Returns a stream consisting of the elements of this stream, additionally |
| * performing the provided action on each element as elements are consumed |
| * from the resulting stream. |
| * |
| * <p>This is an <a href="package-summary.html#StreamOps">intermediate |
| * operation</a>. |
| * |
| * <p>For parallel stream pipelines, the action may be called at |
| * whatever time and in whatever thread the element is made available by the |
| * upstream operation. If the action modifies shared state, |
| * it is responsible for providing the required synchronization. |
| * |
| * @apiNote This method exists mainly to support debugging, where you want |
| * to see the elements as they flow past a certain point in a pipeline: |
| * <pre>{@code |
| * DoubleStream.of(1, 2, 3, 4) |
| * .filter(e -> e > 2) |
| * .peek(e -> System.out.println("Filtered value: " + e)) |
| * .map(e -> e * e) |
| * .peek(e -> System.out.println("Mapped value: " + e)) |
| * .sum(); |
| * }</pre> |
| * |
| * <p>In cases where the stream implementation is able to optimize away the |
| * production of some or all the elements (such as with short-circuiting |
| * operations like {@code findFirst}, or in the example described in |
| * {@link #count}), the action will not be invoked for those elements. |
| * |
| * @param action a <a href="package-summary.html#NonInterference"> |
| * non-interfering</a> action to perform on the elements as |
| * they are consumed from the stream |
| * @return the new stream |
| */ |
| DoubleStream peek(DoubleConsumer action); |
| |
| /** |
| * Returns a stream consisting of the elements of this stream, truncated |
| * to be no longer than {@code maxSize} in length. |
| * |
| * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting |
| * stateful intermediate operation</a>. |
| * |
| * @apiNote |
| * While {@code limit()} is generally a cheap operation on sequential |
| * stream pipelines, it can be quite expensive on ordered parallel pipelines, |
| * especially for large values of {@code maxSize}, since {@code limit(n)} |
| * is constrained to return not just any <em>n</em> elements, but the |
| * <em>first n</em> elements in the encounter order. Using an unordered |
| * stream source (such as {@link #generate(DoubleSupplier)}) or removing the |
| * ordering constraint with {@link #unordered()} may result in significant |
| * speedups of {@code limit()} in parallel pipelines, if the semantics of |
| * your situation permit. If consistency with encounter order is required, |
| * and you are experiencing poor performance or memory utilization with |
| * {@code limit()} in parallel pipelines, switching to sequential execution |
| * with {@link #sequential()} may improve performance. |
| * |
| * @param maxSize the number of elements the stream should be limited to |
| * @return the new stream |
| * @throws IllegalArgumentException if {@code maxSize} is negative |
| */ |
| DoubleStream limit(long maxSize); |
| |
| /** |
| * Returns a stream consisting of the remaining elements of this stream |
| * after discarding the first {@code n} elements of the stream. |
| * If this stream contains fewer than {@code n} elements then an |
| * empty stream will be returned. |
| * |
| * <p>This is a <a href="package-summary.html#StreamOps">stateful |
| * intermediate operation</a>. |
| * |
| * @apiNote |
| * While {@code skip()} is generally a cheap operation on sequential |
| * stream pipelines, it can be quite expensive on ordered parallel pipelines, |
| * especially for large values of {@code n}, since {@code skip(n)} |
| * is constrained to skip not just any <em>n</em> elements, but the |
| * <em>first n</em> elements in the encounter order. Using an unordered |
| * stream source (such as {@link #generate(DoubleSupplier)}) or removing the |
| * ordering constraint with {@link #unordered()} may result in significant |
| * speedups of {@code skip()} in parallel pipelines, if the semantics of |
| * your situation permit. If consistency with encounter order is required, |
| * and you are experiencing poor performance or memory utilization with |
| * {@code skip()} in parallel pipelines, switching to sequential execution |
| * with {@link #sequential()} may improve performance. |
| * |
| * @param n the number of leading elements to skip |
| * @return the new stream |
| * @throws IllegalArgumentException if {@code n} is negative |
| */ |
| DoubleStream skip(long n); |
| |
| /** |
| * Returns, if this stream is ordered, a stream consisting of the longest |
| * prefix of elements taken from this stream that match the given predicate. |
| * Otherwise returns, if this stream is unordered, a stream consisting of a |
| * subset of elements taken from this stream that match the given predicate. |
| * |
| * <p>If this stream is ordered then the longest prefix is a contiguous |
| * sequence of elements of this stream that match the given predicate. The |
| * first element of the sequence is the first element of this stream, and |
| * the element immediately following the last element of the sequence does |
| * not match the given predicate. |
| * |
| * <p>If this stream is unordered, and some (but not all) elements of this |
| * stream match the given predicate, then the behavior of this operation is |
| * nondeterministic; it is free to take any subset of matching elements |
| * (which includes the empty set). |
| * |
| * <p>Independent of whether this stream is ordered or unordered if all |
| * elements of this stream match the given predicate then this operation |
| * takes all elements (the result is the same as the input), or if no |
| * elements of the stream match the given predicate then no elements are |
| * taken (the result is an empty stream). |
| * |
| * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting |
| * stateful intermediate operation</a>. |
| * |
| * @implSpec |
| * The default implementation obtains the {@link #spliterator() spliterator} |
| * of this stream, wraps that spliterator so as to support the semantics |
| * of this operation on traversal, and returns a new stream associated with |
| * the wrapped spliterator. The returned stream preserves the execution |
| * characteristics of this stream (namely parallel or sequential execution |
| * as per {@link #isParallel()}) but the wrapped spliterator may choose to |
| * not support splitting. When the returned stream is closed, the close |
| * handlers for both the returned and this stream are invoked. |
| * |
| * @apiNote |
| * While {@code takeWhile()} is generally a cheap operation on sequential |
| * stream pipelines, it can be quite expensive on ordered parallel |
| * pipelines, since the operation is constrained to return not just any |
| * valid prefix, but the longest prefix of elements in the encounter order. |
| * Using an unordered stream source (such as |
| * {@link #generate(DoubleSupplier)}) or removing the ordering constraint |
| * with {@link #unordered()} may result in significant speedups of |
| * {@code takeWhile()} in parallel pipelines, if the semantics of your |
| * situation permit. If consistency with encounter order is required, and |
| * you are experiencing poor performance or memory utilization with |
| * {@code takeWhile()} in parallel pipelines, switching to sequential |
| * execution with {@link #sequential()} may improve performance. |
| * |
| * @param predicate a <a href="package-summary.html#NonInterference">non-interfering</a>, |
| * <a href="package-summary.html#Statelessness">stateless</a> |
| * predicate to apply to elements to determine the longest |
| * prefix of elements. |
| * @return the new stream |
| * @since 9 |
| */ |
| default DoubleStream takeWhile(DoublePredicate predicate) { |
| Objects.requireNonNull(predicate); |
| // Reuses the unordered spliterator, which, when encounter is present, |
| // is safe to use as long as it configured not to split |
| return StreamSupport.doubleStream( |
| new WhileOps.UnorderedWhileSpliterator.OfDouble.Taking(spliterator(), true, predicate), |
| isParallel()).onClose(this::close); |
| } |
| |
| /** |
| * Returns, if this stream is ordered, a stream consisting of the remaining |
| * elements of this stream after dropping the longest prefix of elements |
| * that match the given predicate. Otherwise returns, if this stream is |
| * unordered, a stream consisting of the remaining elements of this stream |
| * after dropping a subset of elements that match the given predicate. |
| * |
| * <p>If this stream is ordered then the longest prefix is a contiguous |
| * sequence of elements of this stream that match the given predicate. The |
| * first element of the sequence is the first element of this stream, and |
| * the element immediately following the last element of the sequence does |
| * not match the given predicate. |
| * |
| * <p>If this stream is unordered, and some (but not all) elements of this |
| * stream match the given predicate, then the behavior of this operation is |
| * nondeterministic; it is free to drop any subset of matching elements |
| * (which includes the empty set). |
| * |
| * <p>Independent of whether this stream is ordered or unordered if all |
| * elements of this stream match the given predicate then this operation |
| * drops all elements (the result is an empty stream), or if no elements of |
| * the stream match the given predicate then no elements are dropped (the |
| * result is the same as the input). |
| * |
| * <p>This is a <a href="package-summary.html#StreamOps">stateful |
| * intermediate operation</a>. |
| * |
| * @implSpec |
| * The default implementation obtains the {@link #spliterator() spliterator} |
| * of this stream, wraps that spliterator so as to support the semantics |
| * of this operation on traversal, and returns a new stream associated with |
| * the wrapped spliterator. The returned stream preserves the execution |
| * characteristics of this stream (namely parallel or sequential execution |
| * as per {@link #isParallel()}) but the wrapped spliterator may choose to |
| * not support splitting. When the returned stream is closed, the close |
| * handlers for both the returned and this stream are invoked. |
| * |
| * @apiNote |
| * While {@code dropWhile()} is generally a cheap operation on sequential |
| * stream pipelines, it can be quite expensive on ordered parallel |
| * pipelines, since the operation is constrained to return not just any |
| * valid prefix, but the longest prefix of elements in the encounter order. |
| * Using an unordered stream source (such as |
| * {@link #generate(DoubleSupplier)}) or removing the ordering constraint |
| * with {@link #unordered()} may result in significant speedups of |
| * {@code dropWhile()} in parallel pipelines, if the semantics of your |
| * situation permit. If consistency with encounter order is required, and |
| * you are experiencing poor performance or memory utilization with |
| * {@code dropWhile()} in parallel pipelines, switching to sequential |
| * execution with {@link #sequential()} may improve performance. |
| * |
| * @param predicate a <a href="package-summary.html#NonInterference">non-interfering</a>, |
| * <a href="package-summary.html#Statelessness">stateless</a> |
| * predicate to apply to elements to determine the longest |
| * prefix of elements. |
| * @return the new stream |
| * @since 9 |
| */ |
| default DoubleStream dropWhile(DoublePredicate predicate) { |
| Objects.requireNonNull(predicate); |
| // Reuses the unordered spliterator, which, when encounter is present, |
| // is safe to use as long as it configured not to split |
| return StreamSupport.doubleStream( |
| new WhileOps.UnorderedWhileSpliterator.OfDouble.Dropping(spliterator(), true, predicate), |
| isParallel()).onClose(this::close); |
| } |
| |
| /** |
| * Performs an action for each element of this stream. |
| * |
| * <p>This is a <a href="package-summary.html#StreamOps">terminal |
| * operation</a>. |
| * |
| * <p>For parallel stream pipelines, this operation does <em>not</em> |
| * guarantee to respect the encounter order of the stream, as doing so |
| * would sacrifice the benefit of parallelism. For any given element, the |
| * action may be performed at whatever time and in whatever thread the |
| * library chooses. If the action accesses shared state, it is |
| * responsible for providing the required synchronization. |
| * |
| * @param action a <a href="package-summary.html#NonInterference"> |
| * non-interfering</a> action to perform on the elements |
| */ |
| void forEach(DoubleConsumer action); |
| |
| /** |
| * Performs an action for each element of this stream, guaranteeing that |
| * each element is processed in encounter order for streams that have a |
| * defined encounter order. |
| * |
| * <p>This is a <a href="package-summary.html#StreamOps">terminal |
| * operation</a>. |
| * |
| * @param action a <a href="package-summary.html#NonInterference"> |
| * non-interfering</a> action to perform on the elements |
| * @see #forEach(DoubleConsumer) |
| */ |
| void forEachOrdered(DoubleConsumer action); |
| |
| /** |
| * Returns an array containing the elements of this stream. |
| * |
| * <p>This is a <a href="package-summary.html#StreamOps">terminal |
| * operation</a>. |
| * |
| * @return an array containing the elements of this stream |
| */ |
| double[] toArray(); |
| |
| /** |
| * Performs a <a href="package-summary.html#Reduction">reduction</a> on the |
| * elements of this stream, using the provided identity value and an |
| * <a href="package-summary.html#Associativity">associative</a> |
| * accumulation function, and returns the reduced value. This is equivalent |
| * to: |
| * <pre>{@code |
| * double result = identity; |
| * for (double element : this stream) |
| * result = accumulator.applyAsDouble(result, element) |
| * return result; |
| * }</pre> |
| * |
| * but is not constrained to execute sequentially. |
| * |
| * <p>The {@code identity} value must be an identity for the accumulator |
| * function. This means that for all {@code x}, |
| * {@code accumulator.apply(identity, x)} is equal to {@code x}. |
| * The {@code accumulator} function must be an |
| * <a href="package-summary.html#Associativity">associative</a> function. |
| * |
| * <p>This is a <a href="package-summary.html#StreamOps">terminal |
| * operation</a>. |
| * |
| * @apiNote Sum, min, max, and average are all special cases of reduction. |
| * Summing a stream of numbers can be expressed as: |
| * |
| * <pre>{@code |
| * double sum = numbers.reduce(0, (a, b) -> a+b); |
| * }</pre> |
| * |
| * or more compactly: |
| * |
| * <pre>{@code |
| * double sum = numbers.reduce(0, Double::sum); |
| * }</pre> |
| * |
| * <p>While this may seem a more roundabout way to perform an aggregation |
| * compared to simply mutating a running total in a loop, reduction |
| * operations parallelize more gracefully, without needing additional |
| * synchronization and with greatly reduced risk of data races. |
| * |
| * @param identity the identity value for the accumulating function |
| * @param op an <a href="package-summary.html#Associativity">associative</a>, |
| * <a href="package-summary.html#NonInterference">non-interfering</a>, |
| * <a href="package-summary.html#Statelessness">stateless</a> |
| * function for combining two values |
| * @return the result of the reduction |
| * @see #sum() |
| * @see #min() |
| * @see #max() |
| * @see #average() |
| */ |
| double reduce(double identity, DoubleBinaryOperator op); |
| |
| /** |
| * Performs a <a href="package-summary.html#Reduction">reduction</a> on the |
| * elements of this stream, using an |
| * <a href="package-summary.html#Associativity">associative</a> accumulation |
| * function, and returns an {@code OptionalDouble} describing the reduced |
| * value, if any. This is equivalent to: |
| * <pre>{@code |
| * boolean foundAny = false; |
| * double result = null; |
| * for (double element : this stream) { |
| * if (!foundAny) { |
| * foundAny = true; |
| * result = element; |
| * } |
| * else |
| * result = accumulator.applyAsDouble(result, element); |
| * } |
| * return foundAny ? OptionalDouble.of(result) : OptionalDouble.empty(); |
| * }</pre> |
| * |
| * but is not constrained to execute sequentially. |
| * |
| * <p>The {@code accumulator} function must be an |
| * <a href="package-summary.html#Associativity">associative</a> function. |
| * |
| * <p>This is a <a href="package-summary.html#StreamOps">terminal |
| * operation</a>. |
| * |
| * @param op an <a href="package-summary.html#Associativity">associative</a>, |
| * <a href="package-summary.html#NonInterference">non-interfering</a>, |
| * <a href="package-summary.html#Statelessness">stateless</a> |
| * function for combining two values |
| * @return the result of the reduction |
| * @see #reduce(double, DoubleBinaryOperator) |
| */ |
| OptionalDouble reduce(DoubleBinaryOperator op); |
| |
| /** |
| * Performs a <a href="package-summary.html#MutableReduction">mutable |
| * reduction</a> operation on the elements of this stream. A mutable |
| * reduction is one in which the reduced value is a mutable result container, |
| * such as an {@code ArrayList}, and elements are incorporated by updating |
| * the state of the result rather than by replacing the result. This |
| * produces a result equivalent to: |
| * <pre>{@code |
| * R result = supplier.get(); |
| * for (double element : this stream) |
| * accumulator.accept(result, element); |
| * return result; |
| * }</pre> |
| * |
| * <p>Like {@link #reduce(double, DoubleBinaryOperator)}, {@code collect} |
| * operations can be parallelized without requiring additional |
| * synchronization. |
| * |
| * <p>This is a <a href="package-summary.html#StreamOps">terminal |
| * operation</a>. |
| * |
| * @param <R> the type of the mutable result container |
| * @param supplier a function that creates a new mutable result container. |
| * For a parallel execution, this function may be called |
| * multiple times and must return a fresh value each time. |
| * @param accumulator an <a href="package-summary.html#Associativity">associative</a>, |
| * <a href="package-summary.html#NonInterference">non-interfering</a>, |
| * <a href="package-summary.html#Statelessness">stateless</a> |
| * function that must fold an element into a result |
| * container. |
| * @param combiner an <a href="package-summary.html#Associativity">associative</a>, |
| * <a href="package-summary.html#NonInterference">non-interfering</a>, |
| * <a href="package-summary.html#Statelessness">stateless</a> |
| * function that accepts two partial result containers |
| * and merges them, which must be compatible with the |
| * accumulator function. The combiner function must fold |
| * the elements from the second result container into the |
| * first result container. |
| * @return the result of the reduction |
| * @see Stream#collect(Supplier, BiConsumer, BiConsumer) |
| */ |
| <R> R collect(Supplier<R> supplier, |
| ObjDoubleConsumer<R> accumulator, |
| BiConsumer<R, R> combiner); |
| |
| /** |
| * Returns the sum of elements in this stream. |
| * |
| * Summation is a special case of a <a |
| * href="package-summary.html#Reduction">reduction</a>. If |
| * floating-point summation were exact, this method would be |
| * equivalent to: |
| * |
| * <pre>{@code |
| * return reduce(0, Double::sum); |
| * }</pre> |
| * |
| * However, since floating-point summation is not exact, the above |
| * code is not necessarily equivalent to the summation computation |
| * done by this method. |
| * |
| * <p>The value of a floating-point sum is a function both |
| * of the input values as well as the order of addition |
| * operations. The order of addition operations of this method is |
| * intentionally not defined to allow for implementation |
| * flexibility to improve the speed and accuracy of the computed |
| * result. |
| * |
| * In particular, this method may be implemented using compensated |
| * summation or other technique to reduce the error bound in the |
| * numerical sum compared to a simple summation of {@code double} |
| * values. |
| * |
| * Because of the unspecified order of operations and the |
| * possibility of using differing summation schemes, the output of |
| * this method may vary on the same input elements. |
| * |
| * <p>Various conditions can result in a non-finite sum being |
| * computed. This can occur even if the all the elements |
| * being summed are finite. If any element is non-finite, |
| * the sum will be non-finite: |
| * |
| * <ul> |
| * |
| * <li>If any element is a NaN, then the final sum will be |
| * NaN. |
| * |
| * <li>If the elements contain one or more infinities, the |
| * sum will be infinite or NaN. |
| * |
| * <ul> |
| * |
| * <li>If the elements contain infinities of opposite sign, |
| * the sum will be NaN. |
| * |
| * <li>If the elements contain infinities of one sign and |
| * an intermediate sum overflows to an infinity of the opposite |
| * sign, the sum may be NaN. |
| * |
| * </ul> |
| * |
| * </ul> |
| * |
| * It is possible for intermediate sums of finite values to |
| * overflow into opposite-signed infinities; if that occurs, the |
| * final sum will be NaN even if the elements are all |
| * finite. |
| * |
| * If all the elements are zero, the sign of zero is |
| * <em>not</em> guaranteed to be preserved in the final sum. |
| * |
| * <p>This is a <a href="package-summary.html#StreamOps">terminal |
| * operation</a>. |
| * |
| * @apiNote Elements sorted by increasing absolute magnitude tend |
| * to yield more accurate results. |
| * |
| * @return the sum of elements in this stream |
| */ |
| double sum(); |
| |
| /** |
| * Returns an {@code OptionalDouble} describing the minimum element of this |
| * stream, or an empty OptionalDouble if this stream is empty. The minimum |
| * element will be {@code Double.NaN} if any stream element was NaN. Unlike |
| * the numerical comparison operators, this method considers negative zero |
| * to be strictly smaller than positive zero. This is a special case of a |
| * <a href="package-summary.html#Reduction">reduction</a> and is |
| * equivalent to: |
| * <pre>{@code |
| * return reduce(Double::min); |
| * }</pre> |
| * |
| * <p>This is a <a href="package-summary.html#StreamOps">terminal |
| * operation</a>. |
| * |
| * @return an {@code OptionalDouble} containing the minimum element of this |
| * stream, or an empty optional if the stream is empty |
| */ |
| OptionalDouble min(); |
| |
| /** |
| * Returns an {@code OptionalDouble} describing the maximum element of this |
| * stream, or an empty OptionalDouble if this stream is empty. The maximum |
| * element will be {@code Double.NaN} if any stream element was NaN. Unlike |
| * the numerical comparison operators, this method considers negative zero |
| * to be strictly smaller than positive zero. This is a |
| * special case of a |
| * <a href="package-summary.html#Reduction">reduction</a> and is |
| * equivalent to: |
| * <pre>{@code |
| * return reduce(Double::max); |
| * }</pre> |
| * |
| * <p>This is a <a href="package-summary.html#StreamOps">terminal |
| * operation</a>. |
| * |
| * @return an {@code OptionalDouble} containing the maximum element of this |
| * stream, or an empty optional if the stream is empty |
| */ |
| OptionalDouble max(); |
| |
| /** |
| * Returns the count of elements in this stream. This is a special case of |
| * a <a href="package-summary.html#Reduction">reduction</a> and is |
| * equivalent to: |
| * <pre>{@code |
| * return mapToLong(e -> 1L).sum(); |
| * }</pre> |
| * |
| * <p>This is a <a href="package-summary.html#StreamOps">terminal operation</a>. |
| * |
| * @apiNote |
| * An implementation may choose to not execute the stream pipeline (either |
| * sequentially or in parallel) if it is capable of computing the count |
| * directly from the stream source. In such cases no source elements will |
| * be traversed and no intermediate operations will be evaluated. |
| * Behavioral parameters with side-effects, which are strongly discouraged |
| * except for harmless cases such as debugging, may be affected. For |
| * example, consider the following stream: |
| * <pre>{@code |
| * DoubleStream s = DoubleStream.of(1, 2, 3, 4); |
| * long count = s.peek(System.out::println).count(); |
| * }</pre> |
| * The number of elements covered by the stream source is known and the |
| * intermediate operation, {@code peek}, does not inject into or remove |
| * elements from the stream (as may be the case for {@code flatMap} or |
| * {@code filter} operations). Thus the count is 4 and there is no need to |
| * execute the pipeline and, as a side-effect, print out the elements. |
| * |
| * @return the count of elements in this stream |
| */ |
| long count(); |
| |
| /** |
| * Returns an {@code OptionalDouble} describing the arithmetic |
| * mean of elements of this stream, or an empty optional if this |
| * stream is empty. |
| * |
| * <p>The computed average can vary numerically and have the |
| * special case behavior as computing the sum; see {@link #sum} |
| * for details. |
| * |
| * <p>The average is a special case of a <a |
| * href="package-summary.html#Reduction">reduction</a>. |
| * |
| * <p>This is a <a href="package-summary.html#StreamOps">terminal |
| * operation</a>. |
| * |
| * @apiNote Elements sorted by increasing absolute magnitude tend |
| * to yield more accurate results. |
| * |
| * @return an {@code OptionalDouble} containing the average element of this |
| * stream, or an empty optional if the stream is empty |
| */ |
| OptionalDouble average(); |
| |
| /** |
| * Returns a {@code DoubleSummaryStatistics} describing various summary data |
| * about the elements of this stream. This is a special |
| * case of a <a href="package-summary.html#Reduction">reduction</a>. |
| * |
| * <p>This is a <a href="package-summary.html#StreamOps">terminal |
| * operation</a>. |
| * |
| * @return a {@code DoubleSummaryStatistics} describing various summary data |
| * about the elements of this stream |
| */ |
| DoubleSummaryStatistics summaryStatistics(); |
| |
| /** |
| * Returns whether any elements of this stream match the provided |
| * predicate. May not evaluate the predicate on all elements if not |
| * necessary for determining the result. If the stream is empty then |
| * {@code false} is returned and the predicate is not evaluated. |
| * |
| * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting |
| * terminal operation</a>. |
| * |
| * @apiNote |
| * This method evaluates the <em>existential quantification</em> of the |
| * predicate over the elements of the stream (for some x P(x)). |
| * |
| * @param predicate a <a href="package-summary.html#NonInterference">non-interfering</a>, |
| * <a href="package-summary.html#Statelessness">stateless</a> |
| * predicate to apply to elements of this stream |
| * @return {@code true} if any elements of the stream match the provided |
| * predicate, otherwise {@code false} |
| */ |
| boolean anyMatch(DoublePredicate predicate); |
| |
| /** |
| * Returns whether all elements of this stream match the provided predicate. |
| * May not evaluate the predicate on all elements if not necessary for |
| * determining the result. If the stream is empty then {@code true} is |
| * returned and the predicate is not evaluated. |
| * |
| * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting |
| * terminal operation</a>. |
| * |
| * @apiNote |
| * This method evaluates the <em>universal quantification</em> of the |
| * predicate over the elements of the stream (for all x P(x)). If the |
| * stream is empty, the quantification is said to be <em>vacuously |
| * satisfied</em> and is always {@code true} (regardless of P(x)). |
| * |
| * @param predicate a <a href="package-summary.html#NonInterference">non-interfering</a>, |
| * <a href="package-summary.html#Statelessness">stateless</a> |
| * predicate to apply to elements of this stream |
| * @return {@code true} if either all elements of the stream match the |
| * provided predicate or the stream is empty, otherwise {@code false} |
| */ |
| boolean allMatch(DoublePredicate predicate); |
| |
| /** |
| * Returns whether no elements of this stream match the provided predicate. |
| * May not evaluate the predicate on all elements if not necessary for |
| * determining the result. If the stream is empty then {@code true} is |
| * returned and the predicate is not evaluated. |
| * |
| * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting |
| * terminal operation</a>. |
| * |
| * @apiNote |
| * This method evaluates the <em>universal quantification</em> of the |
| * negated predicate over the elements of the stream (for all x ~P(x)). If |
| * the stream is empty, the quantification is said to be vacuously satisfied |
| * and is always {@code true}, regardless of P(x). |
| * |
| * @param predicate a <a href="package-summary.html#NonInterference">non-interfering</a>, |
| * <a href="package-summary.html#Statelessness">stateless</a> |
| * predicate to apply to elements of this stream |
| * @return {@code true} if either no elements of the stream match the |
| * provided predicate or the stream is empty, otherwise {@code false} |
| */ |
| boolean noneMatch(DoublePredicate predicate); |
| |
| /** |
| * Returns an {@link OptionalDouble} describing the first element of this |
| * stream, or an empty {@code OptionalDouble} if the stream is empty. If |
| * the stream has no encounter order, then any element may be returned. |
| * |
| * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting |
| * terminal operation</a>. |
| * |
| * @return an {@code OptionalDouble} describing the first element of this |
| * stream, or an empty {@code OptionalDouble} if the stream is empty |
| */ |
| OptionalDouble findFirst(); |
| |
| /** |
| * Returns an {@link OptionalDouble} describing some element of the stream, |
| * or an empty {@code OptionalDouble} if the stream is empty. |
| * |
| * <p>This is a <a href="package-summary.html#StreamOps">short-circuiting |
| * terminal operation</a>. |
| * |
| * <p>The behavior of this operation is explicitly nondeterministic; it is |
| * free to select any element in the stream. This is to allow for maximal |
| * performance in parallel operations; the cost is that multiple invocations |
| * on the same source may not return the same result. (If a stable result |
| * is desired, use {@link #findFirst()} instead.) |
| * |
| * @return an {@code OptionalDouble} describing some element of this stream, |
| * or an empty {@code OptionalDouble} if the stream is empty |
| * @see #findFirst() |
| */ |
| OptionalDouble findAny(); |
| |
| /** |
| * Returns a {@code Stream} consisting of the elements of this stream, |
| * boxed to {@code Double}. |
| * |
| * <p>This is an <a href="package-summary.html#StreamOps">intermediate |
| * operation</a>. |
| * |
| * @return a {@code Stream} consistent of the elements of this stream, |
| * each boxed to a {@code Double} |
| */ |
| Stream<Double> boxed(); |
| |
| @Override |
| DoubleStream sequential(); |
| |
| @Override |
| DoubleStream parallel(); |
| |
| @Override |
| PrimitiveIterator.OfDouble iterator(); |
| |
| @Override |
| Spliterator.OfDouble spliterator(); |
| |
| |
| // Static factories |
| |
| /** |
| * Returns a builder for a {@code DoubleStream}. |
| * |
| * @return a stream builder |
| */ |
| public static Builder builder() { |
| return new Streams.DoubleStreamBuilderImpl(); |
| } |
| |
| /** |
| * Returns an empty sequential {@code DoubleStream}. |
| * |
| * @return an empty sequential stream |
| */ |
| public static DoubleStream empty() { |
| return StreamSupport.doubleStream(Spliterators.emptyDoubleSpliterator(), false); |
| } |
| |
| /** |
| * Returns a sequential {@code DoubleStream} containing a single element. |
| * |
| * @param t the single element |
| * @return a singleton sequential stream |
| */ |
| public static DoubleStream of(double t) { |
| return StreamSupport.doubleStream(new Streams.DoubleStreamBuilderImpl(t), false); |
| } |
| |
| /** |
| * Returns a sequential ordered stream whose elements are the specified values. |
| * |
| * @param values the elements of the new stream |
| * @return the new stream |
| */ |
| public static DoubleStream of(double... values) { |
| return Arrays.stream(values); |
| } |
| |
| /** |
| * Returns an infinite sequential ordered {@code DoubleStream} produced by iterative |
| * application of a function {@code f} to an initial element {@code seed}, |
| * producing a {@code Stream} consisting of {@code seed}, {@code f(seed)}, |
| * {@code f(f(seed))}, etc. |
| * |
| * <p>The first element (position {@code 0}) in the {@code DoubleStream} |
| * will be the provided {@code seed}. For {@code n > 0}, the element at |
| * position {@code n}, will be the result of applying the function {@code f} |
| * to the element at position {@code n - 1}. |
| * |
| * <p>The action of applying {@code f} for one element |
| * <a href="../concurrent/package-summary.html#MemoryVisibility"><i>happens-before</i></a> |
| * the action of applying {@code f} for subsequent elements. For any given |
| * element the action may be performed in whatever thread the library |
| * chooses. |
| * |
| * @param seed the initial element |
| * @param f a function to be applied to the previous element to produce |
| * a new element |
| * @return a new sequential {@code DoubleStream} |
| */ |
| public static DoubleStream iterate(final double seed, final DoubleUnaryOperator f) { |
| Objects.requireNonNull(f); |
| Spliterator.OfDouble spliterator = new Spliterators.AbstractDoubleSpliterator(Long.MAX_VALUE, |
| Spliterator.ORDERED | Spliterator.IMMUTABLE | Spliterator.NONNULL) { |
| double prev; |
| boolean started; |
| |
| @Override |
| public boolean tryAdvance(DoubleConsumer action) { |
| Objects.requireNonNull(action); |
| double t; |
| if (started) |
| t = f.applyAsDouble(prev); |
| else { |
| t = seed; |
| started = true; |
| } |
| action.accept(prev = t); |
| return true; |
| } |
| }; |
| return StreamSupport.doubleStream(spliterator, false); |
| } |
| |
| /** |
| * Returns a sequential ordered {@code DoubleStream} produced by iterative |
| * application of the given {@code next} function to an initial element, |
| * conditioned on satisfying the given {@code hasNext} predicate. The |
| * stream terminates as soon as the {@code hasNext} predicate returns false. |
| * |
| * <p>{@code DoubleStream.iterate} should produce the same sequence of elements as |
| * produced by the corresponding for-loop: |
| * <pre>{@code |
| * for (double index=seed; hasNext.test(index); index = next.applyAsDouble(index)) { |
| * ... |
| * } |
| * }</pre> |
| * |
| * <p>The resulting sequence may be empty if the {@code hasNext} predicate |
| * does not hold on the seed value. Otherwise the first element will be the |
| * supplied {@code seed} value, the next element (if present) will be the |
| * result of applying the {@code next} function to the {@code seed} value, |
| * and so on iteratively until the {@code hasNext} predicate indicates that |
| * the stream should terminate. |
| * |
| * <p>The action of applying the {@code hasNext} predicate to an element |
| * <a href="../concurrent/package-summary.html#MemoryVisibility"><i>happens-before</i></a> |
| * the action of applying the {@code next} function to that element. The |
| * action of applying the {@code next} function for one element |
| * <i>happens-before</i> the action of applying the {@code hasNext} |
| * predicate for subsequent elements. For any given element an action may |
| * be performed in whatever thread the library chooses. |
| * |
| * @param seed the initial element |
| * @param hasNext a predicate to apply to elements to determine when the |
| * stream must terminate. |
| * @param next a function to be applied to the previous element to produce |
| * a new element |
| * @return a new sequential {@code DoubleStream} |
| * @since 9 |
| */ |
| public static DoubleStream iterate(double seed, DoublePredicate hasNext, DoubleUnaryOperator next) { |
| Objects.requireNonNull(next); |
| Objects.requireNonNull(hasNext); |
| Spliterator.OfDouble spliterator = new Spliterators.AbstractDoubleSpliterator(Long.MAX_VALUE, |
| Spliterator.ORDERED | Spliterator.IMMUTABLE | Spliterator.NONNULL) { |
| double prev; |
| boolean started, finished; |
| |
| @Override |
| public boolean tryAdvance(DoubleConsumer action) { |
| Objects.requireNonNull(action); |
| if (finished) |
| return false; |
| double t; |
| if (started) |
| t = next.applyAsDouble(prev); |
| else { |
| t = seed; |
| started = true; |
| } |
| if (!hasNext.test(t)) { |
| finished = true; |
| return false; |
| } |
| action.accept(prev = t); |
| return true; |
| } |
| |
| @Override |
| public void forEachRemaining(DoubleConsumer action) { |
| Objects.requireNonNull(action); |
| if (finished) |
| return; |
| finished = true; |
| double t = started ? next.applyAsDouble(prev) : seed; |
| while (hasNext.test(t)) { |
| action.accept(t); |
| t = next.applyAsDouble(t); |
| } |
| } |
| }; |
| return StreamSupport.doubleStream(spliterator, false); |
| } |
| |
| /** |
| * Returns an infinite sequential unordered stream where each element is |
| * generated by the provided {@code DoubleSupplier}. This is suitable for |
| * generating constant streams, streams of random elements, etc. |
| * |
| * @param s the {@code DoubleSupplier} for generated elements |
| * @return a new infinite sequential unordered {@code DoubleStream} |
| */ |
| public static DoubleStream generate(DoubleSupplier s) { |
| Objects.requireNonNull(s); |
| return StreamSupport.doubleStream( |
| new StreamSpliterators.InfiniteSupplyingSpliterator.OfDouble(Long.MAX_VALUE, s), false); |
| } |
| |
| /** |
| * Creates a lazily concatenated stream whose elements are all the |
| * elements of the first stream followed by all the elements of the |
| * second stream. The resulting stream is ordered if both |
| * of the input streams are ordered, and parallel if either of the input |
| * streams is parallel. When the resulting stream is closed, the close |
| * handlers for both input streams are invoked. |
| * |
| * <p>This method operates on the two input streams and binds each stream |
| * to its source. As a result subsequent modifications to an input stream |
| * source may not be reflected in the concatenated stream result. |
| * |
| * @implNote |
| * Use caution when constructing streams from repeated concatenation. |
| * Accessing an element of a deeply concatenated stream can result in deep |
| * call chains, or even {@code StackOverflowError}. |
| * |
| * @apiNote |
| * To preserve optimization opportunities this method binds each stream to |
| * its source and accepts only two streams as parameters. For example, the |
| * exact size of the concatenated stream source can be computed if the exact |
| * size of each input stream source is known. |
| * To concatenate more streams without binding, or without nested calls to |
| * this method, try creating a stream of streams and flat-mapping with the |
| * identity function, for example: |
| * <pre>{@code |
| * DoubleStream concat = Stream.of(s1, s2, s3, s4).flatMapToDouble(s -> s); |
| * }</pre> |
| * |
| * @param a the first stream |
| * @param b the second stream |
| * @return the concatenation of the two input streams |
| */ |
| public static DoubleStream concat(DoubleStream a, DoubleStream b) { |
| Objects.requireNonNull(a); |
| Objects.requireNonNull(b); |
| |
| Spliterator.OfDouble split = new Streams.ConcatSpliterator.OfDouble( |
| a.spliterator(), b.spliterator()); |
| DoubleStream stream = StreamSupport.doubleStream(split, a.isParallel() || b.isParallel()); |
| return stream.onClose(Streams.composedClose(a, b)); |
| } |
| |
| /** |
| * A mutable builder for a {@code DoubleStream}. |
| * |
| * <p>A stream builder has a lifecycle, which starts in a building |
| * phase, during which elements can be added, and then transitions to a built |
| * phase, after which elements may not be added. The built phase |
| * begins when the {@link #build()} method is called, which creates an |
| * ordered stream whose elements are the elements that were added to the |
| * stream builder, in the order they were added. |
| * |
| * @see DoubleStream#builder() |
| * @since 1.8 |
| */ |
| public interface Builder extends DoubleConsumer { |
| |
| /** |
| * Adds an element to the stream being built. |
| * |
| * @throws IllegalStateException if the builder has already transitioned |
| * to the built state |
| */ |
| @Override |
| void accept(double t); |
| |
| /** |
| * Adds an element to the stream being built. |
| * |
| * @implSpec |
| * The default implementation behaves as if: |
| * <pre>{@code |
| * accept(t) |
| * return this; |
| * }</pre> |
| * |
| * @param t the element to add |
| * @return {@code this} builder |
| * @throws IllegalStateException if the builder has already transitioned |
| * to the built state |
| */ |
| default Builder add(double t) { |
| accept(t); |
| return this; |
| } |
| |
| /** |
| * Builds the stream, transitioning this builder to the built state. |
| * An {@code IllegalStateException} is thrown if there are further |
| * attempts to operate on the builder after it has entered the built |
| * state. |
| * |
| * @return the built stream |
| * @throws IllegalStateException if the builder has already transitioned |
| * to the built state |
| */ |
| DoubleStream build(); |
| } |
| |
| /** |
| * Represents an operation that accepts a {@code double}-valued argument |
| * and a DoubleConsumer, and returns no result. This functional interface is |
| * used by {@link DoubleStream#mapMulti(DoubleMapMultiConsumer) DoubleStream.mapMulti} |
| * to replace a double value with zero or more double values. |
| * |
| * <p>This is a <a href="../function/package-summary.html">functional interface</a> |
| * whose functional method is {@link #accept(double, DoubleConsumer)}. |
| * |
| * @see DoubleStream#mapMulti(DoubleMapMultiConsumer) |
| * |
| * @since 16 |
| */ |
| @FunctionalInterface |
| interface DoubleMapMultiConsumer { |
| |
| /** |
| * Replaces the given {@code value} with zero or more values by feeding the mapped |
| * values to the {@code dc} consumer. |
| * |
| * @param value the double value coming from upstream |
| * @param dc a {@code DoubleConsumer} accepting the mapped values |
| */ |
| void accept(double value, DoubleConsumer dc); |
| } |
| } |
