Java tutorial
/* * Copyright (c) 2012, 2013, 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.Objects; import java.util.Spliterator; import java.util.function.Supplier; /** * Low-level utility methods for creating and manipulating streams. * * <p>This class is mostly for library writers presenting stream views * of data structures; most static stream methods intended for end users are in * the various {@code Stream} classes. * * @since 1.8 */ public final class StreamSupport { // Suppresses default constructor, ensuring non-instantiability. private StreamSupport() { } /** * Creates a new sequential or parallel {@code Stream} from a * {@code Spliterator}. * * <p>The spliterator is only traversed, split, or queried for estimated * size after the terminal operation of the stream pipeline commences. * * <p>It is strongly recommended the spliterator report a characteristic of * {@code IMMUTABLE} or {@code CONCURRENT}, or be * <a href="../Spliterator.html#binding">late-binding</a>. Otherwise, * {@link #stream(java.util.function.Supplier, int, boolean)} should be used * to reduce the scope of potential interference with the source. See * <a href="package-summary.html#NonInterference">Non-Interference</a> for * more details. * * @param <T> the type of stream elements * @param spliterator a {@code Spliterator} describing the stream elements * @param parallel if {@code true} then the returned stream is a parallel * stream; if {@code false} the returned stream is a sequential * stream. * @return a new sequential or parallel {@code Stream} */ public static <T> Stream<T> stream(Spliterator<T> spliterator, boolean parallel) { Objects.requireNonNull(spliterator); return new ReferencePipeline.Head<>(spliterator, StreamOpFlag.fromCharacteristics(spliterator), parallel); } /** * Creates a new sequential or parallel {@code Stream} from a * {@code Supplier} of {@code Spliterator}. * * <p>The {@link Supplier#get()} method will be invoked on the supplier no * more than once, and only after the terminal operation of the stream pipeline * commences. * * <p>For spliterators that report a characteristic of {@code IMMUTABLE} * or {@code CONCURRENT}, or that are * <a href="../Spliterator.html#binding">late-binding</a>, it is likely * more efficient to use {@link #stream(java.util.Spliterator, boolean)} * instead. * <p>The use of a {@code Supplier} in this form provides a level of * indirection that reduces the scope of potential interference with the * source. Since the supplier is only invoked after the terminal operation * commences, any modifications to the source up to the start of the * terminal operation are reflected in the stream result. See * <a href="package-summary.html#NonInterference">Non-Interference</a> for * more details. * * @param <T> the type of stream elements * @param supplier a {@code Supplier} of a {@code Spliterator} * @param characteristics Spliterator characteristics of the supplied * {@code Spliterator}. The characteristics must be equal to * {@code supplier.get().characteristics()}, otherwise undefined * behavior may occur when terminal operation commences. * @param parallel if {@code true} then the returned stream is a parallel * stream; if {@code false} the returned stream is a sequential * stream. * @return a new sequential or parallel {@code Stream} * @see #stream(java.util.Spliterator, boolean) */ public static <T> Stream<T> stream(Supplier<? extends Spliterator<T>> supplier, int characteristics, boolean parallel) { Objects.requireNonNull(supplier); return new ReferencePipeline.Head<>(supplier, StreamOpFlag.fromCharacteristics(characteristics), parallel); } /** * Creates a new sequential or parallel {@code IntStream} from a * {@code Spliterator.OfInt}. * * <p>The spliterator is only traversed, split, or queried for estimated size * after the terminal operation of the stream pipeline commences. * * <p>It is strongly recommended the spliterator report a characteristic of * {@code IMMUTABLE} or {@code CONCURRENT}, or be * <a href="../Spliterator.html#binding">late-binding</a>. Otherwise, * {@link #intStream(java.util.function.Supplier, int, boolean)} should be * used to reduce the scope of potential interference with the source. See * <a href="package-summary.html#NonInterference">Non-Interference</a> for * more details. * * @param spliterator a {@code Spliterator.OfInt} describing the stream elements * @param parallel if {@code true} then the returned stream is a parallel * stream; if {@code false} the returned stream is a sequential * stream. * @return a new sequential or parallel {@code IntStream} */ public static IntStream intStream(Spliterator.OfInt spliterator, boolean parallel) { return new IntPipeline.Head<>(spliterator, StreamOpFlag.fromCharacteristics(spliterator), parallel); } /** * Creates a new sequential or parallel {@code IntStream} from a * {@code Supplier} of {@code Spliterator.OfInt}. * * <p>The {@link Supplier#get()} method will be invoked on the supplier no * more than once, and only after the terminal operation of the stream pipeline * commences. * * <p>For spliterators that report a characteristic of {@code IMMUTABLE} * or {@code CONCURRENT}, or that are * <a href="../Spliterator.html#binding">late-binding</a>, it is likely * more efficient to use {@link #intStream(java.util.Spliterator.OfInt, boolean)} * instead. * <p>The use of a {@code Supplier} in this form provides a level of * indirection that reduces the scope of potential interference with the * source. Since the supplier is only invoked after the terminal operation * commences, any modifications to the source up to the start of the * terminal operation are reflected in the stream result. See * <a href="package-summary.html#NonInterference">Non-Interference</a> for * more details. * * @param supplier a {@code Supplier} of a {@code Spliterator.OfInt} * @param characteristics Spliterator characteristics of the supplied * {@code Spliterator.OfInt}. The characteristics must be equal to * {@code supplier.get().characteristics()}, otherwise undefined * behavior may occur when terminal operation commences. * @param parallel if {@code true} then the returned stream is a parallel * stream; if {@code false} the returned stream is a sequential * stream. * @return a new sequential or parallel {@code IntStream} * @see #intStream(java.util.Spliterator.OfInt, boolean) */ public static IntStream intStream(Supplier<? extends Spliterator.OfInt> supplier, int characteristics, boolean parallel) { return new IntPipeline.Head<>(supplier, StreamOpFlag.fromCharacteristics(characteristics), parallel); } /** * Creates a new sequential or parallel {@code LongStream} from a * {@code Spliterator.OfLong}. * * <p>The spliterator is only traversed, split, or queried for estimated * size after the terminal operation of the stream pipeline commences. * * <p>It is strongly recommended the spliterator report a characteristic of * {@code IMMUTABLE} or {@code CONCURRENT}, or be * <a href="../Spliterator.html#binding">late-binding</a>. Otherwise, * {@link #longStream(java.util.function.Supplier, int, boolean)} should be * used to reduce the scope of potential interference with the source. See * <a href="package-summary.html#NonInterference">Non-Interference</a> for * more details. * * @param spliterator a {@code Spliterator.OfLong} describing the stream elements * @param parallel if {@code true} then the returned stream is a parallel * stream; if {@code false} the returned stream is a sequential * stream. * @return a new sequential or parallel {@code LongStream} */ public static LongStream longStream(Spliterator.OfLong spliterator, boolean parallel) { return new LongPipeline.Head<>(spliterator, StreamOpFlag.fromCharacteristics(spliterator), parallel); } /** * Creates a new sequential or parallel {@code LongStream} from a * {@code Supplier} of {@code Spliterator.OfLong}. * * <p>The {@link Supplier#get()} method will be invoked on the supplier no * more than once, and only after the terminal operation of the stream pipeline * commences. * * <p>For spliterators that report a characteristic of {@code IMMUTABLE} * or {@code CONCURRENT}, or that are * <a href="../Spliterator.html#binding">late-binding</a>, it is likely * more efficient to use {@link #longStream(java.util.Spliterator.OfLong, boolean)} * instead. * <p>The use of a {@code Supplier} in this form provides a level of * indirection that reduces the scope of potential interference with the * source. Since the supplier is only invoked after the terminal operation * commences, any modifications to the source up to the start of the * terminal operation are reflected in the stream result. See * <a href="package-summary.html#NonInterference">Non-Interference</a> for * more details. * * @param supplier a {@code Supplier} of a {@code Spliterator.OfLong} * @param characteristics Spliterator characteristics of the supplied * {@code Spliterator.OfLong}. The characteristics must be equal to * {@code supplier.get().characteristics()}, otherwise undefined * behavior may occur when terminal operation commences. * @param parallel if {@code true} then the returned stream is a parallel * stream; if {@code false} the returned stream is a sequential * stream. * @return a new sequential or parallel {@code LongStream} * @see #longStream(java.util.Spliterator.OfLong, boolean) */ public static LongStream longStream(Supplier<? extends Spliterator.OfLong> supplier, int characteristics, boolean parallel) { return new LongPipeline.Head<>(supplier, StreamOpFlag.fromCharacteristics(characteristics), parallel); } /** * Creates a new sequential or parallel {@code DoubleStream} from a * {@code Spliterator.OfDouble}. * * <p>The spliterator is only traversed, split, or queried for estimated size * after the terminal operation of the stream pipeline commences. * * <p>It is strongly recommended the spliterator report a characteristic of * {@code IMMUTABLE} or {@code CONCURRENT}, or be * <a href="../Spliterator.html#binding">late-binding</a>. Otherwise, * {@link #doubleStream(java.util.function.Supplier, int, boolean)} should * be used to reduce the scope of potential interference with the source. See * <a href="package-summary.html#NonInterference">Non-Interference</a> for * more details. * * @param spliterator A {@code Spliterator.OfDouble} describing the stream elements * @param parallel if {@code true} then the returned stream is a parallel * stream; if {@code false} the returned stream is a sequential * stream. * @return a new sequential or parallel {@code DoubleStream} */ public static DoubleStream doubleStream(Spliterator.OfDouble spliterator, boolean parallel) { return new DoublePipeline.Head<>(spliterator, StreamOpFlag.fromCharacteristics(spliterator), parallel); } /** * Creates a new sequential or parallel {@code DoubleStream} from a * {@code Supplier} of {@code Spliterator.OfDouble}. * * <p>The {@link Supplier#get()} method will be invoked on the supplier no * more than once, and only after the terminal operation of the stream pipeline * commences. * * <p>For spliterators that report a characteristic of {@code IMMUTABLE} * or {@code CONCURRENT}, or that are * <a href="../Spliterator.html#binding">late-binding</a>, it is likely * more efficient to use {@link #doubleStream(java.util.Spliterator.OfDouble, boolean)} * instead. * <p>The use of a {@code Supplier} in this form provides a level of * indirection that reduces the scope of potential interference with the * source. Since the supplier is only invoked after the terminal operation * commences, any modifications to the source up to the start of the * terminal operation are reflected in the stream result. See * <a href="package-summary.html#NonInterference">Non-Interference</a> for * more details. * * @param supplier A {@code Supplier} of a {@code Spliterator.OfDouble} * @param characteristics Spliterator characteristics of the supplied * {@code Spliterator.OfDouble}. The characteristics must be equal to * {@code supplier.get().characteristics()}, otherwise undefined * behavior may occur when terminal operation commences. * @param parallel if {@code true} then the returned stream is a parallel * stream; if {@code false} the returned stream is a sequential * stream. * @return a new sequential or parallel {@code DoubleStream} * @see #doubleStream(java.util.Spliterator.OfDouble, boolean) */ public static DoubleStream doubleStream(Supplier<? extends Spliterator.OfDouble> supplier, int characteristics, boolean parallel) { return new DoublePipeline.Head<>(supplier, StreamOpFlag.fromCharacteristics(characteristics), parallel); } }