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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.

 *

 * 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

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 */

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 their data structures; most static stream methods for end users are in

 * {@link Streams}.

 *

 * <p>Unless otherwise stated, streams are created as sequential

 * streams.  A sequential stream can be transformed into a parallel stream by

 * calling the {@code parallel()} method on the created stream.

 *

 * @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#Non-Interference">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 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.

     * 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#Non-Interference">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()}.

     * @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#Non-Interference">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 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.

     * 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#Non-Interference">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()}

     * @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#Non-Interference">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 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.

     * 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#Non-Interference">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()}

     * @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#Non-Interference">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 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.

     * 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#Non-Interference">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()}

     * @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);

    }

}