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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 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(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(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(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(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(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(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(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(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(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(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(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(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);
      }
  }
  