1 /*
   2  * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 package java.util.stream;
  26 
  27 import java.util.Iterator;
  28 import java.util.Spliterator;
  29 
  30 /**
  31  * Base interface for stream types such as {@link Stream}, {@link IntStream},
  32  * etc.  Contains methods common to all stream types.  Many of these methods
  33  * are implemented by {@link AbstractPipeline}, even though
  34  * {@code AbstractPipeline} does not directly implement {@code BaseStream}.
  35  *
  36  * @param <T> type of stream elements
  37  * @param <S> type of stream implementing {@code BaseStream}
  38  * @since 1.8
  39  */
  40 interface BaseStream<T, S extends BaseStream<T, S>> {
  41     /**
  42      * Returns an iterator for the elements of this stream.
  43      *
  44      * <p>This is a <a href="package-summary.html#StreamOps">terminal
  45      * operation</a>.
  46      *
  47      * @return the element iterator for this stream
  48      */
  49     Iterator<T> iterator();
  50 
  51     /**
  52      * Returns a spliterator for the elements of this stream.
  53      *
  54      * <p>This is a <a href="package-summary.html#StreamOps">terminal
  55      * operation</a>.
  56      *
  57      * @return the element spliterator for this stream
  58      */
  59     Spliterator<T> spliterator();
  60 
  61     /**
  62      * Returns whether this stream, when executed, would execute in parallel
  63      * (assuming no further modification of the stream, such as appending
  64      * further intermediate operations or changing its parallelism).  Calling
  65      * this method after invoking an intermediate or terminal stream operation
  66      * method may yield unpredictable results.
  67      *
  68      * @return {@code true} if this stream would execute in parallel if executed
  69      * without further modification otherwise {@code false}
  70      */
  71     boolean isParallel();
  72 
  73     /**
  74      * Returns an equivalent stream that is sequential.  May return
  75      * itself, either because the stream was already sequential, or because
  76      * the underlying stream state was modified to be sequential.
  77      *
  78      * <p>This is an <a href="package-summary.html#StreamOps">intermediate
  79      * operation</a>.
  80      *
  81      * @return a sequential stream
  82      */
  83     S sequential();
  84 
  85     /**
  86      * Returns an equivalent stream that is parallel.  May return
  87      * itself, either because the stream was already parallel, or because
  88      * the underlying stream state was modified to be parallel.
  89      *
  90      * <p>This is an <a href="package-summary.html#StreamOps">intermediate
  91      * operation</a>.
  92      *
  93      * @return a parallel stream
  94      */
  95     S parallel();
  96 
  97     /**
  98      * Returns an equivalent stream that is
  99      * <a href="package-summary.html#Ordering">unordered</a>.  May return
 100      * itself if the stream was already unordered.
 101      *
 102      * <p>This is an <a href="package-summary.html#StreamOps">intermediate
 103      * operation</a>.
 104      *
 105      * @return an unordered stream
 106      */
 107     S unordered();
 108 }