1 /*
   2  * Copyright (c) 2000, 2006, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   5  * This code is free software; you can redistribute it and/or modify it
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   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
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  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).
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  17  * You should have received a copy of the GNU General Public License version
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  25 
  26 package java.util;
  27 
  28 /**
  29  * Marker interface used by {@code List} implementations to indicate that
  30  * they support fast (generally constant time) random access.  The primary
  31  * purpose of this interface is to allow generic algorithms to alter their
  32  * behavior to provide good performance when applied to either random or
  33  * sequential access lists.
  34  *
  35  * <p>The best algorithms for manipulating random access lists (such as
  36  * {@code ArrayList}) can produce quadratic behavior when applied to
  37  * sequential access lists (such as {@code LinkedList}).  Generic list
  38  * algorithms are encouraged to check whether the given list is an
  39  * {@code instanceof} this interface before applying an algorithm that would
  40  * provide poor performance if it were applied to a sequential access list,
  41  * and to alter their behavior if necessary to guarantee acceptable
  42  * performance.
  43  *
  44  * <p>It is recognized that the distinction between random and sequential
  45  * access is often fuzzy.  For example, some {@code List} implementations
  46  * provide asymptotically linear access times if they get huge, but constant
  47  * access times in practice.  Such a {@code List} implementation
  48  * should generally implement this interface.  As a rule of thumb, a
  49  * {@code List} implementation should implement this interface if,
  50  * for typical instances of the class, this loop:
  51  * <pre>
  52  *     for (int i=0, n=list.size(); i &lt; n; i++)
  53  *         list.get(i);
  54  * </pre>
  55  * runs faster than this loop:
  56  * <pre>
  57  *     for (Iterator i=list.iterator(); i.hasNext(); )
  58  *         i.next();
  59  * </pre>
  60  *
  61  * <p>This interface is a member of the
  62  * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
  63  * Java Collections Framework</a>.
  64  *
  65  * @since 1.4
  66  */
  67 public interface RandomAccess {
  68 }