RandomAccess.java revision 309f9df28350e15445b9135e8b710fa2b34b5dc1 
1/*
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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
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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 *
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19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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24 */
25
26package java.util;
27
28/**
29 * Marker interface used by <tt>List</tt> 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 * <tt>ArrayList</tt>) can produce quadratic behavior when applied to
37 * sequential access lists (such as <tt>LinkedList</tt>).  Generic list
38 * algorithms are encouraged to check whether the given list is an
39 * <tt>instanceof</tt> 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 <tt>List</tt> implementations
46 * provide asymptotically linear access times if they get huge, but constant
47 * access times in practice.  Such a <tt>List</tt> implementation
48 * should generally implement this interface.  As a rule of thumb, a
49 * <tt>List</tt> 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}openjdk-redirect.html?v=8&path=/technotes/guides/collections/index.html">
63 * Java Collections Framework</a>.
64 *
65 * @since 1.4
66 */
67public interface RandomAccess {
68}
69