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. 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 26 package 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 < 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}/../technotes/guides/collections/index.html"> 63 * Java Collections Framework</a>. 64 * 65 * @since 1.4 66 */ 67 public interface RandomAccess { 68 } 69