001 /* Comparable.java -- Interface for comparaing objects to obtain an ordering 002 Copyright (C) 1998, 1999, 2001, 2002, 2004, 2005 Free Software Foundation, Inc. 003 004 This file is part of GNU Classpath. 005 006 GNU Classpath is free software; you can redistribute it and/or modify 007 it under the terms of the GNU General Public License as published by 008 the Free Software Foundation; either version 2, or (at your option) 009 any later version. 010 011 GNU Classpath is distributed in the hope that it will be useful, but 012 WITHOUT ANY WARRANTY; without even the implied warranty of 013 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 014 General Public License for more details. 015 016 You should have received a copy of the GNU General Public License 017 along with GNU Classpath; see the file COPYING. If not, write to the 018 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 019 02110-1301 USA. 020 021 Linking this library statically or dynamically with other modules is 022 making a combined work based on this library. Thus, the terms and 023 conditions of the GNU General Public License cover the whole 024 combination. 025 026 As a special exception, the copyright holders of this library give you 027 permission to link this library with independent modules to produce an 028 executable, regardless of the license terms of these independent 029 modules, and to copy and distribute the resulting executable under 030 terms of your choice, provided that you also meet, for each linked 031 independent module, the terms and conditions of the license of that 032 module. An independent module is a module which is not derived from 033 or based on this library. If you modify this library, you may extend 034 this exception to your version of the library, but you are not 035 obligated to do so. If you do not wish to do so, delete this 036 exception statement from your version. */ 037 038 039 package java.lang; 040 041 /** 042 * Interface for objects that can be ordering among other objects. The 043 * ordering can be <em>total</em>, such that two objects only compare equal 044 * if they are also equal by the equals method, or <em>partial</em> such 045 * that this is not necessarily true. For example, a case-sensitive 046 * dictionary order comparison of Strings is total, but if it is 047 * case-insensitive it is partial, because "abc" and "ABC" compare as 048 * equal even though "abc".equals("ABC") returns false. However, if you use 049 * a partial ordering, it is a good idea to document your class as 050 * "inconsistent with equals", because the behavior of your class in a 051 * SortedMap will be different than in a HashMap. 052 * 053 * <p>Lists, arrays, and sets of objects that implement this interface can 054 * be sorted automatically, without the need for an explicit 055 * {@link java.util.Comparator}. Note that <code>e1.compareTo(null)</code> 056 * should throw an Exception; as should comparison between incompatible 057 * classes. 058 * 059 * @author Geoff Berry 060 * @author Warren Levy (warrenl@cygnus.com) 061 * @see java.util.Comparator 062 * @see java.util.Collections#sort(java.util.List) 063 * @see java.util.Arrays#sort(Object[]) 064 * @see java.util.SortedSet 065 * @see java.util.SortedMap 066 * @see java.util.TreeSet 067 * @see java.util.TreeMap 068 * @since 1.2 069 * @status updated to 1.5 070 */ 071 public interface Comparable<T> 072 { 073 /** 074 * Compares this object with another, and returns a numerical result based 075 * on the comparison. If the result is negative, this object sorts less 076 * than the other; if 0, the two are equal, and if positive, this object 077 * sorts greater than the other. To translate this into boolean, simply 078 * perform <code>o1.compareTo(o2) <em><op></em> 0</code>, where op 079 * is one of <, <=, =, !=, >, or >=. 080 * 081 * <p>You must make sure that the comparison is mutual, ie. 082 * <code>sgn(x.compareTo(y)) == -sgn(y.compareTo(x))</code> (where sgn() is 083 * defined as -1, 0, or 1 based on the sign). This includes throwing an 084 * exception in either direction if the two are not comparable; hence, 085 * <code>compareTo(null)</code> should always throw an Exception. 086 * 087 * <p>You should also ensure transitivity, in two forms: 088 * <code>x.compareTo(y) > 0 && y.compareTo(z) > 0</code> implies 089 * <code>x.compareTo(z) > 0</code>; and <code>x.compareTo(y) == 0</code> 090 * implies <code>x.compareTo(z) == y.compareTo(z)</code>. 091 * 092 * @param o the object to be compared 093 * @return an integer describing the comparison 094 * @throws NullPointerException if o is null 095 * @throws ClassCastException if o cannot be compared 096 */ 097 int compareTo(T o); 098 }