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 004This file is part of GNU Classpath. 005 006GNU Classpath is free software; you can redistribute it and/or modify 007it under the terms of the GNU General Public License as published by 008the Free Software Foundation; either version 2, or (at your option) 009any later version. 010 011GNU Classpath is distributed in the hope that it will be useful, but 012WITHOUT ANY WARRANTY; without even the implied warranty of 013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 014General Public License for more details. 015 016You should have received a copy of the GNU General Public License 017along with GNU Classpath; see the file COPYING. If not, write to the 018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 01902110-1301 USA. 020 021Linking this library statically or dynamically with other modules is 022making a combined work based on this library. Thus, the terms and 023conditions of the GNU General Public License cover the whole 024combination. 025 026As a special exception, the copyright holders of this library give you 027permission to link this library with independent modules to produce an 028executable, regardless of the license terms of these independent 029modules, and to copy and distribute the resulting executable under 030terms of your choice, provided that you also meet, for each linked 031independent module, the terms and conditions of the license of that 032module. An independent module is a module which is not derived from 033or based on this library. If you modify this library, you may extend 034this exception to your version of the library, but you are not 035obligated to do so. If you do not wish to do so, delete this 036exception statement from your version. */ 037 038 039package 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 */ 071public 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}