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1: /* Comparable.java -- Interface for comparaing objects to obtain an ordering 2: Copyright (C) 1998, 1999, 2001, 2002, 2004, 2005 Free Software Foundation, Inc. 3: 4: This file is part of GNU Classpath. 5: 6: GNU Classpath is free software; you can redistribute it and/or modify 7: it under the terms of the GNU General Public License as published by 8: the Free Software Foundation; either version 2, or (at your option) 9: any later version. 10: 11: GNU Classpath is distributed in the hope that it will be useful, but 12: WITHOUT ANY WARRANTY; without even the implied warranty of 13: MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 14: General Public License for more details. 15: 16: You should have received a copy of the GNU General Public License 17: along with GNU Classpath; see the file COPYING. If not, write to the 18: Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 19: 02110-1301 USA. 20: 21: Linking this library statically or dynamically with other modules is 22: making a combined work based on this library. Thus, the terms and 23: conditions of the GNU General Public License cover the whole 24: combination. 25: 26: As a special exception, the copyright holders of this library give you 27: permission to link this library with independent modules to produce an 28: executable, regardless of the license terms of these independent 29: modules, and to copy and distribute the resulting executable under 30: terms of your choice, provided that you also meet, for each linked 31: independent module, the terms and conditions of the license of that 32: module. An independent module is a module which is not derived from 33: or based on this library. If you modify this library, you may extend 34: this exception to your version of the library, but you are not 35: obligated to do so. If you do not wish to do so, delete this 36: exception statement from your version. */ 37: 38: 39: package java.lang; 40: 41: /** 42: * Interface for objects that can be ordering among other objects. The 43: * ordering can be <em>total</em>, such that two objects only compare equal 44: * if they are also equal by the equals method, or <em>partial</em> such 45: * that this is not necessarily true. For example, a case-sensitive 46: * dictionary order comparison of Strings is total, but if it is 47: * case-insensitive it is partial, because "abc" and "ABC" compare as 48: * equal even though "abc".equals("ABC") returns false. However, if you use 49: * a partial ordering, it is a good idea to document your class as 50: * "inconsistent with equals", because the behavior of your class in a 51: * SortedMap will be different than in a HashMap. 52: * 53: * <p>Lists, arrays, and sets of objects that implement this interface can 54: * be sorted automatically, without the need for an explicit 55: * {@link java.util.Comparator}. Note that <code>e1.compareTo(null)</code> 56: * should throw an Exception; as should comparison between incompatible 57: * classes. 58: * 59: * @author Geoff Berry 60: * @author Warren Levy (warrenl@cygnus.com) 61: * @see java.util.Comparator 62: * @see java.util.Collections#sort(java.util.List) 63: * @see java.util.Arrays#sort(Object[]) 64: * @see java.util.SortedSet 65: * @see java.util.SortedMap 66: * @see java.util.TreeSet 67: * @see java.util.TreeMap 68: * @since 1.2 69: * @status updated to 1.5 70: */ 71: public interface Comparable<T> 72: { 73: /** 74: * Compares this object with another, and returns a numerical result based 75: * on the comparison. If the result is negative, this object sorts less 76: * than the other; if 0, the two are equal, and if positive, this object 77: * sorts greater than the other. To translate this into boolean, simply 78: * perform <code>o1.compareTo(o2) <em><op></em> 0</code>, where op 79: * is one of <, <=, =, !=, >, or >=. 80: * 81: * <p>You must make sure that the comparison is mutual, ie. 82: * <code>sgn(x.compareTo(y)) == -sgn(y.compareTo(x))</code> (where sgn() is 83: * defined as -1, 0, or 1 based on the sign). This includes throwing an 84: * exception in either direction if the two are not comparable; hence, 85: * <code>compareTo(null)</code> should always throw an Exception. 86: * 87: * <p>You should also ensure transitivity, in two forms: 88: * <code>x.compareTo(y) > 0 && y.compareTo(z) > 0</code> implies 89: * <code>x.compareTo(z) > 0</code>; and <code>x.compareTo(y) == 0</code> 90: * implies <code>x.compareTo(z) == y.compareTo(z)</code>. 91: * 92: * @param o the object to be compared 93: * @return an integer describing the comparison 94: * @throws NullPointerException if o is null 95: * @throws ClassCastException if o cannot be compared 96: */ 97: int compareTo(T o); 98: }