001 /* ========================================================================
002 * JCommon : a free general purpose class library for the Java(tm) platform
003 * ========================================================================
004 *
005 * (C) Copyright 2000-2005, by Object Refinery Limited and Contributors.
006 *
007 * Project Info: http://www.jfree.org/jcommon/index.html
008 *
009 * This library is free software; you can redistribute it and/or modify it
010 * under the terms of the GNU Lesser General Public License as published by
011 * the Free Software Foundation; either version 2.1 of the License, or
012 * (at your option) any later version.
013 *
014 * This library is distributed in the hope that it will be useful, but
015 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
016 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
017 * License for more details.
018 *
019 * You should have received a copy of the GNU Lesser General Public
020 * License along with this library; if not, write to the Free Software
021 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
022 * USA.
023 *
024 * [Java is a trademark or registered trademark of Sun Microsystems, Inc.
025 * in the United States and other countries.]
026 *
027 * --------------------
028 * ClassComparator.java
029 * --------------------
030 * (C)opyright 2003-2005, by Thomas Morgner and Contributors.
031 *
032 * Original Author: Thomas Morgner (taquera@sherito.org);
033 * Contributor(s): David Gilbert (for Object Refinery Limited);
034 *
035 * $Id: ClassComparator.java,v 1.3 2005/10/18 13:24:19 mungady Exp $
036 *
037 * Changes
038 * -------
039 * 02-May-2003 : Initial version
040 *
041 */
042
043 package org.jfree.util;
044
045 import java.io.Serializable;
046 import java.util.Comparator;
047
048 /**
049 * The class comparator can be used to compare and sort classes and their
050 * superclasses. The comparator is not able to compare classes which have
051 * no relation...
052 *
053 * @author Thomas Morgner
054 */
055 public class ClassComparator implements Comparator, Serializable {
056
057 /** For serialization. */
058 private static final long serialVersionUID = -5225335361837391120L;
059
060 /**
061 * Defaultconstructor.
062 */
063 public ClassComparator() {
064 super();
065 }
066
067 /**
068 * Compares its two arguments for order. Returns a negative integer,
069 * zero, or a positive integer as the first argument is less than, equal
070 * to, or greater than the second.<p>
071 * <P>
072 * Note: throws ClassCastException if the arguments' types prevent them from
073 * being compared by this Comparator.
074 * And IllegalArgumentException if the classes share no relation.
075 *
076 * The implementor must ensure that <tt>sgn(compare(x, y)) ==
077 * -sgn(compare(y, x))</tt> for all <tt>x</tt> and <tt>y</tt>. (This
078 * implies that <tt>compare(x, y)</tt> must throw an exception if and only
079 * if <tt>compare(y, x)</tt> throws an exception.)<p>
080 *
081 * The implementor must also ensure that the relation is transitive:
082 * <tt>((compare(x, y)>0) && (compare(y, z)>0))</tt> implies
083 * <tt>compare(x, z)>0</tt>.<p>
084 *
085 * Finally, the implementer must ensure that <tt>compare(x, y)==0</tt>
086 * implies that <tt>sgn(compare(x, z))==sgn(compare(y, z))</tt> for all
087 * <tt>z</tt>.<p>
088 *
089 * It is generally the case, but <i>not</i> strictly required that
090 * <tt>(compare(x, y)==0) == (x.equals(y))</tt>. Generally speaking,
091 * any comparator that violates this condition should clearly indicate
092 * this fact. The recommended language is "Note: this comparator
093 * imposes orderings that are inconsistent with equals."
094 *
095 * @param o1 the first object to be compared.
096 * @param o2 the second object to be compared.
097 * @return a negative integer, zero, or a positive integer as the
098 * first argument is less than, equal to, or greater than the
099 * second.
100 */
101 public int compare(final Object o1, final Object o2) {
102 final Class c1 = (Class) o1;
103 final Class c2 = (Class) o2;
104 if (c1.equals(o2)) {
105 return 0;
106 }
107 if (c1.isAssignableFrom(c2)) {
108 return -1;
109 }
110 else {
111 if (!c2.isAssignableFrom(c2)) {
112 throw new IllegalArgumentException(
113 "The classes share no relation"
114 );
115 }
116 return 1;
117 }
118 }
119
120 /**
121 * Checks, whether the given classes are comparable. This method will
122 * return true, if one of the classes is assignable from the other class.
123 *
124 * @param c1 the first class to compare
125 * @param c2 the second class to compare
126 * @return true, if the classes share a direct relation, false otherwise.
127 */
128 public boolean isComparable(final Class c1, final Class c2) {
129 return (c1.isAssignableFrom(c2) || c2.isAssignableFrom(c1));
130 }
131 }