001 /**
002 * ===================================================
003 * JCommon-Serializer : a free serialization framework
004 * ===================================================
005 *
006 * Project Info: http://reporting.pentaho.org/jcommon-serializer/
007 *
008 * (C) Copyright 2006-2008, by Object Refinery Limited, Pentaho Corporation and Contributors.
009 *
010 * This library is free software; you can redistribute it and/or modify it under the terms
011 * of the GNU Lesser General Public License as published by the Free Software Foundation;
012 * either version 2.1 of the License, or (at your option) any later version.
013 *
014 * This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
015 * without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
016 * See the GNU Lesser General Public License for more details.
017 *
018 * You should have received a copy of the GNU Lesser General Public License along with this
019 * library; if not, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330,
020 * Boston, MA 02111-1307, USA.
021 *
022 * [Java is a trademark or registered trademark of Sun Microsystems, Inc.
023 * in the United States and other countries.]
024 *
025 * ------------
026 * ClassComparator
027 * ------------
028 */
029
030 package org.jfree.serializer;
031
032 import java.util.Comparator;
033 import java.io.Serializable;
034
035 /**
036 * The class comparator can be used to compare and sort classes and their
037 * superclasses. The comparator is not able to compare classes which have
038 * no relation...
039 *
040 * @author Thomas Morgner
041 */
042 public class ClassComparator implements Comparator, Serializable
043 {
044
045 /** For serialization. */
046 private static final long serialVersionUID = -5225335361837391120L;
047
048 /**
049 * Defaultconstructor.
050 */
051 public ClassComparator() {
052 super();
053 }
054
055 /**
056 * Compares its two arguments for order. Returns a negative integer,
057 * zero, or a positive integer as the first argument is less than, equal
058 * to, or greater than the second.<p>
059 * <P>
060 * Note: throws ClassCastException if the arguments' types prevent them from
061 * being compared by this Comparator.
062 * And IllegalArgumentException if the classes share no relation.
063 *
064 * The implementor must ensure that <tt>sgn(compare(x, y)) ==
065 * -sgn(compare(y, x))</tt> for all <tt>x</tt> and <tt>y</tt>. (This
066 * implies that <tt>compare(x, y)</tt> must throw an exception if and only
067 * if <tt>compare(y, x)</tt> throws an exception.)<p>
068 *
069 * The implementor must also ensure that the relation is transitive:
070 * <tt>((compare(x, y)>0) && (compare(y, z)>0))</tt> implies
071 * <tt>compare(x, z)>0</tt>.<p>
072 *
073 * Finally, the implementer must ensure that <tt>compare(x, y)==0</tt>
074 * implies that <tt>sgn(compare(x, z))==sgn(compare(y, z))</tt> for all
075 * <tt>z</tt>.<p>
076 *
077 * It is generally the case, but <i>not</i> strictly required that
078 * <tt>(compare(x, y)==0) == (x.equals(y))</tt>. Generally speaking,
079 * any comparator that violates this condition should clearly indicate
080 * this fact. The recommended language is "Note: this comparator
081 * imposes orderings that are inconsistent with equals."
082 *
083 * @param o1 the first object to be compared.
084 * @param o2 the second object to be compared.
085 * @return a negative integer, zero, or a positive integer as the
086 * first argument is less than, equal to, or greater than the
087 * second.
088 */
089 public int compare(final Object o1, final Object o2) {
090 final Class c1 = (Class) o1;
091 final Class c2 = (Class) o2;
092 if (c1.equals(o2)) {
093 return 0;
094 }
095 if (c1.isAssignableFrom(c2)) {
096 return -1;
097 }
098 else {
099 if (!c2.isAssignableFrom(c2)) {
100 throw new IllegalArgumentException(
101 "The classes share no relation"
102 );
103 }
104 return 1;
105 }
106 }
107
108 /**
109 * Checks, whether the given classes are comparable. This method will
110 * return true, if one of the classes is assignable from the other class.
111 *
112 * @param c1 the first class to compare
113 * @param c2 the second class to compare
114 * @return true, if the classes share a direct relation, false otherwise.
115 */
116 public boolean isComparable(final Class c1, final Class c2) {
117 return (c1.isAssignableFrom(c2) || c2.isAssignableFrom(c1));
118 }
119 }