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 030package org.jfree.serializer; 031 032import java.util.Comparator; 033import 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 */ 042public 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}