Source for org.jfree.util.ClassComparator

   1: /* ========================================================================
   2:  * JCommon : a free general purpose class library for the Java(tm) platform
   3:  * ========================================================================
   4:  *
   5:  * (C) Copyright 2000-2005, by Object Refinery Limited and Contributors.
   6:  * 
   7:  * Project Info:  http://www.jfree.org/jcommon/index.html
   8:  *
   9:  * This library is free software; you can redistribute it and/or modify it 
  10:  * under the terms of the GNU Lesser General Public License as published by 
  11:  * the Free Software Foundation; either version 2.1 of the License, or 
  12:  * (at your option) any later version.
  13:  *
  14:  * This library is distributed in the hope that it will be useful, but 
  15:  * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY 
  16:  * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 
  17:  * License for more details.
  18:  *
  19:  * You should have received a copy of the GNU Lesser General Public
  20:  * License along with this library; if not, write to the Free Software
  21:  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, 
  22:  * USA.  
  23:  *
  24:  * [Java is a trademark or registered trademark of Sun Microsystems, Inc. 
  25:  * in the United States and other countries.]
  26:  *
  27:  * --------------------
  28:  * ClassComparator.java
  29:  * --------------------
  30:  * (C)opyright 2003-2005, by Thomas Morgner and Contributors.
  31:  *
  32:  * Original Author:  Thomas Morgner (taquera@sherito.org);
  33:  * Contributor(s):   David Gilbert (for Object Refinery Limited);
  34:  *
  35:  * $Id: ClassComparator.java,v 1.3 2005/10/18 13:24:19 mungady Exp $
  36:  *
  37:  * Changes
  38:  * -------
  39:  * 02-May-2003 : Initial version
  40:  * 
  41:  */
  42: 
  43: package org.jfree.util;
  44: 
  45: import java.io.Serializable;
  46: import java.util.Comparator;
  47: 
  48: /**
  49:  * The class comparator can be used to compare and sort classes and their
  50:  * superclasses. The comparator is not able to compare classes which have
  51:  * no relation...
  52:  *
  53:  * @author Thomas Morgner
  54:  */
  55: public class ClassComparator implements Comparator, Serializable {
  56: 
  57:     /** For serialization. */
  58:     private static final long serialVersionUID = -5225335361837391120L;
  59:     
  60:     /**
  61:      * Defaultconstructor.
  62:      */
  63:     public ClassComparator() {
  64:         super();
  65:     }
  66: 
  67:     /**
  68:      * Compares its two arguments for order.  Returns a negative integer,
  69:      * zero, or a positive integer as the first argument is less than, equal
  70:      * to, or greater than the second.<p>
  71:      * <P>
  72:      * Note: throws ClassCastException if the arguments' types prevent them from
  73:      * being compared by this Comparator.
  74:      * And IllegalArgumentException if the classes share no relation.
  75:      *
  76:      * The implementor must ensure that <tt>sgn(compare(x, y)) ==
  77:      * -sgn(compare(y, x))</tt> for all <tt>x</tt> and <tt>y</tt>.  (This
  78:      * implies that <tt>compare(x, y)</tt> must throw an exception if and only
  79:      * if <tt>compare(y, x)</tt> throws an exception.)<p>
  80:      *
  81:      * The implementor must also ensure that the relation is transitive:
  82:      * <tt>((compare(x, y)&gt;0) &amp;&amp; (compare(y, z)&gt;0))</tt> implies
  83:      * <tt>compare(x, z)&gt;0</tt>.<p>
  84:      *
  85:      * Finally, the implementer must ensure that <tt>compare(x, y)==0</tt>
  86:      * implies that <tt>sgn(compare(x, z))==sgn(compare(y, z))</tt> for all
  87:      * <tt>z</tt>.<p>
  88:      *
  89:      * It is generally the case, but <i>not</i> strictly required that
  90:      * <tt>(compare(x, y)==0) == (x.equals(y))</tt>.  Generally speaking,
  91:      * any comparator that violates this condition should clearly indicate
  92:      * this fact.  The recommended language is "Note: this comparator
  93:      * imposes orderings that are inconsistent with equals."
  94:      *
  95:      * @param o1 the first object to be compared.
  96:      * @param o2 the second object to be compared.
  97:      * @return a negative integer, zero, or a positive integer as the
  98:      *         first argument is less than, equal to, or greater than the
  99:      *         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: }