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: } else {
110: if (!c2.isAssignableFrom(c2)) {
111: throw new IllegalArgumentException(
112: "The classes share no relation");
113: }
114: return 1;
115: }
116: }
117:
118: /**
119: * Checks, whether the given classes are comparable. This method will
120: * return true, if one of the classes is assignable from the other class.
121: *
122: * @param c1 the first class to compare
123: * @param c2 the second class to compare
124: * @return true, if the classes share a direct relation, false otherwise.
125: */
126: public boolean isComparable(final Class c1, final Class c2) {
127: return (c1.isAssignableFrom(c2) || c2.isAssignableFrom(c1));
128: }
129: }
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