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)&gt;0) &amp;&amp; (compare(y, z)&gt;0))</tt> implies
071     * <tt>compare(x, z)&gt;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}