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