/* ======================================================================== * JCommon : a free general purpose class library for the Java(tm) platform * ======================================================================== * * (C) Copyright 2000-2005, by Object Refinery Limited and Contributors. * * Project Info: http://www.jfree.org/jcommon/index.html * * This library is free software; you can redistribute it and/or modify it * under the terms of the GNU Lesser General Public License as published by * the Free Software Foundation; either version 2.1 of the License, or * (at your option) any later version. * * This library is distributed in the hope that it will be useful, but * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public * License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with this library; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, * USA. * * [Java is a trademark or registered trademark of Sun Microsystems, Inc. * in the United States and other countries.] * * -------------------- * ClassComparator.java * -------------------- * (C)opyright 2003-2005, by Thomas Morgner and Contributors. * * Original Author: Thomas Morgner (taquera@sherito.org); * Contributor(s): David Gilbert (for Object Refinery Limited); * * $Id: ClassComparator.java,v 1.3 2005/10/18 13:24:19 mungady Exp $ * * Changes * ------- * 02-May-2003 : Initial version * */ package org.jfree.util; import java.io.Serializable; import java.util.Comparator; /** * The class comparator can be used to compare and sort classes and their * superclasses. The comparator is not able to compare classes which have * no relation... * * @author Thomas Morgner */ public class ClassComparator implements Comparator, Serializable { /** For serialization. */ private static final long serialVersionUID = -5225335361837391120L; /** * Defaultconstructor. */ public ClassComparator() { super(); } /** * Compares its two arguments for order. Returns a negative integer, * zero, or a positive integer as the first argument is less than, equal * to, or greater than the second.
*
* Note: throws ClassCastException if the arguments' types prevent them from * being compared by this Comparator. * And IllegalArgumentException if the classes share no relation. * * The implementor must ensure that sgn(compare(x, y)) == * -sgn(compare(y, x)) for all x and y. (This * implies that compare(x, y) must throw an exception if and only * if compare(y, x) throws an exception.)
* * The implementor must also ensure that the relation is transitive: * ((compare(x, y)>0) && (compare(y, z)>0)) implies * compare(x, z)>0.
* * Finally, the implementer must ensure that compare(x, y)==0 * implies that sgn(compare(x, z))==sgn(compare(y, z)) for all * z.
* * It is generally the case, but not strictly required that * (compare(x, y)==0) == (x.equals(y)). Generally speaking, * any comparator that violates this condition should clearly indicate * this fact. The recommended language is "Note: this comparator * imposes orderings that are inconsistent with equals." * * @param o1 the first object to be compared. * @param o2 the second object to be compared. * @return a negative integer, zero, or a positive integer as the * first argument is less than, equal to, or greater than the * second. */ public int compare(final Object o1, final Object o2) { final Class c1 = (Class) o1; final Class c2 = (Class) o2; if (c1.equals(o2)) { return 0; } if (c1.isAssignableFrom(c2)) { return -1; } else { if (!c2.isAssignableFrom(c2)) { throw new IllegalArgumentException( "The classes share no relation" ); } return 1; } } /** * Checks, whether the given classes are comparable. This method will * return true, if one of the classes is assignable from the other class. * * @param c1 the first class to compare * @param c2 the second class to compare * @return true, if the classes share a direct relation, false otherwise. */ public boolean isComparable(final Class c1, final Class c2) { return (c1.isAssignableFrom(c2) || c2.isAssignableFrom(c1)); } }