Mega Code Archive
Class comparator
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/*
* 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
*
*/
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 <tt>sgn(compare(x, y)) ==
* -sgn(compare(y, x))</tt>
* for all <tt>x</tt> and <tt>y</tt>. (This implies that
* <tt>compare(x, y)</tt> must throw an exception if and only if
* <tt>compare(y, x)</tt> throws an exception.)
*
* The implementor must also ensure that the relation is transitive:
* <tt>((compare(x, y)>0) && (compare(y, z)>0))</tt> implies
* <tt>compare(x, z)>0</tt>.
*
* Finally, the implementer must ensure that <tt>compare(x, y)==0</tt>
* implies that <tt>sgn(compare(x, z))==sgn(compare(y, z))</tt> for all
* <tt>z</tt>.
*
* It is generally the case, but <i>not</i> strictly required that
* <tt>(compare(x, y)==0) == (x.equals(y))</tt>. 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));
}
}
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