/*
* Copyright 2001-2004 The Apache Software Foundation
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.commons.collections.comparators;
import java.io.Serializable;
import java.util.Comparator;
/**
* Reverses the order of another comparator by reversing the arguments
* to its {@link #compare(Object, Object) compare} method.
*
* @since Commons Collections 2.0
* @version $Revision: 155406 $ $Date: 2005-02-26 12:55:26 +0000 (Sat, 26 Feb 2005) $
*
* @author Henri Yandell
* @author Michael A. Smith
*
* @see java.util.Collections#reverseOrder()
*/
public class ReverseComparator implements Comparator, Serializable {
/** Serialization version from Collections 2.0. */
private static final long serialVersionUID = 2858887242028539265L;
/** The comparator being decorated. */
private Comparator comparator;
//-----------------------------------------------------------------------
/**
* Creates a comparator that compares objects based on the inverse of their
* natural ordering. Using this Constructor will create a ReverseComparator
* that is functionally identical to the Comparator returned by
* java.util.Collections.<b>reverseOrder()</b>.
*
* @see java.util.Collections#reverseOrder()
*/
public ReverseComparator() {
this(null);
}
/**
* Creates a comparator that inverts the comparison
* of the given comparator. If you pass in <code>null</code>,
* the ReverseComparator defaults to reversing the
* natural order, as per
* {@link java.util.Collections#reverseOrder()}</b>.
*
* @param comparator Comparator to reverse
*/
public ReverseComparator(Comparator comparator) {
if(comparator != null) {
this.comparator = comparator;
} else {
this.comparator = ComparableComparator.getInstance();
}
}
//-----------------------------------------------------------------------
/**
* Compares two objects in reverse order.
*
* @param obj1 the first object to compare
* @param obj2 the second object to compare
* @return negative if obj1 is less, positive if greater, zero if equal
*/
public int compare(Object obj1, Object obj2) {
return comparator.compare(obj2, obj1);
}
//-----------------------------------------------------------------------
/**
* Implement a hash code for this comparator that is consistent with
* {@link #equals(Object) equals}.
*
* @return a suitable hash code
* @since Commons Collections 3.0
*/
public int hashCode() {
return "ReverseComparator".hashCode() ^ comparator.hashCode();
}
/**
* Returns <code>true</code> iff <i>that</i> Object is
* is a {@link Comparator} whose ordering is known to be
* equivalent to mine.
* <p>
* This implementation returns <code>true</code>
* iff <code><i>object</i>.{@link Object#getClass() getClass()}</code>
* equals <code>this.getClass()</code>, and the underlying
* comparators are equal.
* Subclasses may want to override this behavior to remain consistent
* with the {@link Comparator#equals(Object) equals} contract.
*
* @param object the object to compare to
* @return true if equal
* @since Commons Collections 3.0
*/
public boolean equals(Object object) {
if(this == object) {
return true;
} else if(null == object) {
return false;
} else if(object.getClass().equals(this.getClass())) {
ReverseComparator thatrc = (ReverseComparator)object;
return comparator.equals(thatrc.comparator);
} else {
return false;
}
}
}