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 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You 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
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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 compare method. 
Author:
Henri Yandell, Michael A. Smith
See Also:
Collections.reverseOrder()
Since:
Commons Collections 2.0
Version:
$Revision: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $/**
 * 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: 646777 $ $Date: 2008-04-10 14:33:15 +0200 (Thu, 10 Apr 2008) $
 *
 * @author Henri Yandell
 * @author Michael A. Smith
 * 
 * @see java.util.Collections#reverseOrder()
 */
public class ReverseComparator implements Comparator, Serializable {

    
Serialization version from Collections 2.0. /** Serialization version from Collections 2.0. */
    private static final long serialVersionUID = 2858887242028539265L;

    
The comparator being decorated. /** 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.reverseOrder().
See Also:
reverseOrder.reverseOrder()/**
     * 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 null, the ReverseComparator defaults to reversing the natural order, as per Collections.reverseOrder().
Params:
comparator – Comparator to reverse/**
     * 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.
Params:
obj1 –  the first object to compare
obj2 –  the second object to compare
Returns:
negative if obj1 is less, positive if greater, zero if equal/**
     * 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 equals. 
Returns:
a suitable hash code
Since:
Commons Collections 3.0/**
     * 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 true iff that Object is is a Comparator whose ordering is known to be equivalent to mine. 

This implementation returns true
iff object.getClass()
equals this.getClass(), and the underlying comparators are equal. Subclasses may want to override this behavior to remain consistent with the equals contract. 
Params:
object –  the object to compare to
Returns:
true if equal
Since:
Commons Collections 3.0/**
     * 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;
        }
    }

}