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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* 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
* limitations under the License.
*/
package org.apache.commons.collections4.comparators;
import java.io.Serializable;
import java.util.Comparator;
import org.apache.commons.collections4.ComparatorUtils;
/**
* Reverses the order of another comparator by reversing the arguments
* to its {@link #compare(Object, Object) compare} method.
*
* @param the type of objects compared by this comparator
*
* @since 2.0
* @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 final 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 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 {@link java.util.Collections#reverseOrder()}.
*
* @param comparator Comparator to reverse
*/
@SuppressWarnings("unchecked")
public ReverseComparator(final Comparator comparator) {
this.comparator = comparator == null ? ComparatorUtils.NATURAL_COMPARATOR : comparator;
}
//-----------------------------------------------------------------------
/**
* 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
*/
@Override
public int compare(final E obj1, final E 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 3.0
*/
@Override
public int hashCode() {
return "ReverseComparator".hashCode() ^ comparator.hashCode();
}
/**
* Returns true iff that Object is
* is a {@link Comparator} whose ordering is known to be
* equivalent to mine.
*
* This implementation returns true
* iff object.{@link Object#getClass() getClass()}
* equals this.getClass(), 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 3.0
*/
@Override
public boolean equals(final Object object) {
if (this == object) {
return true;
}
if (null == object) {
return false;
}
if (object.getClass().equals(this.getClass())) {
final ReverseComparator thatrc = (ReverseComparator) object;
return comparator.equals(thatrc.comparator);
}
return false;
}
}