- /*
- * 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: 1.20 $ $Date: 2004/05/16 11:49:24 $
- *
- * @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;
- }
- }
-
- }