1/*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements.  See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License.  You may obtain a copy of the License at
8 *
9 *      http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17package org.apache.commons.io.comparator;
18
19import java.io.Serializable;
20import java.util.Comparator;
21
22/**
23 * Reverses the result of comparing two objects using
24 * the delegate {@link Comparator}.
25 *
26 * @version $Revision: 609243 $ $Date: 2008-01-06 00:30:42 +0000 (Sun, 06 Jan 2008) $
27 * @since Commons IO 1.4
28 */
29class ReverseComparator<T> implements Comparator<T>, Serializable {
30
31    private final Comparator<T> delegate;
32
33    /**
34     * Construct an instance with the sepecified delegate {@link Comparator}.
35     *
36     * @param delegate The comparator to delegate to
37     */
38    public ReverseComparator(Comparator<T> delegate) {
39        if (delegate == null) {
40            throw new IllegalArgumentException("Delegate comparator is missing");
41        }
42        this.delegate = delegate;
43    }
44
45    /**
46     * Compare using the delegate Comparator, but reversing the result.
47     *
48     * @param obj1 The first object to compare
49     * @param obj2 The second object to compare
50     * @return the result from the delegate {@link Comparator#compare(Object, Object)}
51     * reversing the value (i.e. positive becomes negative and vice versa)
52     */
53    public int compare(T obj1, T obj2) {
54        return delegate.compare(obj2, obj1); // parameters switched round
55    }
56
57}
58