1/*
2 * Copyright (C) 2007 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package com.google.common.collect;
18
19import static com.google.common.base.Preconditions.checkNotNull;
20
21import com.google.common.annotations.GwtCompatible;
22
23import java.io.Serializable;
24import java.util.Iterator;
25
26/** An ordering that uses the reverse of the natural order of the values. */
27@GwtCompatible(serializable = true)
28@SuppressWarnings("unchecked") // TODO(kevinb): the right way to explain this??
29final class ReverseNaturalOrdering
30    extends Ordering<Comparable> implements Serializable {
31  static final ReverseNaturalOrdering INSTANCE = new ReverseNaturalOrdering();
32
33  @Override public int compare(Comparable left, Comparable right) {
34    checkNotNull(left); // right null is caught later
35    if (left == right) {
36      return 0;
37    }
38
39    return right.compareTo(left);
40  }
41
42  @Override public <S extends Comparable> Ordering<S> reverse() {
43    return Ordering.natural();
44  }
45
46  // Override the min/max methods to "hoist" delegation outside loops
47
48  @Override public <E extends Comparable> E min(E a, E b) {
49    return NaturalOrdering.INSTANCE.max(a, b);
50  }
51
52  @Override public <E extends Comparable> E min(E a, E b, E c, E... rest) {
53    return NaturalOrdering.INSTANCE.max(a, b, c, rest);
54  }
55
56  @Override public <E extends Comparable> E min(Iterator<E> iterator) {
57    return NaturalOrdering.INSTANCE.max(iterator);
58  }
59
60  @Override public <E extends Comparable> E min(Iterable<E> iterable) {
61    return NaturalOrdering.INSTANCE.max(iterable);
62  }
63
64  @Override public <E extends Comparable> E max(E a, E b) {
65    return NaturalOrdering.INSTANCE.min(a, b);
66  }
67
68  @Override public <E extends Comparable> E max(E a, E b, E c, E... rest) {
69    return NaturalOrdering.INSTANCE.min(a, b, c, rest);
70  }
71
72  @Override public <E extends Comparable> E max(Iterator<E> iterator) {
73    return NaturalOrdering.INSTANCE.min(iterator);
74  }
75
76  @Override public <E extends Comparable> E max(Iterable<E> iterable) {
77    return NaturalOrdering.INSTANCE.min(iterable);
78  }
79
80  // preserving singleton-ness gives equals()/hashCode() for free
81  private Object readResolve() {
82    return INSTANCE;
83  }
84
85  @Override public String toString() {
86    return "Ordering.natural().reverse()";
87  }
88
89  private ReverseNaturalOrdering() {}
90
91  private static final long serialVersionUID = 0;
92}
93