ReverseOrdering.java revision 1d580d0f6ee4f21eb309ba7b509d2c6d671c4044 
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
26import javax.annotation.Nullable;
27
28/** An ordering that uses the reverse of a given order. */
29@GwtCompatible(serializable = true)
30final class ReverseOrdering<T> extends Ordering<T> implements Serializable {
31  final Ordering<? super T> forwardOrder;
32
33  ReverseOrdering(Ordering<? super T> forwardOrder) {
34    this.forwardOrder = checkNotNull(forwardOrder);
35  }
36
37  @Override public int compare(T a, T b) {
38    return forwardOrder.compare(b, a);
39  }
40
41  @SuppressWarnings("unchecked") // how to explain?
42  @Override public <S extends T> Ordering<S> reverse() {
43    return (Ordering<S>) forwardOrder;
44  }
45
46  // Override the min/max methods to "hoist" delegation outside loops
47
48  @Override public <E extends T> E min(E a, E b) {
49    return forwardOrder.max(a, b);
50  }
51
52  @Override public <E extends T> E min(E a, E b, E c, E... rest) {
53    return forwardOrder.max(a, b, c, rest);
54  }
55
56  @Override public <E extends T> E min(Iterator<E> iterator) {
57    return forwardOrder.max(iterator);
58  }
59
60  @Override public <E extends T> E min(Iterable<E> iterable) {
61    return forwardOrder.max(iterable);
62  }
63
64  @Override public <E extends T> E max(E a, E b) {
65    return forwardOrder.min(a, b);
66  }
67
68  @Override public <E extends T> E max(E a, E b, E c, E... rest) {
69    return forwardOrder.min(a, b, c, rest);
70  }
71
72  @Override public <E extends T> E max(Iterator<E> iterator) {
73    return forwardOrder.min(iterator);
74  }
75
76  @Override public <E extends T> E max(Iterable<E> iterable) {
77    return forwardOrder.min(iterable);
78  }
79
80  @Override public int hashCode() {
81    return -forwardOrder.hashCode();
82  }
83
84  @Override public boolean equals(@Nullable Object object) {
85    if (object == this) {
86      return true;
87    }
88    if (object instanceof ReverseOrdering) {
89      ReverseOrdering<?> that = (ReverseOrdering<?>) object;
90      return this.forwardOrder.equals(that.forwardOrder);
91    }
92    return false;
93  }
94
95  @Override public String toString() {
96    return forwardOrder + ".reverse()";
97  }
98
99  private static final long serialVersionUID = 0;
100}
101