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 com.google.common.annotations.GwtCompatible;
20
21import java.io.Serializable;
22
23import javax.annotation.Nullable;
24
25/** An ordering that treats {@code null} as greater than all other values. */
26@GwtCompatible(serializable = true)
27final class NullsLastOrdering<T> extends Ordering<T> implements Serializable {
28  final Ordering<? super T> ordering;
29
30  NullsLastOrdering(Ordering<? super T> ordering) {
31    this.ordering = ordering;
32  }
33
34  @Override public int compare(@Nullable T left, @Nullable T right) {
35    if (left == right) {
36      return 0;
37    }
38    if (left == null) {
39      return LEFT_IS_GREATER;
40    }
41    if (right == null) {
42      return RIGHT_IS_GREATER;
43    }
44    return ordering.compare(left, right);
45  }
46
47  @Override public <S extends T> Ordering<S> reverse() {
48    // ordering.reverse() might be optimized, so let it do its thing
49    return ordering.reverse().nullsFirst();
50  }
51
52  @Override public <S extends T> Ordering<S> nullsFirst() {
53    return ordering.nullsFirst();
54  }
55
56  @SuppressWarnings("unchecked") // still need the right way to explain this
57  @Override public <S extends T> Ordering<S> nullsLast() {
58    return (Ordering<S>) this;
59  }
60
61  @Override public boolean equals(@Nullable Object object) {
62    if (object == this) {
63      return true;
64    }
65    if (object instanceof NullsLastOrdering) {
66      NullsLastOrdering<?> that = (NullsLastOrdering<?>) object;
67      return this.ordering.equals(that.ordering);
68    }
69    return false;
70  }
71
72  @Override public int hashCode() {
73    return ordering.hashCode() ^ -921210296; // meaningless
74  }
75
76  @Override public String toString() {
77    return ordering + ".nullsLast()";
78  }
79
80  private static final long serialVersionUID = 0;
81}
82