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.Collections;
25import java.util.List;
26
27/** An ordering that uses the natural order of the values. */
28@GwtCompatible(serializable = true)
29@SuppressWarnings("unchecked") // TODO(kevinb): the right way to explain this??
30final class NaturalOrdering
31    extends Ordering<Comparable> implements Serializable {
32  static final NaturalOrdering INSTANCE = new NaturalOrdering();
33
34  @Override public int compare(Comparable left, Comparable right) {
35    checkNotNull(left); // for GWT
36    checkNotNull(right);
37    if (left == right) {
38      return 0;
39    }
40
41    return left.compareTo(right);
42  }
43
44  @Override public <S extends Comparable> Ordering<S> reverse() {
45    return (Ordering<S>) ReverseNaturalOrdering.INSTANCE;
46  }
47
48  // Override to remove a level of indirection from inner loop
49  @Override public int binarySearch(
50      List<? extends Comparable> sortedList, Comparable key) {
51    return Collections.binarySearch((List) sortedList, key);
52  }
53
54  // Override to remove a level of indirection from inner loop
55  @Override public <E extends Comparable> List<E> sortedCopy(
56      Iterable<E> iterable) {
57    List<E> list = Lists.newArrayList(iterable);
58    Collections.sort(list);
59    return list;
60  }
61
62  // preserving singleton-ness gives equals()/hashCode() for free
63  private Object readResolve() {
64    return INSTANCE;
65  }
66
67  @Override public String toString() {
68    return "Ordering.natural()";
69  }
70
71  private NaturalOrdering() {}
72
73  private static final long serialVersionUID = 0;
74}
75