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;
22import java.util.List;
23
24import javax.annotation.Nullable;
25
26/** An ordering that compares objects according to a given order. */
27@GwtCompatible(serializable = true)
28final class ExplicitOrdering<T> extends Ordering<T> implements Serializable {
29  final ImmutableMap<T, Integer> rankMap;
30
31  ExplicitOrdering(List<T> valuesInOrder) {
32    this(buildRankMap(valuesInOrder));
33  }
34
35  ExplicitOrdering(ImmutableMap<T, Integer> rankMap) {
36    this.rankMap = rankMap;
37  }
38
39  @Override public int compare(T left, T right) {
40    return rank(left) - rank(right); // safe because both are nonnegative
41  }
42
43  private int rank(T value) {
44    Integer rank = rankMap.get(value);
45    if (rank == null) {
46      throw new IncomparableValueException(value);
47    }
48    return rank;
49  }
50
51  private static <T> ImmutableMap<T, Integer> buildRankMap(
52      List<T> valuesInOrder) {
53    ImmutableMap.Builder<T, Integer> builder = ImmutableMap.builder();
54    int rank = 0;
55    for (T value : valuesInOrder) {
56      builder.put(value, rank++);
57    }
58    return builder.build();
59  }
60
61  @Override public boolean equals(@Nullable Object object) {
62    if (object instanceof ExplicitOrdering) {
63      ExplicitOrdering<?> that = (ExplicitOrdering<?>) object;
64      return this.rankMap.equals(that.rankMap);
65    }
66    return false;
67  }
68
69  @Override public int hashCode() {
70    return rankMap.hashCode();
71  }
72
73  @Override public String toString() {
74    return "Ordering.explicit(" + rankMap.keySet() + ")";
75  }
76
77  private static final long serialVersionUID = 0;
78}
79