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.Iterator;
23
24import javax.annotation.Nullable;
25
26/**
27 * An ordering which sorts iterables by comparing corresponding elements
28 * pairwise.
29 */
30@GwtCompatible(serializable = true)
31final class LexicographicalOrdering<T>
32    extends Ordering<Iterable<T>> implements Serializable {
33  final Ordering<? super T> elementOrder;
34
35  LexicographicalOrdering(Ordering<? super T> elementOrder) {
36    this.elementOrder = elementOrder;
37  }
38
39  @Override public int compare(
40      Iterable<T> leftIterable, Iterable<T> rightIterable) {
41    Iterator<T> left = leftIterable.iterator();
42    Iterator<T> right = rightIterable.iterator();
43    while (left.hasNext()) {
44      if (!right.hasNext()) {
45        return LEFT_IS_GREATER; // because it's longer
46      }
47      int result = elementOrder.compare(left.next(), right.next());
48      if (result != 0) {
49        return result;
50      }
51    }
52    if (right.hasNext()) {
53      return RIGHT_IS_GREATER; // because it's longer
54    }
55    return 0;
56  }
57
58  @Override public boolean equals(@Nullable Object object) {
59    if (object == this) {
60      return true;
61    }
62    if (object instanceof LexicographicalOrdering) {
63      LexicographicalOrdering<?> that = (LexicographicalOrdering<?>) object;
64      return this.elementOrder.equals(that.elementOrder);
65    }
66    return false;
67  }
68
69  @Override public int hashCode() {
70    return elementOrder.hashCode() ^ 2075626741; // meaningless
71  }
72
73  @Override public String toString() {
74    return elementOrder + ".lexicographical()";
75  }
76
77  private static final long serialVersionUID = 0;
78}
79