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;
22import com.google.common.base.Function;
23import com.google.common.base.Objects;
24
25import java.io.Serializable;
26
27import javax.annotation.Nullable;
28
29/**
30 * An ordering that orders elements by applying an order to the result of a
31 * function on those elements.
32 */
33@GwtCompatible(serializable = true)
34final class ByFunctionOrdering<F, T>
35    extends Ordering<F> implements Serializable {
36  final Function<F, ? extends T> function;
37  final Ordering<T> ordering;
38
39  ByFunctionOrdering(
40      Function<F, ? extends T> function, Ordering<T> ordering) {
41    this.function = checkNotNull(function);
42    this.ordering = checkNotNull(ordering);
43  }
44
45  @Override public int compare(F left, F right) {
46    return ordering.compare(function.apply(left), function.apply(right));
47  }
48
49  @Override public boolean equals(@Nullable Object object) {
50    if (object == this) {
51      return true;
52    }
53    if (object instanceof ByFunctionOrdering) {
54      ByFunctionOrdering<?, ?> that = (ByFunctionOrdering<?, ?>) object;
55      return this.function.equals(that.function)
56          && this.ordering.equals(that.ordering);
57    }
58    return false;
59  }
60
61  @Override public int hashCode() {
62    return Objects.hashCode(function, ordering);
63  }
64
65  @Override public String toString() {
66    return ordering + ".onResultOf(" + function + ")";
67  }
68
69  private static final long serialVersionUID = 0;
70}
71