1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.collections4.functors;
18
19 import java.io.Serializable;
20 import java.util.Map;
21
22 import org.apache.commons.collections4.Transformer;
23
24 /**
25 * Transformer implementation that returns the value held in a specified map
26 * using the input parameter as a key.
27 *
28 * @param <T> the type of the input to the function.
29 * @param <R> the type of the result of the function.
30 * @since 3.0
31 */
32 public final class MapTransformer<T, R> implements Transformer<T, R>, Serializable {
33
34 /** Serial version UID */
35 private static final long serialVersionUID = 862391807045468939L;
36
37 /**
38 * Creates the transformer.
39 * <p>
40 * If the map is null, a transformer that always returns null is returned.
41 *
42 * @param <I> the input type
43 * @param <O> the output type
44 * @param map the map, not cloned
45 * @return the transformer
46 */
47 public static <I, O> Transformer<I, O> mapTransformer(final Map<? super I, ? extends O> map) {
48 if (map == null) {
49 return ConstantTransformer.<I, O>nullTransformer();
50 }
51 return new MapTransformer<>(map);
52 }
53
54 /** The map of data to lookup in */
55 private final Map<? super T, ? extends R> iMap;
56
57 /**
58 * Constructor that performs no validation.
59 * Use {@code mapTransformer} if you want that.
60 *
61 * @param map the map to use for lookup, not cloned
62 */
63 private MapTransformer(final Map<? super T, ? extends R> map) {
64 iMap = map;
65 }
66
67 /**
68 * Gets the map to lookup in.
69 *
70 * @return the map
71 * @since 3.1
72 */
73 public Map<? super T, ? extends R> getMap() {
74 return iMap;
75 }
76
77 /**
78 * Transforms the input to result by looking it up in a {@code Map}.
79 *
80 * @param input the input object to transform
81 * @return the transformed result
82 */
83 @Override
84 public R transform(final T input) {
85 return iMap.get(input);
86 }
87
88 }