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 * https://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.LinkedHashMap;
21 import java.util.Map;
22 import java.util.Objects;
23
24 import org.apache.commons.collections4.Predicate;
25 import org.apache.commons.collections4.Transformer;
26
27 /**
28 * Transformer implementation calls the transformer whose predicate returns true,
29 * like a switch statement.
30 *
31 * @param <T> The type of the input to the function.
32 * @param <R> The type of the result of the function.
33 * @since 3.0
34 */
35 public class SwitchTransformer<T, R> implements Transformer<T, R>, Serializable {
36
37 /** Serial version UID */
38 private static final long serialVersionUID = -6404460890903469332L;
39
40 /**
41 * Create a new Transformer that calls one of the transformers depending
42 * on the predicates.
43 * <p>
44 * The Map consists of Predicate keys and Transformer values. A transformer
45 * is called if its matching predicate returns true. Each predicate is evaluated
46 * until one returns true. If no predicates evaluate to true, the default
47 * transformer is called. The default transformer is set in the map with a
48 * null key. The ordering is that of the iterator() method on the entryset
49 * collection of the map.
50 * </p>
51 *
52 * @param <I> the input type
53 * @param <O> the output type
54 * @param map A map of predicates to transformers
55 * @return The {@code switch} transformer
56 * @throws NullPointerException if the map is null
57 * @throws NullPointerException if any transformer in the map is null
58 * @throws ClassCastException if the map elements are of the wrong type
59 */
60 @SuppressWarnings("unchecked")
61 public static <I, O> Transformer<I, O> switchTransformer(
62 final Map<? extends Predicate<? super I>, ? extends Transformer<? super I, ? extends O>> map) {
63
64 Objects.requireNonNull(map, "map");
65 if (map.isEmpty()) {
66 return ConstantTransformer.<I, O>nullTransformer();
67 }
68 // copy so the caller's map is not mutated; LinkedHashMap preserves iterator() ordering
69 final Map<Predicate<? super I>, Transformer<? super I, ? extends O>> entries = new LinkedHashMap<>(map);
70 final Transformer<? super I, ? extends O> defaultTransformer = entries.remove(null);
71 final int size = entries.size();
72 if (size == 0) {
73 return (Transformer<I, O>) (defaultTransformer == null ? ConstantTransformer.<I, O>nullTransformer() :
74 defaultTransformer);
75 }
76 final Transformer<? super I, ? extends O>[] transformers = new Transformer[size];
77 final Predicate<? super I>[] preds = new Predicate[size];
78 int i = 0;
79 for (final Map.Entry<Predicate<? super I>,
80 Transformer<? super I, ? extends O>> entry : entries.entrySet()) {
81 preds[i] = entry.getKey();
82 transformers[i] = entry.getValue();
83 i++;
84 }
85 return new SwitchTransformer<>(false, preds, transformers, defaultTransformer);
86 }
87
88 /**
89 * Factory method that performs validation and copies the parameter arrays.
90 *
91 * @param <I> the input type
92 * @param <O> the output type
93 * @param predicates array of predicates, cloned, no nulls
94 * @param transformers matching array of transformers, cloned, no nulls
95 * @param defaultTransformer The transformer to use if no match, null means return null
96 * @return The {@code chained} transformer
97 * @throws NullPointerException if either array is null
98 * @throws NullPointerException if any element in the arrays is null
99 * @throws IllegalArgumentException if the arrays have different sizes
100 */
101 @SuppressWarnings("unchecked")
102 public static <I, O> Transformer<I, O> switchTransformer(final Predicate<? super I>[] predicates,
103 final Transformer<? super I, ? extends O>[] transformers,
104 final Transformer<? super I, ? extends O> defaultTransformer) {
105 FunctorUtils.validate(predicates);
106 FunctorUtils.validate(transformers);
107 if (predicates.length != transformers.length) {
108 throw new IllegalArgumentException("The predicate and transformer arrays must be the same size");
109 }
110 if (predicates.length == 0) {
111 return (Transformer<I, O>) (defaultTransformer == null ? ConstantTransformer.<I, O>nullTransformer() :
112 defaultTransformer);
113 }
114 return new SwitchTransformer<>(predicates, transformers, defaultTransformer);
115 }
116
117 /** The tests to consider */
118 private final Predicate<? super T>[] iPredicates;
119
120 /** The matching transformers to call */
121 private final Transformer<? super T, ? extends R>[] iTransformers;
122
123 /** The default transformer to call if no tests match */
124 private final Transformer<? super T, ? extends R> iDefault;
125
126 /**
127 * Hidden constructor for the use by the static factory methods.
128 *
129 * @param clone if {@code true} the input arguments will be cloned
130 * @param predicates array of predicates, no nulls
131 * @param transformers matching array of transformers, no nulls
132 * @param defaultTransformer The transformer to use if no match, null means return null
133 */
134 private SwitchTransformer(final boolean clone, final Predicate<? super T>[] predicates,
135 final Transformer<? super T, ? extends R>[] transformers,
136 final Transformer<? super T, ? extends R> defaultTransformer) {
137 iPredicates = clone ? FunctorUtils.copy(predicates) : predicates;
138 iTransformers = clone ? FunctorUtils.copy(transformers) : transformers;
139 iDefault = defaultTransformer == null ?
140 ConstantTransformer.<T, R>nullTransformer() : defaultTransformer;
141 }
142
143 /**
144 * Constructor that performs no validation.
145 * Use {@code switchTransformer} if you want that.
146 *
147 * @param predicates array of predicates, cloned, no nulls
148 * @param transformers matching array of transformers, cloned, no nulls
149 * @param defaultTransformer The transformer to use if no match, null means return null
150 */
151 public SwitchTransformer(final Predicate<? super T>[] predicates,
152 final Transformer<? super T, ? extends R>[] transformers,
153 final Transformer<? super T, ? extends R> defaultTransformer) {
154 this(true, predicates, transformers, defaultTransformer);
155 }
156
157 /**
158 * Gets the default transformer.
159 *
160 * @return The default transformer
161 * @since 3.1
162 */
163 public Transformer<? super T, ? extends R> getDefaultTransformer() {
164 return iDefault;
165 }
166
167 /**
168 * Gets the predicates.
169 *
170 * @return A copy of the predicates
171 * @since 3.1
172 */
173 public Predicate<? super T>[] getPredicates() {
174 return FunctorUtils.copy(iPredicates);
175 }
176
177 /**
178 * Gets the transformers.
179 *
180 * @return A copy of the transformers
181 * @since 3.1
182 */
183 public Transformer<? super T, ? extends R>[] getTransformers() {
184 return FunctorUtils.copy(iTransformers);
185 }
186
187 /**
188 * Transforms the input to result by calling the transformer whose matching
189 * predicate returns true.
190 *
191 * @param input The input object to transform
192 * @return The transformed result
193 */
194 @Override
195 public R transform(final T input) {
196 for (int i = 0; i < iPredicates.length; i++) {
197 if (iPredicates[i].test(input)) {
198 return iTransformers[i].apply(input);
199 }
200 }
201 return iDefault.apply(input);
202 }
203
204 }