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 import java.util.Objects;
22
23 import org.apache.commons.collections4.Predicate;
24 import org.apache.commons.collections4.Transformer;
25
26 /**
27 * Transformer implementation calls the transformer whose predicate returns true,
28 * like a switch statement.
29 *
30 * @since 3.0
31 */
32 public class SwitchTransformer<I, O> implements Transformer<I, O>, Serializable {
33
34 /** Serial version UID */
35 private static final long serialVersionUID = -6404460890903469332L;
36
37 /**
38 * Create a new Transformer that calls one of the transformers depending
39 * on the predicates.
40 * <p>
41 * The Map consists of Predicate keys and Transformer values. A transformer
42 * is called if its matching predicate returns true. Each predicate is evaluated
43 * until one returns true. If no predicates evaluate to true, the default
44 * transformer is called. The default transformer is set in the map with a
45 * null key. The ordering is that of the iterator() method on the entryset
46 * collection of the map.
47 *
48 * @param <I> the input type
49 * @param <O> the output type
50 * @param map a map of predicates to transformers
51 * @return the {@code switch} transformer
52 * @throws NullPointerException if the map is null
53 * @throws NullPointerException if any transformer in the map is null
54 * @throws ClassCastException if the map elements are of the wrong type
55 */
56 @SuppressWarnings("unchecked")
57 public static <I, O> Transformer<I, O> switchTransformer(
58 final Map<? extends Predicate<? super I>, ? extends Transformer<? super I, ? extends O>> map) {
59
60 Objects.requireNonNull(map, "map");
61 if (map.isEmpty()) {
62 return ConstantTransformer.<I, O>nullTransformer();
63 }
64 // convert to array like this to guarantee iterator() ordering
65 final Transformer<? super I, ? extends O> defaultTransformer = map.remove(null);
66 final int size = map.size();
67 if (size == 0) {
68 return (Transformer<I, O>) (defaultTransformer == null ? ConstantTransformer.<I, O>nullTransformer() :
69 defaultTransformer);
70 }
71 final Transformer<? super I, ? extends O>[] transformers = new Transformer[size];
72 final Predicate<? super I>[] preds = new Predicate[size];
73 int i = 0;
74 for (final Map.Entry<? extends Predicate<? super I>,
75 ? extends Transformer<? super I, ? extends O>> entry : map.entrySet()) {
76 preds[i] = entry.getKey();
77 transformers[i] = entry.getValue();
78 i++;
79 }
80 return new SwitchTransformer<>(false, preds, transformers, defaultTransformer);
81 }
82 /**
83 * Factory method that performs validation and copies the parameter arrays.
84 *
85 * @param <I> the input type
86 * @param <O> the output type
87 * @param predicates array of predicates, cloned, no nulls
88 * @param transformers matching array of transformers, cloned, no nulls
89 * @param defaultTransformer the transformer to use if no match, null means return null
90 * @return the {@code chained} transformer
91 * @throws NullPointerException if either array is null
92 * @throws NullPointerException if any element in the arrays is null
93 * @throws IllegalArgumentException if the arrays have different sizes
94 */
95 @SuppressWarnings("unchecked")
96 public static <I, O> Transformer<I, O> switchTransformer(final Predicate<? super I>[] predicates,
97 final Transformer<? super I, ? extends O>[] transformers,
98 final Transformer<? super I, ? extends O> defaultTransformer) {
99 FunctorUtils.validate(predicates);
100 FunctorUtils.validate(transformers);
101 if (predicates.length != transformers.length) {
102 throw new IllegalArgumentException("The predicate and transformer arrays must be the same size");
103 }
104 if (predicates.length == 0) {
105 return (Transformer<I, O>) (defaultTransformer == null ? ConstantTransformer.<I, O>nullTransformer() :
106 defaultTransformer);
107 }
108 return new SwitchTransformer<>(predicates, transformers, defaultTransformer);
109 }
110 /** The tests to consider */
111 private final Predicate<? super I>[] iPredicates;
112
113 /** The matching transformers to call */
114 private final Transformer<? super I, ? extends O>[] iTransformers;
115
116 /** The default transformer to call if no tests match */
117 private final Transformer<? super I, ? extends O> iDefault;
118
119 /**
120 * Hidden constructor for the use by the static factory methods.
121 *
122 * @param clone if {@code true} the input arguments will be cloned
123 * @param predicates array of predicates, no nulls
124 * @param transformers matching array of transformers, no nulls
125 * @param defaultTransformer the transformer to use if no match, null means return null
126 */
127 private SwitchTransformer(final boolean clone, final Predicate<? super I>[] predicates,
128 final Transformer<? super I, ? extends O>[] transformers,
129 final Transformer<? super I, ? extends O> defaultTransformer) {
130 iPredicates = clone ? FunctorUtils.copy(predicates) : predicates;
131 iTransformers = clone ? FunctorUtils.copy(transformers) : transformers;
132 iDefault = defaultTransformer == null ?
133 ConstantTransformer.<I, O>nullTransformer() : defaultTransformer;
134 }
135
136 /**
137 * Constructor that performs no validation.
138 * Use {@code switchTransformer} if you want that.
139 *
140 * @param predicates array of predicates, cloned, no nulls
141 * @param transformers matching array of transformers, cloned, no nulls
142 * @param defaultTransformer the transformer to use if no match, null means return null
143 */
144 public SwitchTransformer(final Predicate<? super I>[] predicates,
145 final Transformer<? super I, ? extends O>[] transformers,
146 final Transformer<? super I, ? extends O> defaultTransformer) {
147 this(true, predicates, transformers, defaultTransformer);
148 }
149
150 /**
151 * Gets the default transformer.
152 *
153 * @return the default transformer
154 * @since 3.1
155 */
156 public Transformer<? super I, ? extends O> getDefaultTransformer() {
157 return iDefault;
158 }
159
160 /**
161 * Gets the predicates.
162 *
163 * @return a copy of the predicates
164 * @since 3.1
165 */
166 public Predicate<? super I>[] getPredicates() {
167 return FunctorUtils.<I>copy(iPredicates);
168 }
169
170 /**
171 * Gets the transformers.
172 *
173 * @return a copy of the transformers
174 * @since 3.1
175 */
176 public Transformer<? super I, ? extends O>[] getTransformers() {
177 return FunctorUtils.<I, O>copy(iTransformers);
178 }
179
180 /**
181 * Transforms the input to result by calling the transformer whose matching
182 * predicate returns true.
183 *
184 * @param input the input object to transform
185 * @return the transformed result
186 */
187 @Override
188 public O transform(final I input) {
189 for (int i = 0; i < iPredicates.length; i++) {
190 if (iPredicates[i].evaluate(input)) {
191 return iTransformers[i].transform(input);
192 }
193 }
194 return iDefault.transform(input);
195 }
196
197 }