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.collections.functors;
18
19 import java.io.Serializable;
20 import java.util.Map;
21
22 import org.apache.commons.collections.Predicate;
23 import org.apache.commons.collections.Transformer;
24
25 /**
26 * Transformer implementation calls the transformer whose predicate returns true,
27 * like a switch statement.
28 *
29 * @since 3.0
30 * @version $Id: SwitchTransformer.java 1437000 2013-01-22 15:39:58Z tn $
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 /** The tests to consider */
38 private final Predicate<? super I>[] iPredicates;
39 /** The matching transformers to call */
40 private final Transformer<? super I, ? extends O>[] iTransformers;
41 /** The default transformer to call if no tests match */
42 private final Transformer<? super I, ? extends O> iDefault;
43
44 /**
45 * Factory method that performs validation and copies the parameter arrays.
46 *
47 * @param <I> the input type
48 * @param <O> the output type
49 * @param predicates array of predicates, cloned, no nulls
50 * @param transformers matching array of transformers, cloned, no nulls
51 * @param defaultTransformer the transformer to use if no match, null means return null
52 * @return the <code>chained</code> transformer
53 * @throws IllegalArgumentException if array is null
54 * @throws IllegalArgumentException if any element in the array is null
55 */
56 @SuppressWarnings("unchecked")
57 public static <I, O> Transformer<I, O> switchTransformer(final Predicate<? super I>[] predicates,
58 final Transformer<? super I, ? extends O>[] transformers,
59 final Transformer<? super I, ? extends O> defaultTransformer) {
60 FunctorUtils.validate(predicates);
61 FunctorUtils.validate(transformers);
62 if (predicates.length != transformers.length) {
63 throw new IllegalArgumentException("The predicate and transformer arrays must be the same size");
64 }
65 if (predicates.length == 0) {
66 return (Transformer<I, O>) (defaultTransformer == null ? ConstantTransformer.<I, O>nullTransformer() :
67 defaultTransformer);
68 }
69 return new SwitchTransformer<I, O>(FunctorUtils.copy(predicates),
70 FunctorUtils.copy(transformers),
71 defaultTransformer);
72 }
73
74 /**
75 * Create a new Transformer that calls one of the transformers depending
76 * on the predicates.
77 * <p>
78 * The Map consists of Predicate keys and Transformer values. A transformer
79 * is called if its matching predicate returns true. Each predicate is evaluated
80 * until one returns true. If no predicates evaluate to true, the default
81 * transformer is called. The default transformer is set in the map with a
82 * null key. The ordering is that of the iterator() method on the entryset
83 * collection of the map.
84 *
85 * @param <I> the input type
86 * @param <O> the output type
87 * @param map a map of predicates to transformers
88 * @return the <code>switch</code> transformer
89 * @throws IllegalArgumentException if the map is null
90 * @throws IllegalArgumentException if any transformer in the map is null
91 * @throws ClassCastException if the map elements are of the wrong type
92 */
93 @SuppressWarnings("unchecked")
94 public static <I, O> Transformer<I, O> switchTransformer(
95 final Map<? extends Predicate<? super I>, ? extends Transformer<? super I, ? extends O>> map) {
96
97 if (map == null) {
98 throw new IllegalArgumentException("The predicate and transformer map must not be null");
99 }
100 if (map.size() == 0) {
101 return ConstantTransformer.<I, O>nullTransformer();
102 }
103 // convert to array like this to guarantee iterator() ordering
104 final Transformer<? super I, ? extends O> defaultTransformer = map.remove(null);
105 final int size = map.size();
106 if (size == 0) {
107 return (Transformer<I, O>) (defaultTransformer == null ? ConstantTransformer.<I, O>nullTransformer() :
108 defaultTransformer);
109 }
110 final Transformer<? super I, ? extends O>[] transformers = new Transformer[size];
111 final Predicate<? super I>[] preds = new Predicate[size];
112 int i = 0;
113 for (final Map.Entry<? extends Predicate<? super I>,
114 ? extends Transformer<? super I, ? extends O>> entry : map.entrySet()) {
115 preds[i] = entry.getKey();
116 transformers[i] = entry.getValue();
117 i++;
118 }
119 return new SwitchTransformer<I, O>(preds, transformers, defaultTransformer);
120 }
121
122 /**
123 * Constructor that performs no validation.
124 * Use <code>getInstance</code> if you want that.
125 *
126 * @param predicates array of predicates, not cloned, no nulls
127 * @param transformers matching array of transformers, not cloned, no nulls
128 * @param defaultTransformer the transformer to use if no match, null means return null
129 */
130 @SuppressWarnings("unchecked")
131 public SwitchTransformer(final Predicate<? super I>[] predicates,
132 final Transformer<? super I, ? extends O>[] transformers,
133 final Transformer<? super I, ? extends O> defaultTransformer) {
134 super();
135 iPredicates = predicates;
136 iTransformers = transformers;
137 iDefault = (Transformer<? super I, ? extends O>) (defaultTransformer == null ?
138 ConstantTransformer.<I, O>nullTransformer() : defaultTransformer);
139 }
140
141 /**
142 * Transforms the input to result by calling the transformer whose matching
143 * predicate returns true.
144 *
145 * @param input the input object to transform
146 * @return the transformed result
147 */
148 public O transform(final I input) {
149 for (int i = 0; i < iPredicates.length; i++) {
150 if (iPredicates[i].evaluate(input) == true) {
151 return iTransformers[i].transform(input);
152 }
153 }
154 return iDefault.transform(input);
155 }
156
157 /**
158 * Gets the predicates.
159 *
160 * @return a copy of the predicates
161 * @since 3.1
162 */
163 public Predicate<? super I>[] getPredicates() {
164 return FunctorUtils.<I>copy(iPredicates);
165 }
166
167 /**
168 * Gets the transformers.
169 *
170 * @return a copy of the transformers
171 * @since 3.1
172 */
173 public Transformer<? super I, ? extends O>[] getTransformers() {
174 return FunctorUtils.<I, O>copy(iTransformers);
175 }
176
177 /**
178 * Gets the default transformer.
179 *
180 * @return the default transformer
181 * @since 3.1
182 */
183 public Transformer<? super I, ? extends O> getDefaultTransformer() {
184 return iDefault;
185 }
186
187 }