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
21 import org.apache.commons.collections4.FunctorException;
22 import org.apache.commons.collections4.Transformer;
23
24 /**
25 * Transformer implementation that always throws an exception.
26 *
27 * @param <T> the type of the input to the function.
28 * @param <R> the type of the result of the function.
29 * @since 3.0
30 */
31 public final class ExceptionTransformer<T, R> implements Transformer<T, R>, Serializable {
32
33 /** Serial version UID */
34 private static final long serialVersionUID = 7179106032121985545L;
35
36 /** Singleton predicate instance */
37 @SuppressWarnings("rawtypes") // the static instance works for all types
38 public static final Transformer INSTANCE = new ExceptionTransformer<>();
39
40 /**
41 * Factory returning the singleton instance.
42 *
43 * @param <I> the input type
44 * @param <O> the output type
45 * @return the singleton instance
46 * @since 3.1
47 */
48 public static <I, O> Transformer<I, O> exceptionTransformer() {
49 return INSTANCE;
50 }
51
52 /**
53 * Restricted constructor.
54 */
55 private ExceptionTransformer() {
56 }
57
58 /**
59 * Returns the singleton instance.
60 *
61 * @return the singleton instance.
62 */
63 private Object readResolve() {
64 return INSTANCE;
65 }
66
67 /**
68 * Transforms the input to result by cloning it.
69 *
70 * @param input the input object to transform
71 * @return never
72 * @throws FunctorException always
73 */
74 @Override
75 public R transform(final T input) {
76 throw new FunctorException("ExceptionTransformer invoked");
77 }
78
79 }