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
21 import org.apache.commons.collections.FunctorException;
22 import org.apache.commons.collections.Transformer;
23
24 /**
25 * Transformer implementation that always throws an exception.
26 *
27 * @since 3.0
28 * @version $Id: ExceptionTransformer.java 1435965 2013-01-20 21:13:18Z tn $
29 */
30 public final class ExceptionTransformer<I, O> implements Transformer<I, O>, Serializable {
31
32 /** Serial version UID */
33 private static final long serialVersionUID = 7179106032121985545L;
34
35 /** Singleton predicate instance */
36 public static final Transformer<Object, Object> INSTANCE = new ExceptionTransformer<Object, Object>();
37
38 /**
39 * Factory returning the singleton instance.
40 *
41 * @param <I> the input type
42 * @param <O> the output type
43 * @return the singleton instance
44 * @since 3.1
45 */
46 @SuppressWarnings("unchecked")
47 public static <I, O> Transformer<I, O> exceptionTransformer() {
48 return (Transformer<I, O>) INSTANCE;
49 }
50
51 /**
52 * Restricted constructor.
53 */
54 private ExceptionTransformer() {
55 super();
56 }
57
58 /**
59 * Transforms the input to result by cloning it.
60 *
61 * @param input the input object to transform
62 * @return never
63 * @throws FunctorException always
64 */
65 public O transform(final I input) {
66 throw new FunctorException("ExceptionTransformer invoked");
67 }
68
69 private Object readResolve() {
70 return INSTANCE;
71 }
72
73 }