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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   * @since 3.0
28   */
29  public final class ExceptionTransformer<I, O> implements Transformer<I, O>, Serializable {
30  
31      /** Serial version UID */
32      private static final long serialVersionUID = 7179106032121985545L;
33  
34      /** Singleton predicate instance */
35      @SuppressWarnings("rawtypes") // the static instance works for all types
36      public static final Transformer INSTANCE = new ExceptionTransformer<>();
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      public static <I, O> Transformer<I, O> exceptionTransformer() {
47          return INSTANCE;
48      }
49  
50      /**
51       * Restricted constructor.
52       */
53      private ExceptionTransformer() {
54          super();
55      }
56  
57      /**
58       * Transforms the input to result by cloning it.
59       *
60       * @param input  the input object to transform
61       * @return never
62       * @throws FunctorException always
63       */
64      @Override
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  }