001    /*
002     *  Licensed to the Apache Software Foundation (ASF) under one or more
003     *  contributor license agreements.  See the NOTICE file distributed with
004     *  this work for additional information regarding copyright ownership.
005     *  The ASF licenses this file to You under the Apache License, Version 2.0
006     *  (the "License"); you may not use this file except in compliance with
007     *  the License.  You may obtain a copy of the License at
008     *
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     *
011     *  Unless required by applicable law or agreed to in writing, software
012     *  distributed under the License is distributed on an "AS IS" BASIS,
013     *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     *  See the License for the specific language governing permissions and
015     *  limitations under the License.
016     */
017    package org.apache.commons.collections.functors;
018    
019    import java.io.Serializable;
020    
021    import org.apache.commons.collections.FunctorException;
022    import org.apache.commons.collections.Transformer;
023    
024    /**
025     * Transformer implementation that always throws an exception.
026     * 
027     * @since Commons Collections 3.0
028     * @version $Revision: 646777 $ $Date: 2008-04-10 13:33:15 +0100 (Thu, 10 Apr 2008) $
029     *
030     * @author Stephen Colebourne
031     */
032    public final class ExceptionTransformer implements Transformer, Serializable {
033    
034        /** Serial version UID */
035        private static final long serialVersionUID = 7179106032121985545L;
036        
037    
038        /** Singleton predicate instance */
039        public static final Transformer INSTANCE = new ExceptionTransformer();
040    
041        /**
042         * Factory returning the singleton instance.
043         * 
044         * @return the singleton instance
045         * @since Commons Collections 3.1
046         */
047        public static Transformer getInstance() {
048            return INSTANCE;
049        }
050    
051        /**
052         * Restricted constructor.
053         */
054        private ExceptionTransformer() {
055            super();
056        }
057    
058        /**
059         * Transforms the input to result by cloning it.
060         * 
061         * @param input  the input object to transform
062         * @return never
063         * @throws FunctorException always
064         */
065        public Object transform(Object input) {
066            throw new FunctorException("ExceptionTransformer invoked");
067        }
068    
069    }