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 */
017package org.apache.commons.collections4.functors;
018
019import java.io.Serializable;
020
021import org.apache.commons.collections4.FunctorException;
022import org.apache.commons.collections4.Transformer;
023
024/**
025 * Transformer implementation that always throws an exception.
026 *
027 * @since 3.0
028 * @version $Id: ExceptionTransformer.html 887892 2013-11-24 13:43:45Z tn $
029 */
030public final class ExceptionTransformer<I, O> implements Transformer<I, O>, Serializable {
031
032    /** Serial version UID */
033    private static final long serialVersionUID = 7179106032121985545L;
034
035    /** Singleton predicate instance */
036    @SuppressWarnings("rawtypes") // the static instance works for all types
037    public static final Transformer INSTANCE = new ExceptionTransformer<Object, Object>();
038
039    /**
040     * Factory returning the singleton instance.
041     *
042     * @param <I>  the input type
043     * @param <O>  the output type
044     * @return the singleton instance
045     * @since 3.1
046     */
047    @SuppressWarnings("unchecked") // the static instance works for all types
048    public static <I, O> Transformer<I, O> exceptionTransformer() {
049        return (Transformer<I, O>) INSTANCE;
050    }
051
052    /**
053     * Restricted constructor.
054     */
055    private ExceptionTransformer() {
056        super();
057    }
058
059    /**
060     * Transforms the input to result by cloning it.
061     *
062     * @param input  the input object to transform
063     * @return never
064     * @throws FunctorException always
065     */
066    public O transform(final I input) {
067        throw new FunctorException("ExceptionTransformer invoked");
068    }
069
070    private Object readResolve() {
071        return INSTANCE;
072    }
073
074}