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 * @param <T> the type of the input to the function.
028 * @param <R> the type of the result of the function.
029 * @since 3.0
030 */
031public final class ExceptionTransformer<T, R> implements Transformer<T, R>, Serializable {
032
033    /** Serial version UID */
034    private static final long serialVersionUID = 7179106032121985545L;
035
036    /** Singleton predicate instance */
037    @SuppressWarnings("rawtypes") // the static instance works for all types
038    public static final Transformer INSTANCE = new ExceptionTransformer<>();
039
040    /**
041     * Factory returning the singleton instance.
042     *
043     * @param <I>  the input type
044     * @param <O>  the output type
045     * @return the singleton instance
046     * @since 3.1
047     */
048    public static <I, O> Transformer<I, O> exceptionTransformer() {
049        return INSTANCE;
050    }
051
052    /**
053     * Restricted constructor.
054     */
055    private ExceptionTransformer() {
056    }
057
058    /**
059     * Returns the singleton instance.
060     *
061     * @return the singleton instance.
062     */
063    private Object readResolve() {
064        return INSTANCE;
065    }
066
067    /**
068     * Transforms the input to result by cloning it.
069     *
070     * @param input  the input object to transform
071     * @return never
072     * @throws FunctorException always
073     */
074    @Override
075    public R transform(final T input) {
076        throw new FunctorException("ExceptionTransformer invoked");
077    }
078
079}