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