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    @SuppressWarnings("unchecked") // the static instance works for all types
047    public static <I, O> Transformer<I, O> exceptionTransformer() {
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    @Override
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}