    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}