    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}