    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.Closure;
    022import org.apache.commons.collections4.FunctorException;
    023
    024/**
    025 * Closure implementation that always throws an exception.
    026 *
    027 * @param <T> the type of the input to the operation.
    028 * @since 3.0
    029 */
    030public final class ExceptionClosure<T> implements Closure<T>, Serializable {
    031
    032    /** Serial version UID */
    033    private static final long serialVersionUID = 7179106032121985545L;
    034
    035    /** Singleton predicate instance */
    036    @SuppressWarnings("rawtypes") // the static instance works for all types
    037    public static final Closure INSTANCE = new ExceptionClosure<>();
    038
    039    /**
    040     * Factory returning the singleton instance.
    041     *
    042     * @param <T> the type of the input to the operation.
    043     * @return the singleton instance
    044     * @since 3.1
    045     */
    046    public static <T> Closure<T> exceptionClosure() {
    047        return INSTANCE;
    048    }
    049
    050    /**
    051     * Restricted constructor.
    052     */
    053    private ExceptionClosure() {
    054    }
    055
    056    /**
    057     * Always throw an exception.
    058     *
    059     * @param input  the input object
    060     * @throws FunctorException always
    061     */
    062    @Override
    063    public void execute(final T input) {
    064        throw new FunctorException("ExceptionClosure invoked");
    065    }
    066
    067    /**
    068     * Returns the singleton instance.
    069     *
    070     * @return the singleton instance.
    071     */
    072    private Object readResolve() {
    073        return INSTANCE;
    074    }
    075
    076}