    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 *      https://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.Transformer;
    022
    023/**
    024 * Transformer implementation that does nothing.
    025 *
    026 * @param <T> The type of the input and result to the function.
    027 * @since 3.0
    028 */
    029public class NOPTransformer<T> implements Transformer<T, T>, Serializable {
    030
    031    /** Serial version UID */
    032    private static final long serialVersionUID = 2133891748318574490L;
    033
    034    /** Singleton predicate instance */
    035    @SuppressWarnings("rawtypes")
    036    public static final Transformer INSTANCE = new NOPTransformer<>();
    037
    038    /**
    039     * Factory returning the singleton instance.
    040     *
    041     * @param <T>  the input/output type
    042     * @return The singleton instance
    043     * @since 3.1
    044     */
    045    public static <T> Transformer<T, T> nopTransformer() {
    046        return INSTANCE;
    047    }
    048
    049    /**
    050     * Constructs a new instance.
    051     */
    052    private NOPTransformer() {
    053    }
    054
    055    /**
    056     * Returns the singleton instance.
    057     *
    058     * @return The singleton instance.
    059     */
    060    private Object readResolve() {
    061        return INSTANCE;
    062    }
    063
    064    /**
    065     * Transforms the input to result by doing nothing.
    066     *
    067     * @param input  The input object to transform
    068     * @return The transformed result which is the input
    069     */
    070    @Override
    071    public T transform(final T input) {
    072        return input;
    073    }
    074
    075}