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