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}