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 * @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}