    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 returns the result of calling
    025 * {@code String.valueOf} on the input object.
    026 *
    027 * @param <T> The type of the input and result to the function.
    028 * @since 3.0
    029 */
    030public final class StringValueTransformer<T> implements Transformer<T, String>, Serializable {
    031
    032    /** Serial version UID */
    033    private static final long serialVersionUID = 7511110693171758606L;
    034
    035    /** Singleton predicate instance */
    036    private static final Transformer<Object, String> INSTANCE = new StringValueTransformer<>();
    037
    038    /**
    039     * Factory returning the singleton instance.
    040     *
    041     * @param <T>  the input type
    042     * @return The singleton instance
    043     * @since 3.1
    044     */
    045    @SuppressWarnings("unchecked")
    046    public static <T> Transformer<T, String> stringValueTransformer() {
    047        return (Transformer<T, String>) INSTANCE;
    048    }
    049
    050    /**
    051     * Restricted constructor.
    052     */
    053    private StringValueTransformer() {
    054    }
    055
    056    /**
    057     * Returns the singleton instance.
    058     *
    059     * @return The singleton instance.
    060     */
    061    private Object readResolve() {
    062        return INSTANCE;
    063    }
    064
    065    /**
    066     * Transforms the input to result by calling {@code String.valueOf}.
    067     *
    068     * @param input  The input object to transform
    069     * @return The transformed result
    070     */
    071    @Override
    072    public String transform(final T input) {
    073        return String.valueOf(input);
    074    }
    075
    076}