    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;
    020import java.util.Map;
    021
    022import org.apache.commons.collections4.Transformer;
    023
    024/**
    025 * Transformer implementation that returns the value held in a specified map
    026 * using the input parameter as a key.
    027 *
    028 * @param <T> The type of the input to the function.
    029 * @param <R> The type of the result of the function.
    030 * @since 3.0
    031 */
    032public final class MapTransformer<T, R> implements Transformer<T, R>, Serializable {
    033
    034    /** Serial version UID */
    035    private static final long serialVersionUID = 862391807045468939L;
    036
    037    /**
    038     * Creates the transformer.
    039     * <p>
    040     * If the map is null, a transformer that always returns null is returned.
    041     * </p>
    042     *
    043     * @param <I>  the input type
    044     * @param <O>  the output type
    045     * @param map The map, not cloned
    046     * @return The transformer
    047     */
    048    public static <I, O> Transformer<I, O> mapTransformer(final Map<? super I, ? extends O> map) {
    049        if (map == null) {
    050            return ConstantTransformer.<I, O>nullTransformer();
    051        }
    052        return new MapTransformer<>(map);
    053    }
    054
    055    /** The map of data to lookup in */
    056    private final Map<? super T, ? extends R> iMap;
    057
    058    /**
    059     * Constructor that performs no validation.
    060     * Use {@code mapTransformer} if you want that.
    061     *
    062     * @param map  The map to use for lookup, not cloned
    063     */
    064    private MapTransformer(final Map<? super T, ? extends R> map) {
    065        iMap = map;
    066    }
    067
    068    /**
    069     * Gets the map to lookup in.
    070     *
    071     * @return The map
    072     * @since 3.1
    073     */
    074    public Map<? super T, ? extends R> getMap() {
    075        return iMap;
    076    }
    077
    078    /**
    079     * Transforms the input to result by looking it up in a {@code Map}.
    080     *
    081     * @param input  The input object to transform
    082     * @return The transformed result
    083     */
    084    @Override
    085    public R transform(final T input) {
    086        return iMap.get(input);
    087    }
    088
    089}