    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;
    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     *
    042     * @param <I>  the input type
    043     * @param <O>  the output type
    044     * @param map the map, not cloned
    045     * @return the transformer
    046     */
    047    public static <I, O> Transformer<I, O> mapTransformer(final Map<? super I, ? extends O> map) {
    048        if (map == null) {
    049            return ConstantTransformer.<I, O>nullTransformer();
    050        }
    051        return new MapTransformer<>(map);
    052    }
    053
    054    /** The map of data to lookup in */
    055    private final Map<? super T, ? extends R> iMap;
    056
    057    /**
    058     * Constructor that performs no validation.
    059     * Use {@code mapTransformer} if you want that.
    060     *
    061     * @param map  the map to use for lookup, not cloned
    062     */
    063    private MapTransformer(final Map<? super T, ? extends R> map) {
    064        iMap = map;
    065    }
    066
    067    /**
    068     * Gets the map to lookup in.
    069     *
    070     * @return the map
    071     * @since 3.1
    072     */
    073    public Map<? super T, ? extends R> getMap() {
    074        return iMap;
    075    }
    076
    077    /**
    078     * Transforms the input to result by looking it up in a {@code Map}.
    079     *
    080     * @param input  the input object to transform
    081     * @return the transformed result
    082     */
    083    @Override
    084    public R transform(final T input) {
    085        return iMap.get(input);
    086    }
    087
    088}