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