    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    /** The map of data to lookup in */
    036    private final Map<? super I, ? extends O> iMap;
    037
    038    /**
    039     * Factory to create the transformer.
    040     * <p>
    041     * If the map is null, a transformer that always returns null is returned.
    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    /**
    056     * Constructor that performs no validation.
    057     * Use <code>mapTransformer</code> 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        super();
    063        iMap = map;
    064    }
    065
    066    /**
    067     * Transforms the input to result by looking it up in a <code>Map</code>.
    068     *
    069     * @param input  the input object to transform
    070     * @return the transformed result
    071     */
    072    @Override
    073    public O transform(final I input) {
    074        return iMap.get(input);
    075    }
    076
    077    /**
    078     * Gets the map to lookup in.
    079     *
    080     * @return the map
    081     * @since 3.1
    082     */
    083    public Map<? super I, ? extends O> getMap() {
    084        return iMap;
    085    }
    086
    087}