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 * @version $Id: MapTransformer.html 972421 2015-11-14 20:00:04Z tn $
030 */
031public final class MapTransformer<I, O> implements Transformer<I, O>, Serializable {
032
033    /** Serial version UID */
034    private static final long serialVersionUID = 862391807045468939L;
035
036    /** The map of data to lookup in */
037    private final Map<? super I, ? extends O> iMap;
038
039    /**
040     * Factory to create the transformer.
041     * <p>
042     * If the map is null, a transformer that always returns null is returned.
043     *
044     * @param <I>  the input type
045     * @param <O>  the output type
046     * @param map the map, not cloned
047     * @return the transformer
048     */
049    public static <I, O> Transformer<I, O> mapTransformer(final Map<? super I, ? extends O> map) {
050        if (map == null) {
051            return ConstantTransformer.<I, O>nullTransformer();
052        }
053        return new MapTransformer<I, O>(map);
054    }
055
056    /**
057     * Constructor that performs no validation.
058     * Use <code>mapTransformer</code> if you want that.
059     *
060     * @param map  the map to use for lookup, not cloned
061     */
062    private MapTransformer(final Map<? super I, ? extends O> map) {
063        super();
064        iMap = map;
065    }
066
067    /**
068     * Transforms the input to result by looking it up in a <code>Map</code>.
069     *
070     * @param input  the input object to transform
071     * @return the transformed result
072     */
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}