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}