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}