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}