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 */ 017 018package org.apache.commons.text.lookup; 019 020/** 021 * Lookup a String key to a String value. 022 * <p> 023 * This class represents the simplest form of a string to string map. It has a benefit over a map in that it can create 024 * the result on demand based on the key. 025 * </p> 026 * <p> 027 * For example, it would be possible to implement a lookup that used the key as a primary key, and looked up the value 028 * on demand from the database 029 * </p> 030 * 031 * @since 1.3 032 */ 033public interface StringLookup { 034 035 /** 036 * Looks up a String key to a String value. 037 * <p> 038 * The internal implementation may use any mechanism to return the value. The simplest implementation is to use a 039 * Map. However, virtually any implementation is possible. 040 * </p> 041 * <p> 042 * For example, it would be possible to implement a lookup that used the key as a primary key, and looked up the 043 * value on demand from the database Or, a numeric based implementation could be created that treats the key as an 044 * integer, increments the value and return the result as a string - converting 1 to 2, 15 to 16 etc. 045 * </p> 046 * <p> 047 * This method always returns a String, regardless of the underlying data, by converting it as necessary. For 048 * example: 049 * </p> 050 * 051 * <pre> 052 * Map<String, Object> map = new HashMap<String, Object>(); 053 * map.put("number", new Integer(2)); 054 * assertEquals("2", StringLookupFactory.mapStringLookup(map).lookup("number")); 055 * </pre> 056 * 057 * @param key 058 * the key to look up, may be null 059 * @return the matching value, null if no match 060 */ 061 String lookup(String key); 062}