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 * Lookups a String key for 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 */
033@FunctionalInterface
034public interface StringLookup {
035
036    /**
037     * Looks up a String key to provide a String value.
038     * <p>
039     * The internal implementation may use any mechanism to return the value. The simplest implementation is to use a
040     * Map. However, virtually any implementation is possible.
041     * </p>
042     * <p>
043     * For example, it would be possible to implement a lookup that used the key as a primary key, and looked up the
044     * value on demand from the database Or, a numeric based implementation could be created that treats the key as an
045     * integer, increments the value and return the result as a string - converting 1 to 2, 15 to 16 etc.
046     * </p>
047     * <p>
048     * This method always returns a String, regardless of the underlying data, by converting it as necessary. For
049     * example:
050     * </p>
051     *
052     * <pre>
053     * Map&lt;String, Object&gt; map = new HashMap&lt;String, Object&gt;();
054     * map.put("number", new Integer(2));
055     * assertEquals("2", StringLookupFactory.mapStringLookup(map).lookup("number"));
056     * </pre>
057     *
058     * @param key the key to look up, may be null.
059     * @return The matching value, null if no match.
060     */
061    String lookup(String key);
062}