View Javadoc
1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one or more
3    * contributor license agreements. See the NOTICE file distributed with
4    * this work for additional information regarding copyright ownership.
5    * The ASF licenses this file to You under the Apache license, Version 2.0
6    * (the "License"); you may not use this file except in compliance with
7    * the License. You may obtain a copy of the License at
8    *
9    *      http://www.apache.org/licenses/LICENSE-2.0
10   *
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the license for the specific language governing permissions and
15   * limitations under the license.
16   */
17  
18  package org.apache.commons.text.lookup;
19  
20  /**
21   * Lookups a String key for a String value.
22   * <p>
23   * This class represents the simplest form of a string to string map. It has a benefit over a map in that it can create
24   * the result on demand based on the key.
25   * </p>
26   * <p>
27   * For example, it would be possible to implement a lookup that used the key as a primary key, and looked up the value
28   * on demand from the database.
29   * </p>
30   *
31   * @since 1.3
32   */
33  @FunctionalInterface
34  public interface StringLookup {
35  
36      /**
37       * Looks up a String key to provide a String value.
38       * <p>
39       * The internal implementation may use any mechanism to return the value. The simplest implementation is to use a
40       * Map. However, virtually any implementation is possible.
41       * </p>
42       * <p>
43       * For example, it would be possible to implement a lookup that used the key as a primary key, and looked up the
44       * value on demand from the database Or, a numeric based implementation could be created that treats the key as an
45       * integer, increments the value and return the result as a string - converting 1 to 2, 15 to 16 etc.
46       * </p>
47       * <p>
48       * This method always returns a String, regardless of the underlying data, by converting it as necessary. For
49       * example:
50       * </p>
51       *
52       * <pre>
53       * Map&lt;String, Object&gt; map = new HashMap&lt;String, Object&gt;();
54       * map.put("number", new Integer(2));
55       * assertEquals("2", StringLookupFactory.mapStringLookup(map).lookup("number"));
56       * </pre>
57       *
58       * @param key the key to look up, may be null.
59       * @return The matching value, null if no match.
60       */
61      String lookup(String key);
62  }