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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    *      https://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  import java.util.function.BiFunction;
21  import java.util.function.Function;
22  
23  /**
24   * Lookups a String key for a String value.
25   * <p>
26   * This class represents the simplest form of a string to string map. It has a benefit over a map in that it can create
27   * the result on demand based on the key.
28   * </p>
29   * <p>
30   * For example, it would be possible to implement a lookup that used the key as a primary key, and looked up the value
31   * on demand from the database.
32   * </p>
33   * <p>
34   * Like {@link BiFunction} is a variant of {@link Function}, this {@code BiStringLookup} is a variant of
35   * {@link StringLookup}.
36   * </p>
37   *
38   * @param <U> The second argument type.
39   * @since 1.9
40   */
41  @FunctionalInterface
42  public interface BiStringLookup<U> extends StringLookup {
43  
44      /**
45       * Looks up a String key to provide a String value.
46       * <p>
47       * The internal implementation may use any mechanism to return the value. The simplest implementation is to use a
48       * Map. However, virtually any implementation is possible.
49       * </p>
50       * <p>
51       * For example, it would be possible to implement a lookup that used the key as a primary key, and looked up the
52       * value on demand from the database Or, a numeric based implementation could be created that treats the key as an
53       * integer, increments the value and return the result as a string - converting 1 to 2, 15 to 16 etc.
54       * </p>
55       * <p>
56       * This method always returns a String, regardless of the underlying data, by converting it as necessary. For
57       * example:
58       * </p>
59       *
60       * <pre>
61       * Map&lt;String, Object&gt; map = new HashMap&lt;String, Object&gt;();
62       * map.put("number", Integer.valueOf(2));
63       * assertEquals("2", StringLookupFactory.biFunctionStringLookup(map).lookup("number", "A context object"));
64       * </pre>
65       *
66       * @param key the key to look up, may be null.
67       * @param object ignored by default.
68       * @return The matching value, null if no match.
69       */
70      default String lookup(final String key, final U object) {
71          return apply(key);
72      }
73  
74  }