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 package org.apache.commons.configuration2.interpol;
18
19 /**
20 * <p>
21 * A simple dummy {@code Lookup} implementation.
22 * </p>
23 * <p>
24 * This implementation always returns <b>null</b> for a passed in variable indicating that it cannot resolve that
25 * variable. This is useful for instance as an application of the <em>null object</em> pattern.
26 * </p>
27 * <p>
28 * This class does not define any state, therefore a single instance can be shared. To enforce usage of only a single
29 * instance this class is actually an enumeration.
30 * </p>
31 *
32 * @since 2.0
33 */
34 public enum DummyLookup implements Lookup {
35 /** The single instance of this class. */
36 INSTANCE;
37
38 /**
39 * {@inheritDoc} This implementation always returns <b>null</b>.
40 */
41 @Override
42 public Object lookup(final String variable) {
43 return null;
44 }
45 }