1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one
3 * or more contributor license agreements. See the NOTICE file
4 * distributed with this work for additional information
5 * regarding copyright ownership. The ASF licenses this file
6 * to you under the Apache License, Version 2.0 (the
7 * "License"); you may not use this file except in compliance
8 * with the License. You may obtain a copy of the License at
9 *
10 * http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing,
13 * software distributed under the License is distributed on an
14 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15 * KIND, either express or implied. See the License for the
16 * specific language governing permissions and limitations
17 * under the License.
18 *
19 */
20 package org.apache.directory.api.ldap.model.filter;
21
22
23 /**
24 * An empty class used for Undefined Nodes.
25 *
26 * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
27 * @version $Rev$, $Date$
28 */
29 public final class UndefinedNode extends AbstractExprNode
30 {
31 /** A static instance of this node */
32 public static final UndefinedNode UNDEFINED_NODE = new UndefinedNode();
33
34
35 /**
36 * Creates a new instance of UndefinedNode.
37 */
38 private UndefinedNode()
39 {
40 super( AssertionType.UNDEFINED );
41 }
42
43
44 /**
45 * {@inheritDoc}
46 *
47 * This implementation always returns false.
48 */
49 public boolean isLeaf()
50 {
51 return false;
52 }
53
54
55 /**
56 * {@inheritDoc}
57 *
58 * This implementation always returns null.
59 */
60 public Object accept( FilterVisitor visitor )
61 {
62 return null;
63 }
64
65
66 /**
67 * {@inheritDoc}
68 */
69 @Override
70 public String toString()
71 {
72 return "Undefined";
73 }
74 }