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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  }