001/* 002 * Licensed to the Apache Software Foundation (ASF) under one 003 * or more contributor license agreements. See the NOTICE file 004 * distributed with this work for additional information 005 * regarding copyright ownership. The ASF licenses this file 006 * to you under the Apache License, Version 2.0 (the 007 * "License"); you may not use this file except in compliance 008 * with the License. You may obtain a copy of the License at 009 * 010 * http://www.apache.org/licenses/LICENSE-2.0 011 * 012 * Unless required by applicable law or agreed to in writing, 013 * software distributed under the License is distributed on an 014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY 015 * KIND, either express or implied. See the License for the 016 * specific language governing permissions and limitations 017 * under the License. 018 * 019 */ 020package org.apache.directory.api.ldap.model.filter; 021 022 023/** 024 * An empty class used for Undefined Nodes. 025 * 026 * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a> 027 * @version $Rev$, $Date$ 028 */ 029public final class UndefinedNode extends AbstractExprNode 030{ 031 /** A static instance of this node */ 032 public static final UndefinedNode UNDEFINED_NODE = new UndefinedNode(); 033 034 035 /** 036 * Creates a new instance of UndefinedNode. 037 */ 038 private UndefinedNode() 039 { 040 super( AssertionType.UNDEFINED ); 041 } 042 043 044 /** 045 * {@inheritDoc} 046 * 047 * This implementation always returns false. 048 */ 049 public boolean isLeaf() 050 { 051 return false; 052 } 053 054 055 /** 056 * {@inheritDoc} 057 * 058 * This implementation always returns null. 059 */ 060 public Object accept( FilterVisitor visitor ) 061 { 062 return null; 063 } 064 065 066 /** 067 * {@inheritDoc} 068 */ 069 @Override 070 public String toString() 071 { 072 return "Undefined"; 073 } 074}