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.mavibot.btree;
21
22
23 import java.io.IOException;
24 import java.util.NoSuchElementException;
25
26
27 /**
28 * A Cursor which is used when we have no element to return
29 *
30 * @param <K> The type for the Key
31 * @param <V> The type for the stored value
32 *
33 * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
34 */
35 public class EmptyTupleCursor<K, V> extends TupleCursor<K, V>
36 {
37 /** AN empty cursor does not have a revision */
38 private static final long NO_REVISION = -1L;
39
40 /** The creation date */
41 private long creationDate;
42
43
44 /**
45 * Creates a new instance of EmptyTupleCursor. It will never return any result
46 */
47 public EmptyTupleCursor()
48 {
49 super();
50
51 creationDate = System.currentTimeMillis();
52 }
53
54
55 /**
56 * Change the position in the current cursor to set it after the last key
57 */
58 public void afterLast() throws IOException
59 {
60 }
61
62
63 /**
64 * Change the position in the current cursor before the first key
65 */
66 public void beforeFirst() throws IOException
67 {
68 }
69
70
71 /**
72 * Always return false.
73 *
74 * @return Always false
75 */
76 public boolean hasNext()
77 {
78 return false;
79 }
80
81
82 /**
83 * Always throws a NoSuchElementException.
84 *
85 * @return Nothing
86 * @throws NoSuchElementException There is no element in a EmptyTupleCursor
87 */
88 public Tuple<K, V> next() throws NoSuchElementException
89 {
90 throw new NoSuchElementException( "No tuple present" );
91 }
92
93
94 /**
95 * Always throws a NoSuchElementException.
96 *
97 * @return Nothing
98 * @throws NoSuchElementException There is no element in a EmptyTupleCursor
99 */
100 public Tuple<K, V> nextKey() throws NoSuchElementException
101 {
102 // This is the end : no more value
103 throw new NoSuchElementException( "No more tuples present" );
104 }
105
106
107 /**
108 * Always false
109 *
110 * @return false
111 */
112 public boolean hasNextKey()
113 {
114 return false;
115 }
116
117
118 /**
119 * Always false
120 *
121 * @return false
122 */
123 public boolean hasPrev()
124 {
125 return false;
126 }
127
128
129 /**
130 * Always throws a NoSuchElementException.
131 *
132 * @return Nothing
133 * @throws NoSuchElementException There is no element in a EmptyTupleCursor
134 */
135 public Tuple<K, V> prev() throws NoSuchElementException
136 {
137 throw new NoSuchElementException( "No more tuple present" );
138 }
139
140
141 /**
142 * Always throws a NoSuchElementException.
143 *
144 * @return Nothing
145 * @throws NoSuchElementException There is no element in a EmptyTupleCursor
146 */
147 public Tuple<K, V> prevKey() throws NoSuchElementException
148 {
149 throw new NoSuchElementException( "No more tuples present" );
150 }
151
152
153 /**
154 * Always false
155 *
156 * @return false
157 */
158 public boolean hasPrevKey()
159 {
160 return false;
161 }
162
163
164 /**
165 * {@inheritDoc}
166 */
167 public void close()
168 {
169 }
170
171
172 /**
173 * Get the creation date
174 *
175 * @return The creation date for this cursor
176 */
177 public long getCreationDate()
178 {
179 return creationDate;
180 }
181
182
183 /**
184 * Always -1L for an empty cursor
185 *
186 * @return -1L
187 */
188 public long getRevision()
189 {
190 return NO_REVISION;
191 }
192
193
194 /**
195 * @see Object#toString()
196 */
197 public String toString()
198 {
199 return "EmptyTupleCursor";
200 }
201 }