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
25 import org.apache.directory.mavibot.btree.exception.EndOfFileExceededException;
26
27
28 /**
29 * A Cursor is used to fetch elements in a BTree and is returned by the
30 * @see BTree#browse method. The cursor <strng>must</strong> be closed
31 * when the user is done with it.
32 * <p>
33 *
34 * @param <K> The type for the Key
35 *
36 * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
37 */
38 public interface Cursor<K>
39 {
40 /** Static value for the beforeFrst and afterLast positions */
41 int BEFORE_FIRST = -1;
42 int AFTER_LAST = -2;
43
44
45 /**
46 * Tells if the cursor can return a next element
47 * @return true if there are some more elements
48 * @throws IOException
49 * @throws EndOfFileExceededException
50 */
51 boolean hasNext() throws EndOfFileExceededException, IOException;
52
53
54 /**
55 * Tells if the cursor can return a previous element
56 * @return true if there are some more elements
57 * @throws IOException
58 * @throws EndOfFileExceededException
59 */
60 boolean hasPrev() throws EndOfFileExceededException, IOException;
61
62
63 /**
64 * Closes the cursor, thus releases the associated transaction
65 */
66 void close();
67
68
69 /**
70 * moves the cursor to the same position that was given at the time of instantiating the cursor.
71 *
72 * For example, if the cursor was created using browse() method, then beforeFirst() will
73 * place the cursor before the 0th position.
74 *
75 * If the cursor was created using browseFrom(K), then calling beforeFirst() will reset the position
76 * to the just before the position where K is present.
77 */
78 void beforeFirst() throws IOException;
79
80
81 /**
82 * Places the cursor at the end of the last position
83 *
84 * @throws IOException
85 */
86 void afterLast() throws IOException;
87 }