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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.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      static final int BEFORE_FIRST = -1; 
42      static final int AFTER_LAST = -2; 
43  
44      /**
45       * Tells if the cursor can return a next element
46       * @return true if there are some more elements
47       * @throws IOException 
48       * @throws EndOfFileExceededException 
49       */
50      boolean hasNext() throws EndOfFileExceededException, IOException;
51  
52  
53      /**
54       * Tells if the cursor can return a previous element
55       * @return true if there are some more elements
56       * @throws IOException 
57       * @throws EndOfFileExceededException 
58       */
59      boolean hasPrev() throws EndOfFileExceededException, IOException;
60  
61  
62      /**
63       * Closes the cursor, thus releases the associated transaction
64       */
65      void close();
66  
67  
68      /**
69       * moves the cursor to the same position that was given at the time of instantiating the cursor.
70       * 
71       *  For example, if the cursor was created using browse() method, then beforeFirst() will
72       *  place the cursor before the 0th position.
73       *  
74       *  If the cursor was created using browseFrom(K), then calling beforeFirst() will reset the position
75       *  to the just before the position where K is present.
76       */
77      void beforeFirst() throws IOException;
78  
79  
80      /**
81       * Places the cursor at the end of the last position
82       * 
83       * @throws IOException
84       */
85      public void afterLast() throws IOException;
86  }