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1   /**
2    * JDBM LICENSE v1.00
3    *
4    * Redistribution and use of this software and associated documentation
5    * ("Software"), with or without modification, are permitted provided
6    * that the following conditions are met:
7    *
8    * 1. Redistributions of source code must retain copyright
9    *    statements and notices.  Redistributions must also contain a
10   *    copy of this document.
11   *
12   * 2. Redistributions in binary form must reproduce the
13   *    above copyright notice, this list of conditions and the
14   *    following disclaimer in the documentation and/or other
15   *    materials provided with the distribution.
16   *
17   * 3. The name "JDBM" must not be used to endorse or promote
18   *    products derived from this Software without prior written
19   *    permission of Cees de Groot.  For written permission,
20   *    please contact cg@cdegroot.com.
21   *
22   * 4. Products derived from this Software may not be called "JDBM"
23   *    nor may "JDBM" appear in their names without prior written
24   *    permission of Cees de Groot. 
25   *
26   * 5. Due credit should be given to the JDBM Project
27   *    (http://jdbm.sourceforge.net/).
28   *
29   * THIS SOFTWARE IS PROVIDED BY THE JDBM PROJECT AND CONTRIBUTORS
30   * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
31   * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
32   * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL
33   * CEES DE GROOT OR ANY CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
34   * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
35   * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
36   * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
37   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
38   * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
39   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
40   * OF THE POSSIBILITY OF SUCH DAMAGE.
41   *
42   * Copyright 2000 (C) Cees de Groot. All Rights Reserved.
43   * Contributions are Copyright (C) 2000 by their associated contributors.
44   *
45   * $Id: PageCursor.java,v 1.1 2000/05/06 00:00:31 boisvert Exp $
46   */
47  
48  package jdbm.recman;
49  
50  import java.io.IOException;
51  
52  /**
53   *  This class provides a cursor that can follow lists of pages
54   *  bi-directionally.
55   */
56  final class PageCursor {
57      PageManager pageman;
58      long current;
59      short type;
60      
61      /**
62       *  Constructs a page cursor that starts at the indicated block.
63       */
64      PageCursor(PageManager pageman, long current) {
65          this.pageman = pageman;
66          this.current = current;
67      }
68      
69      /**
70       *  Constructs a page cursor that starts at the first block
71       *  of the indicated list.
72       */
73      PageCursor(PageManager pageman, short type) throws IOException {
74          this.pageman = pageman;
75          this.type = type;
76      }
77      
78      /**
79       *  Returns the current value of the cursor.
80       */
81      long getCurrent() throws IOException {
82          return current;
83      }
84      
85      /**
86       *  Returns the next value of the cursor
87       */
88      long next() throws IOException {
89          if (current == 0)
90              current = pageman.getFirst(type);
91          else
92              current = pageman.getNext(current);
93          return current;
94      } 
95      
96      /**
97       *  Returns the previous value of the cursor
98       */
99      long prev() throws IOException {
100         current = pageman.getPrev(current);
101         return current;
102     }
103 }