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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: DataPage.java,v 1.1 2000/05/06 00:00:31 boisvert Exp $
46   */
47  
48  package jdbm.recman;
49  
50  /**
51   *  Class describing a page that holds data.
52   */
53  final class DataPage extends PageHeader {
54      // offsets
55      private static final short O_FIRST = PageHeader.SIZE; // short firstrowid
56      static final short O_DATA = (short)(O_FIRST + Magic.SZ_SHORT);
57      static final short DATA_PER_PAGE = (short)(RecordFile.BLOCK_SIZE - O_DATA);
58  
59      /**
60       *  Constructs a data page view from the indicated block.
61       */
62      DataPage(BlockIo block) {
63    super(block);
64      }
65  
66      /**
67       *  Factory method to create or return a data page for the
68       *  indicated block.
69       */
70      static DataPage getDataPageView(BlockIo block) {
71    BlockView view = block.getView();
72    if (view != null && view instanceof DataPage)
73        return (DataPage) view;
74    else
75        return new DataPage(block);
76      }
77  
78      /** Returns the first rowid's offset */
79      short getFirst() {
80    return block.readShort(O_FIRST);
81      }
82      
83      /** Sets the first rowid's offset */
84      void setFirst(short value) {
85    paranoiaMagicOk();
86    if (value > 0 && value < O_DATA)
87        throw new Error("DataPage.setFirst: offset " + value 
88            + " too small");
89    block.writeShort(O_FIRST, value);
90      }
91  }