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 }