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: TranslationPage.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 translations from physical rowids
52 * to logical rowids. In fact, the page just holds physical rowids - the
53 * page's block is the block for the logical rowid, the offset serve
54 * as offset for the rowids.
55 */
56 final class TranslationPage extends PageHeader {
57 // offsets
58 static final short O_TRANS = PageHeader.SIZE; // short count
59 static final short ELEMS_PER_PAGE =
60 (RecordFile.BLOCK_SIZE - O_TRANS) / PhysicalRowId.SIZE;
61
62 // slots we returned.
63 final PhysicalRowId[] slots = new PhysicalRowId[ELEMS_PER_PAGE];
64
65 /**
66 * Constructs a data page view from the indicated block.
67 */
68 TranslationPage(BlockIo block) {
69 super(block);
70 }
71
72 /**
73 * Factory method to create or return a data page for the
74 * indicated block.
75 */
76 static TranslationPage getTranslationPageView(BlockIo block) {
77 BlockView view = block.getView();
78 if (view != null && view instanceof TranslationPage)
79 return (TranslationPage) view;
80 else
81 return new TranslationPage(block);
82 }
83
84 /** Returns the value of the indicated rowid on the page */
85 PhysicalRowId get(short offset) {
86 int slot = (offset - O_TRANS) / PhysicalRowId.SIZE;
87 if (slots[slot] == null)
88 slots[slot] = new PhysicalRowId(block, offset);
89 return slots[slot];
90 }
91 }