01: /**
02: * JDBM LICENSE v1.00
03: *
04: * Redistribution and use of this software and associated documentation
05: * ("Software"), with or without modification, are permitted provided
06: * that the following conditions are met:
07: *
08: * 1. Redistributions of source code must retain copyright
09: * 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: */package jdbm.recman;
47:
48: /**
49: * Class describing a page that holds translations from physical rowids
50: * to logical rowids. In fact, the page just holds physical rowids - the
51: * page's block is the block for the logical rowid, the offset serve
52: * as offset for the rowids.
53: */
54: final class TranslationPage extends PageHeader {
55: // offsets
56: static final short O_TRANS = PageHeader.SIZE; // short count
57: static final short ELEMS_PER_PAGE = (RecordFile.BLOCK_SIZE - O_TRANS)
58: / PhysicalRowId.SIZE;
59:
60: // slots we returned.
61: final PhysicalRowId[] slots = new PhysicalRowId[ELEMS_PER_PAGE];
62:
63: /**
64: * Constructs a data page view from the indicated block.
65: */
66: TranslationPage(BlockIo block) {
67: super (block);
68: }
69:
70: /**
71: * Factory method to create or return a data page for the
72: * indicated block.
73: */
74: static TranslationPage getTranslationPageView(BlockIo block) {
75: BlockView view = block.getView();
76: if (view != null && view instanceof TranslationPage)
77: return (TranslationPage) view;
78: else
79: return new TranslationPage(block);
80: }
81:
82: /** Returns the value of the indicated rowid on the page */
83: PhysicalRowId get(short offset) {
84: int slot = (offset - O_TRANS) / PhysicalRowId.SIZE;
85: if (slots[slot] == null)
86: slots[slot] = new PhysicalRowId(block, offset);
87: return slots[slot];
88: }
89: }
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