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 }