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: PageCursor.java,v 1.1 2000/05/06 00:00:31 boisvert Exp $ 46 */ 47 48 package jdbm.recman; 49 50 import java.io.IOException; 51 52 /** 53 * This class provides a cursor that can follow lists of pages 54 * bi-directionally. 55 */ 56 final class PageCursor { 57 PageManager pageman; 58 long current; 59 short type; 60 61 /** 62 * Constructs a page cursor that starts at the indicated block. 63 */ 64 PageCursor(PageManager pageman, long current) { 65 this.pageman = pageman; 66 this.current = current; 67 } 68 69 /** 70 * Constructs a page cursor that starts at the first block 71 * of the indicated list. 72 */ 73 PageCursor(PageManager pageman, short type) throws IOException { 74 this.pageman = pageman; 75 this.type = type; 76 } 77 78 /** 79 * Returns the current value of the cursor. 80 */ 81 long getCurrent() throws IOException { 82 return current; 83 } 84 85 /** 86 * Returns the next value of the cursor 87 */ 88 long next() throws IOException { 89 if (current == 0) 90 current = pageman.getFirst(type); 91 else 92 current = pageman.getNext(current); 93 return current; 94 } 95 96 /** 97 * Returns the previous value of the cursor 98 */ 99 long prev() throws IOException { 100 current = pageman.getPrev(current); 101 return current; 102 } 103 }