001: /**
002: * JDBM LICENSE v1.00
003: *
004: * Redistribution and use of this software and associated documentation
005: * ("Software"), with or without modification, are permitted provided
006: * that the following conditions are met:
007: *
008: * 1. Redistributions of source code must retain copyright
009: * statements and notices. Redistributions must also contain a
010: * copy of this document.
011: *
012: * 2. Redistributions in binary form must reproduce the
013: * above copyright notice, this list of conditions and the
014: * following disclaimer in the documentation and/or other
015: * materials provided with the distribution.
016: *
017: * 3. The name "JDBM" must not be used to endorse or promote
018: * products derived from this Software without prior written
019: * permission of Cees de Groot. For written permission,
020: * please contact cg@cdegroot.com.
021: *
022: * 4. Products derived from this Software may not be called "JDBM"
023: * nor may "JDBM" appear in their names without prior written
024: * permission of Cees de Groot.
025: *
026: * 5. Due credit should be given to the JDBM Project
027: * (http://jdbm.sourceforge.net/).
028: *
029: * THIS SOFTWARE IS PROVIDED BY THE JDBM PROJECT AND CONTRIBUTORS
030: * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
031: * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
032: * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
033: * CEES DE GROOT OR ANY CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
034: * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
035: * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
036: * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
037: * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
038: * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
039: * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
040: * OF THE POSSIBILITY OF SUCH DAMAGE.
041: *
042: * Copyright 2000 (C) Cees de Groot. All Rights Reserved.
043: * Contributions are Copyright (C) 2000 by their associated contributors.
044: *
045: * $Id: PageCursor.java,v 1.1 2000/05/06 00:00:31 boisvert Exp $
046: */package jdbm.recman;
047:
048: import java.io.IOException;
049:
050: /**
051: * This class provides a cursor that can follow lists of pages
052: * bi-directionally.
053: */
054: final class PageCursor {
055: PageManager pageman;
056: long current;
057: short type;
058:
059: /**
060: * Constructs a page cursor that starts at the indicated block.
061: */
062: PageCursor(PageManager pageman, long current) {
063: this .pageman = pageman;
064: this .current = current;
065: }
066:
067: /**
068: * Constructs a page cursor that starts at the first block
069: * of the indicated list.
070: */
071: PageCursor(PageManager pageman, short type) throws IOException {
072: this .pageman = pageman;
073: this .type = type;
074: }
075:
076: /**
077: * Returns the current value of the cursor.
078: */
079: long getCurrent() throws IOException {
080: return current;
081: }
082:
083: /**
084: * Returns the next value of the cursor
085: */
086: long next() throws IOException {
087: if (current == 0)
088: current = pageman.getFirst(type);
089: else
090: current = pageman.getNext(current);
091: return current;
092: }
093:
094: /**
095: * Returns the previous value of the cursor
096: */
097: long prev() throws IOException {
098: current = pageman.getPrev(current);
099: return current;
100: }
101: }
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