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 }