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Java > Open Source Codes > com > quadcap > sql > file > Page


1 package com.quadcap.sql.file;
2
3 /* Copyright 1999 - 2003 Quadcap Software. All rights reserved.
4  *
5  * This software is distributed under the Quadcap Free Software License.
6  * This software may be used or modified for any purpose, personal or
7  * commercial. Open Source redistributions are permitted. Commercial
8  * redistribution of larger works derived from, or works which bundle
9  * this software requires a "Commercial Redistribution License"; see
10  * http://www.quadcap.com/purchase.
11  *
12  * Redistributions qualify as "Open Source" under one of the following terms:
13  *
14  * Redistributions are made at no charge beyond the reasonable cost of
15  * materials and delivery.
16  *
17  * Redistributions are accompanied by a copy of the Source Code or by an
18  * irrevocable offer to provide a copy of the Source Code for up to three
19  * years at the cost of materials and delivery. Such redistributions
20  * must allow further use, modification, and redistribution of the Source
21  * Code under substantially the same terms as this license.
22  *
23  * Redistributions of source code must retain the copyright notices as they
24  * appear in each source code file, these license terms, and the
25  * disclaimer/limitation of liability set forth as paragraph 6 below.
26  *
27  * Redistributions in binary form must reproduce this Copyright Notice,
28  * these license terms, and the disclaimer/limitation of liability set
29  * forth as paragraph 6 below, in the documentation and/or other materials
30  * provided with the distribution.
31  *
32  * The Software is provided on an "AS IS" basis. No warranty is
33  * provided that the Software is free of defects, or fit for a
34  * particular purpose.
35  *
36  * Limitation of Liability. Quadcap Software shall not be liable
37  * for any damages suffered by the Licensee or any third party resulting
38  * from use of the Software.
39  */
40
41 /**
42  * This interface models a page of data in a block file, either a main page
43  * (aka a Block) or a sub-page.
44  *
45  * @author Stan Bailes
46  */
47 public interface Page {
48     /**
49      * Return this page's block number
50      */
51     public long getPageNum();
52
53     /**
54      * An artifact of the Cacheable interface implemented by the Block
55      * class, we need to keep track of which objects are actually being
56      * used so unused objects can be flushed from the cache to make room
57      * for new objects. At some point, we can get rid of this in favor
58      * of weak references.
59      */
60     public void decrRefCount();
61
62     /**
63      * Read a range of bytes from the page.
64      *
65      * @param pos the offset in the page of the first byte to read
66      * @param pbuf the buffer into which the bytes are placed.
67      * @param offset the offset in <code>pbuf</code> where the first byte
68      * is placed.
69      * @param len the number of bytes to read
70      */
71     public int read(int pos, byte[] pbuf, int offset, int len);
72
73     /**
74      * Write a range of bytes to the page.
75      *
76      * @param pos the offset in the page of the first byte to write
77      * @param pbuf the buffer from which the bytes are obtained
78      * @param offset the offset in <code>pbuf</code> of the first byte
79      * to write
80      * @param len the number of bytes to write
81      */
82     public int write(int pos, byte[] pbuf, int offset, int len);
83
84     /**
85      * Read an integer (4-byte) value from the page.
86      *
87      * @param pos the offset in the page of the integer.
88      */
89     public int readInt(int pos);
90
91     /**
92      * Write an integer (4-byte) value to the page.
93      *
94      * @param pos the offset in the page of the integer.
95      * @param val the integer value to write.
96      */
97     public void writeInt(int pos, int val);
98
99     /**
100      * Read an long (8-byte) value from the page.
101      *
102      * @param pos the offset in the page of the long.
103      */
104     public long readLong(int pos);
105
106     /**
107      * Write an long (8-byte) value to the page.
108      *
109      * @param pos the offset in the page of the long.
110      * @param val the long value to write.
111      */
112     public void writeLong(int pos, long val);
113
114     /**
115      * Move the contents of the other page to this page, and zero out
116      * the other page.
117      */
118     public void takeData(Page p);
119
120     /**
121      * Zero this page
122      */
123     public void clear();
124     
125 }
126
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