KickJava   Java API By Example, From Geeks To Geeks.

Java > Open Source Codes > com > quadcap > sql > PredicateCursor


1 package com.quadcap.sql;
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 import java.util.Vector JavaDoc;
42
43 import java.sql.SQLException JavaDoc;
44
45 import com.quadcap.sql.types.Value;
46 import com.quadcap.sql.types.ValueBoolean;
47 import com.quadcap.sql.types.ValueUnknown;
48
49 import com.quadcap.util.Debug;
50
51 /**
52  * Cursor for <b>WHERE</b> predicates.
53  *
54  * @author Stan Bailes
55  */
56 public class PredicateCursor extends FilterCursor {
57     Expression predicate = null;
58     Row row = null;
59
60     /**
61      * A PredicateCursor is a kind of FilterCursor which only returns
62      * rows which match a predicate
63      */
64     public PredicateCursor(Session session, Cursor cursor,
65                Expression predicate) throws SQLException JavaDoc {
66     super(session, cursor);
67     this.predicate = predicate;
68     }
69
70     /**
71      * Return the current cursor row
72      */
73     public Row getRow() throws SQLException JavaDoc {
74     return row;
75     }
76
77     /**
78      * Cursor.next() Advance the cursor and return 'true' if the cursor
79      * advances past a valid item. This item becomes the current row.
80      */
81     public boolean next() throws SQLException JavaDoc {
82     row = null;
83     while (row == null && cursor.next()) {
84         Value val = predicate.getValue(session, cursor);
85             //Debug.println("[" + predicate + "] on " + cursor.getRow() + " " +
86 // (outer == null ? "{}" : outer.getRow().toString()) + " = " + val);
87 if (Value.isTrue(val)) {
88                 row = cursor.getRow();
89             }
90     }
91     return row != null;
92     }
93
94     /**
95      * Cursor.next() Retreat the cursor and return 'true' if the cursor
96      * moves past a valid item. This item becomes the current row.
97      */
98     public boolean prev() throws SQLException JavaDoc {
99     row = null;
100     while (row == null && cursor.prev()) {
101         Value val = predicate.getValue(session, cursor);
102             if (Value.isTrue(val)) {
103                 row = cursor.getRow();
104             }
105     }
106     return row != null;
107     }
108
109     /**
110      * Position the cursor to the specified absolute row. The first row
111      * is row '1', and the last row is '-1', as in JDBC.
112      */
113     public boolean absolute(int row) throws SQLException JavaDoc {
114         if (row > 0) {
115             beforeFirst();
116             while (row-- > 0) if (!next()) return false;
117         } else {
118             afterLast();
119             while (row++ < 0) if (!prev()) return false;
120         }
121         return true;
122     }
123
124     
125     //#ifdef DEBUG
126 public String JavaDoc toString() {
127         return "PredicateCursor: " + super.toString();
128     }
129     //#endif
130
131 }
132
Popular Tags