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Java > Open Source Codes > org > xquark > extractor > algebra > LitNull


1 /*
2  * This file belongs to the XQuark distribution.
3  * Copyright (C) 2003 Universite de Versailles Saint-Quentin.
4  *
5  * This program is free software; you can redistribute it and/or
6  * modify it under the terms of the GNU Lesser General Public
7  * License as published by the Free Software Foundation; either
8  * version 2.1 of the License, or (at your option) any later version.
9  *
10  * This program is distributed in the hope that it will be useful,
11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13  * Lesser General Public License for more details.
14  *
15  * You should have received a copy of the GNU Lesser General Public
16  * License along with this program; if not, write to the Free Software
17  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307.
18  * You can also get it at http://www.gnu.org/licenses/lgpl.html
19  *
20  * For more information on this software, see http://www.xquark.org.
21  */
22
23 package org.xquark.extractor.algebra;
24
25 import java.util.Map JavaDoc;
26
27 import org.xquark.extractor.common.SqlWrapperException;
28 import org.xquark.extractor.sql.SqlExpression;
29
30 public final class LitNull extends Literal {
31
32     private static final String JavaDoc RCSRevision = "$Revision: 1.4 $";
33     private static final String JavaDoc RCSName = "$Name: $";
34
35
36     public LitNull() {
37     }
38
39     synchronized Object JavaDoc clone(Map JavaDoc clonedExprs) throws CloneNotSupportedException JavaDoc
40     {
41         //Trace.enter(this, "clone(Map clonedExprs)");
42
43         LitNull retVal = (LitNull)super.clone(clonedExprs);
44
45         clonedExprs.put(this, retVal);
46         //Trace.exit(this, "clone(Map clonedExprs)");
47 return retVal;
48     }
49
50     public SqlExpression accept (GenSqlVisitor visitor) throws SqlWrapperException
51     {
52         return visitor.visit(this);
53     }
54
55     public void accept (AlgebraVisitor visitor) throws SqlWrapperException
56     {
57         visitor.visit(this);
58     }
59
60     /**
61      * @see Expression#deepEquals(Object)
62      */
63     public boolean deepEquals(Object JavaDoc o)
64     {
65         return (o instanceof LitNull);
66     }
67 }
68
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