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Java > Open Source Codes > com > mckoi > database > TNullType


1 /**
2  * com.mckoi.database.TNullType 02 Aug 2002
3  *
4  * Mckoi SQL Database ( http://www.mckoi.com/database )
5  * Copyright (C) 2000, 2001, 2002 Diehl and Associates, Inc.
6  *
7  * This program is free software; you can redistribute it and/or
8  * modify it under the terms of the GNU General Public License
9  * Version 2 as published by the Free Software Foundation.
10  *
11  * This program is distributed in the hope that it will be useful,
12  * but WITHOUT ANY WARRANTY; without even the implied warranty of
13  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14  * GNU General Public License Version 2 for more details.
15  *
16  * You should have received a copy of the GNU General Public License
17  * Version 2 along with this program; if not, write to the Free Software
18  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
19  *
20  * Change Log:
21  *
22  *
23  */
24
25 package com.mckoi.database;
26
27 import com.mckoi.database.global.SQLTypes;
28
29 /**
30  * An implementation of TType that represents a NULL type. A Null type is
31  * an object that can't be anything else except null.
32  *
33  * @author Tobias Downer
34  */
35
36 public class TNullType extends TType {
37
38   static final long serialVersionUID = -271824967935043427L;
39
40   /**
41    * Constructs the type.
42    */
43   public TNullType() {
44     // There is no SQL type for a query plan node so we make one up here
45 super(SQLTypes.NULL);
46   }
47
48   public boolean comparableTypes(TType type) {
49     return (type instanceof TNullType);
50   }
51   
52   public int compareObs(Object JavaDoc ob1, Object JavaDoc ob2) {
53     // It's illegal to compare NULL types with this method so we throw an
54 // exception here (see method specification).
55 throw new Error JavaDoc("compareObs can not compare NULL types.");
56   }
57   
58   public int calculateApproximateMemoryUse(Object JavaDoc ob) {
59     return 16;
60   }
61   
62   public Class JavaDoc javaClass() {
63     return Object JavaDoc.class;
64   }
65
66 }
67
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