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Java > Open Source Codes > smallsql > database > ExpressionFunction


1 /* =============================================================
2  * SmallSQL : a free Java DBMS library for the Java(tm) platform
3  * =============================================================
4  *
5  * (C) Copyright 2004-2006, by Volker Berlin.
6  *
7  * Project Info: http://www.smallsql.de/
8  *
9  * This library is free software; you can redistribute it and/or modify it
10  * under the terms of the GNU Lesser General Public License as published by
11  * the Free Software Foundation; either version 2.1 of the License, or
12  * (at your option) any later version.
13  *
14  * This library is distributed in the hope that it will be useful, but
15  * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
16  * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
17  * License for more details.
18  *
19  * You should have received a copy of the GNU Lesser General Public
20  * License along with this library; if not, write to the Free Software
21  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
22  * USA.
23  *
24  * [Java is a trademark or registered trademark of Sun Microsystems, Inc.
25  * in the United States and other countries.]
26  *
27  * ---------------
28  * ExpressionFunction.java
29  * ---------------
30  * Author: Volker Berlin
31  *
32  */
33 package smallsql.database;
34
35 import java.sql.*;
36
37
38 /**
39  * This is the base class for all functions. To add a new fuction you need<p>
40  * 1.) Add a new constant to the class SQLTokenizer.<p>
41  * 2.) Add a mapping of the function name keyword to the function constant in the class SQLTokenizer.<p>
42  * 3.) Extends a class from ExpressionFunction and implemets the function logic.<p>
43  * 4.) Add a case to the switch in SQLParser.function().<p>
44  */
45
46 abstract class ExpressionFunction extends Expression {
47
48     Expression param1;
49     Expression param2;
50     Expression param3;
51     Expression param4;
52
53     ExpressionFunction(){
54         super(FUNCTION);
55     }
56
57     // setzt die Funktionsnummer z.B. bei abs(5) --> SQLTokenizer.ABS
58 abstract int getFunction();
59
60     byte[] getBytes() throws Exception JavaDoc{
61         return ExpressionValue.getBytes(getObject(), getDataType());
62     }
63
64     void setParams( Expression[] params ){
65         super.setParams( params );
66         if(params.length >0) param1 = params[0] ;
67         if(params.length >1) param2 = params[1] ;
68         if(params.length >2) param3 = params[2] ;
69         if(params.length >3) param4 = params[3] ;
70     }
71
72     final void setParamAt( Expression param, int idx){
73         switch(idx){
74             case 0:
75                 param1 = param;
76                 break;
77             case 1:
78                 param2 = param;
79                 break;
80             case 2:
81                 param3 = param;
82                 break;
83             case 3:
84                 param4 = param;
85                 break;
86         }
87         super.setParamAt( param, idx );
88     }
89     
90
91     /**
92      * Is used in GroupResult.
93      */
94     public boolean equals(Object JavaDoc expr){
95         if(!super.equals(expr)) return false;
96         if(!(expr instanceof ExpressionFunction)) return false;
97         return ((ExpressionFunction)expr).getFunction() == getFunction();
98     }
99
100     
101     /**
102      * Create a SQLException that the current function does not support the specific data type.
103      * @param dataType A data type const from SQLTokenizer.
104      */
105     SQLException createUnspportedDataType( int dataType ){
106         return Utils.createSQLException("Unsupported data type '" +
107                     SQLTokenizer.getKeyWord(dataType) +
108                     "' for function " +
109                     SQLTokenizer.getKeyWord(getFunction()) );
110     }
111
112     /**
113      * Create a SQLException that the current function can not convert the specific data type.
114      * @param dataType A data type const from SQLTokenizer.
115      */
116     SQLException createUnspportedConversion( int dataType ){
117         return Utils.createSQLException("Unsupported conversion to data type '" +
118                     SQLTokenizer.getKeyWord(dataType) +
119                     "' for function " +
120                     SQLTokenizer.getKeyWord(getFunction()) );
121     }
122
123
124
125 }
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