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Java > Open Source Codes > org > exolab > jms > selector > MathOperator


1 /**
2  * Redistribution and use of this software and associated documentation
3  * ("Software"), with or without modification, are permitted provided
4  * that the following conditions are met:
5  *
6  * 1. Redistributions of source code must retain copyright
7  * statements and notices. Redistributions must also contain a
8  * copy of this document.
9  *
10  * 2. Redistributions in binary form must reproduce the
11  * above copyright notice, this list of conditions and the
12  * following disclaimer in the documentation and/or other
13  * materials provided with the distribution.
14  *
15  * 3. The name "Exolab" must not be used to endorse or promote
16  * products derived from this Software without prior written
17  * permission of Exoffice Technologies. For written permission,
18  * please contact info@exolab.org.
19  *
20  * 4. Products derived from this Software may not be called "Exolab"
21  * nor may "Exolab" appear in their names without prior written
22  * permission of Exoffice Technologies. Exolab is a registered
23  * trademark of Exoffice Technologies.
24  *
25  * 5. Due credit should be given to the Exolab Project
26  * (http://www.exolab.org/).
27  *
28  * THIS SOFTWARE IS PROVIDED BY EXOFFICE TECHNOLOGIES AND CONTRIBUTORS
29  * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
30  * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
31  * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
32  * EXOFFICE TECHNOLOGIES OR ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
33  * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
34  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
35  * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
36  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
37  * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
38  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
39  * OF THE POSSIBILITY OF SUCH DAMAGE.
40  *
41  * Copyright 2000-2001,2003 (C) Exoffice Technologies Inc. All Rights Reserved.
42  */
43
44 package org.exolab.jms.selector;
45
46 import javax.jms.Message JavaDoc;
47
48
49 /**
50  * This class is the base class for all expressions that are numeric binary
51  * operators. These return a numeric result when evaluated, or null
52  * if the result is undefined.
53  *
54  * @version $Revision: 1.1 $ $Date: 2004/11/26 01:50:44 $
55  * @author <a HREF="mailto:tma@netspace.net.au">Tim Anderson</a>
56  * @see Expression
57  * @see SNumber
58  */
59 abstract class MathOperator extends BinaryOperator {
60
61     /**
62      * Construct a new <code>MathOperator</code>
63      *
64      * @param operator the operator
65      * @param lhs the left hand side of the expression
66      * @param rhs the right hand side of the expression
67      */
68     protected MathOperator(final String JavaDoc operator, final Expression lhs,
69                            final Expression rhs) {
70         super(operator, lhs, rhs);
71     }
72
73     /**
74      * Evaluate the expression
75      *
76      * @param msg the message to evaluate this expression against
77      * @return the result of expression
78      * @throws TypeMismatchException if the result of the left or right
79      * hand expressions are not numeric
80      */
81     public final SObject evaluate(final Message JavaDoc msg)
82         throws TypeMismatchException {
83
84         SNumber result = null;
85         SNumber lhs = TypeCaster.castToNumber(left().evaluate(msg), context());
86         if (lhs != null) {
87             SNumber rhs = TypeCaster.castToNumber(right().evaluate(msg),
88                 context());
89             if (rhs != null) {
90                 result = evaluate(lhs, rhs);
91             }
92         }
93         return result;
94     }
95
96     /**
97      * Evaluate the expression
98      *
99      * @param lhs the left hand side of the expression
100      * @param rhs the right hand side of the expression
101      * @return the result of expression
102      */
103     protected abstract SNumber evaluate(final SNumber lhs, final SNumber rhs);
104
105     /**
106      * The context of the expression, for error reporting purposes
107      *
108      * @return the context of the expression
109      */
110     private final String JavaDoc context() {
111         return "operator " + operator();
112     }
113
114 } //-- MathOperator
115
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