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


1 /**
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3  * ("Software"), with or without modification, are permitted provided
4  * that the following conditions are met:
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8  * copy of this document.
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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.
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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
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26  * (http://www.exolab.org/).
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28  * THIS SOFTWARE IS PROVIDED BY EXOFFICE TECHNOLOGIES AND CONTRIBUTORS
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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 implements a unary minus operator.
51  *
52  * @version $Revision: 1.1 $ $Date: 2004/11/26 01:50:45 $
53  * @author <a HREF="mailto:tma@netspace.net.au">Tim Anderson</a>
54  * @see Expression
55  * @see SNumber
56  * @see UnaryOperator
57  */
58 class UnaryMinus extends UnaryOperator {
59
60     /**
61      * The expression context, for error reporting purposes
62      */
63     private static final String JavaDoc CONTEXT = "unary minus";
64
65     /**
66      * Helper for -1
67      */
68     private static final SLong MINUS1 = new SLong(-1);
69
70     /**
71      * Construct a new <code>UnaryMinus</code> operator
72      *
73      * @param operand the operand
74      */
75     public UnaryMinus(final Expression operand) {
76         super("-", operand);
77     }
78
79     /**
80      * Evaluate the expression
81      *
82      * @param msg the message to evaluate this expression against
83      * @return the result of expression
84      * @throws TypeMismatchException if the operand doesn't evaluate to
85      * a numeric or null
86      */
87     public final SObject evaluate(final Message JavaDoc msg)
88         throws TypeMismatchException {
89         SObject result = null;
90         SNumber value = TypeCaster.castToNumber(operand().evaluate(msg),
91                                                 CONTEXT);
92         if (value != null) {
93             result = value.multiply(MINUS1);
94         }
95         return result;
96     }
97
98 } //-- UnaryMinus
99
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