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


1 /**
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3  * ("Software"), with or without modification, are permitted provided
4  * that the following conditions are met:
5  *
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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.
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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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25  * 5. Due credit should be given to the Exolab Project
26  * (http://www.exolab.org/).
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28  * THIS SOFTWARE IS PROVIDED BY EXOFFICE TECHNOLOGIES AND CONTRIBUTORS
29  * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
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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 (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 boolean binary
51  * operators. These return a boolean 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:tima@intalio.com">Tim Anderson</a>
56  * @see Expression
57  * @see SBool
58  */
59 abstract class LogicalOperator extends BinaryOperator {
60
61     /**
62      * Construct a new <code>LogicalOperator</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 LogicalOperator(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 use to obtain any header identifier and
77      * property values
78      * @return the evaluated result, or <code>null</code> if the value of the
79      * expression is unknown
80      * @throws TypeMismatchException if the expression tries to evaluate
81      * mismatched types.
82      */
83     public SObject evaluate(final Message JavaDoc msg) throws TypeMismatchException {
84         SBool result = null;
85
86         SObject lhs = left().evaluate(msg);
87         if (lhs != null) {
88             SObject rhs = right().evaluate(msg);
89             if (rhs != null) {
90                 checkTypes(lhs.type(), rhs.type());
91                 result = evaluate(lhs, rhs);
92             }
93         }
94         return result;
95     }
96
97     /**
98      * Perform a logical comparison
99      *
100      * @param lhs the left hand side of the expression
101      * @param rhs the right hand side of the expression
102      * @return the evaluated result
103      */
104     protected SBool evaluate(final SObject lhs, final SObject rhs) {
105         return null;
106     }
107
108     /**
109      * Verifies that the types of expression can be verified.
110      *
111      * @param lhs the left hand side of the expression
112      * @param rhs the right hand side of the expression
113      * @throws TypeMismatchException if the types cannot be compared
114      */
115     protected void checkTypes(final Type lhs, final Type rhs)
116         throws TypeMismatchException {
117         if (lhs != rhs) {
118             StringBuffer JavaDoc msg = new StringBuffer JavaDoc();
119             msg.append("expecting a ");
120             msg.append(lhs);
121             msg.append(" expression for operator ");
122             msg.append(operator());
123             msg.append(", found a ");
124             msg.append(rhs);
125             throw new TypeMismatchException(msg.toString());
126         }
127     }
128
129 } //-- LogicalOperator
130
131
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