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Java > Open Source Codes > org > mr > api > jms > selector > syntax > IsExpression


1 /*
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16  * The Original Code is "MantaRay" (TM).
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46 package org.mr.api.jms.selector.syntax;
47
48 import javax.jms.Message JavaDoc;
49
50
51 /**
52  * This class implements an 'is' expression.
53  * This is an expression that returns true if a identifier's value is null.
54  *
55  */

56 class IsExpression extends IdentifierExpression {
57
58     /**
59      * Construct a new IsExpression
60      *
61      * @param ident the identifier
62      */

63     public IsExpression(final Identifier ident) {
64         super(ident);
65     }//IsExpression
66

67     
68     /**
69      * Evaluate the expression
70      *
71      * @param msg the message to use to obtain any header identifier and property values
72      * @return the evaluated result, or null if the value of the expression is unknown
73      * @throws TypeMismatchException if the expression tries to evaluate mismatched types.
74      */

75     public final MantaObject evaluate(final Message JavaDoc msg) throws TypeMismatchException {
76         MantaBoolean result = null;
77         MantaObject value = identifier().evaluate(msg);
78
79         if (value == null) {
80             result = MantaBoolean.TRUE;
81         }//if
82
else {
83             result = MantaBoolean.FALSE;
84         }//else
85
return result;
86     }//evaluate
87

88
89     /**
90      * Return a string representation of this expression.
91      *
92      * @return a string representation of this expression
93      */

94     public final String JavaDoc toString() {
95         return "(" + identifier().toString() + " is null)";
96     }//toString
97
}//IsExpression
98
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