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 2000,2003 (C) Exoffice Technologies Inc. All Rights Reserved.
42 */
43
44 package org.exolab.jms.selector;
45
46 import javax.jms.Message;
47
48
49 /***
50 * This class implements an 'is' expression.
51 * This is an expression that returns true if a identifier's value is null.
52 *
53 * @version $Revision: 1.1 $ $Date: 2004/11/26 01:50:44 $
54 * @author <a href="mailto:tma@netspace.net.au">Tim Anderson</a>
55 * @see Identifier
56 * @see IdentifierExpression
57 */
58 class IsExpression extends IdentifierExpression {
59
60 /***
61 * Construct a new <code>IsExpression</code>
62 *
63 * @param ident the identifier
64 */
65 public IsExpression(final Identifier ident) {
66 super(ident);
67 }
68
69 /***
70 * Evaluate the expression
71 *
72 * @param msg the message to use to obtain any header identifier and
73 * property values
74 * @return the evaluated result, or <code>null</code> if the value of the
75 * expression is unknown
76 * @throws TypeMismatchException if the expression tries to evaluate
77 * mismatched types.
78 */
79 public final SObject evaluate(final Message msg)
80 throws TypeMismatchException {
81 SBool result = null;
82 SObject value = identifier().evaluate(msg);
83 if (value == null) {
84 result = SBool.TRUE;
85 } else {
86 result = SBool.FALSE;
87 }
88 return result;
89 }
90
91 /***
92 * Return a string representation of this expression.
93 *
94 * @return a string representation of this expression
95 */
96 public final String toString() {
97 return "(" + identifier().toString() + " is null)";
98 }
99 }