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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  }