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Java Event Scripts
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Java Event Scripts
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About:
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A callback script is evaluated when a Java object fires an event. In most cases,
the script does not need to return a value to the caller. There are some cases
where a return value is needed. In such a case, the event method corresponding
to the event has a <B>non-void</B> return type. The callback script should
use the <B>return</B> command to return the desired value or Java object.

<P>

When a Java object fires an event, it may expect the callback script
to throw an exception to indicate certain conditions. This can be done
using the <B>java::throw</B> command. For example: the
<B>vetoableChange</B> event requires the callback script to throw a
<B>java.beans.PropertyVetoException</B> if the script deems the new value of a
property unaccecptable, as in the following code fragment:
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<CODE>
<PRE>
java::bind $b vetoableChange {
    if {[java::event propertyName] == &quot;size&quot;} {
        if {[java::event newValue] &gt; 10} {
            java::throw [java::new java.beans.PropertyVetoException \
                &quot;value too large&quot; [java::event]]
        }
    }
}
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The callback script can throw any unchecked exception object (e.g.,
instances of <B>java.lang.Error</B> or
<B>java.lang.RuntimeException</B>.) The callback script can also throw
any checked exception allowed by the signature of the event method.
<P>
If the callback script throws a checked exception which is not allowed
for the event, a Tcl background error is generated. If the callback
script is expected to return a value, an undefined value is returned
to the Java object.
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<A HREF="../license.html">Copyright</A> &#169; 1997-1998 Sun Microsystems, Inc.
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