🚀 go-pugleaf

Richard Hawkes <rhawkes@nbtel.nb.ca> wrote:

> Hi,  I am writing a applet with JBuilder 2.  My program runs a thread
> that keeps checking a screen for a field of text to appear.  When this
> happens I want to trigger and event back in the main program.
>     I figured I could use the same functionality that a button event
> uses.  I would throw some kind of event from the Thread, and then the
> Main program would have a listener that would be activated, and then it
> would run some code.

There really is not anything called a "main program" in a Java 
program.

There is the thread that runs the main() method, but in most 
interactive Java programs that thread terminates shortly after 
you start your program.  It usually creates a frame and makes it 
visible, and then exists.  As a side effect of making the frame 
visible, the AWT creates several other threads that keep your 
program alive.

Anything you throw must be derived from Throwable - this includes 
Exceptions and Errors, but not any event class.  Also, it is not 
possible to throw a Throwable from one thread to another.  When 
you throw a Throwable, it is passed back through the call chain 
of the thread they are thrown from.  If nothing catches them then 
the thread dies.  So this approach will not work.

One of the threads created when you make your frame visible is 
the AWT event thread.  It monitors the event queue, removing 
events from the queue when one is available, and dispatches them 
to the appropriate component.  One approach you might try is to 
post an event to the AWT event queue.  I have never done it, but 
it may work.

Why is it that you want the code to run in a different thread 
than the one that detects the condition?  And if this is really 
necessary, can you create another thread to process the "event"?

-- 
Regards,

John P. McGrath
<mcgrath@enter.net>
<jpm@nscs.fast.net>