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java.lang.ClassCastException: com/ms/wfc/app/Timer$TimerProc from a Window.callback

Posted on 2008-10-29
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Last Modified: 2013-12-16
Does anybody know what kind of windows callbacks throws the following exception (see the callstack below).
The callstack contains a ListView.wndProc call, so it's possible that it's a ListView specific question.
The application was built with Microsoft Visual J++ 6.0.

java.lang.ClassCastException: com/ms/wfc/app/Timer$TimerProc
            at com/ms/wfc/app/Window.fromHandle
            at com/ms/wfc/ui/Control.fromHandle
            at com/ms/wfc/ui/Control.reflectMessage
            at com/ms/wfc/ui/Control.wmNotify
            at com/ms/wfc/ui/Control.wndProc
            at com/ms/wfc/ui/Form.wndProc
            at com/ms/wfc/app/Application$ParkingForm.wndProc
            at com/ms/wfc/ui/Control$ControlWindow.wndProc
            at com/ms/wfc/app/Window.callback
            at com/ms/wfc/win32/Windows.CallWindowProc
            at com/ms/wfc/app/Window.defWndProc
            at com/ms/wfc/ui/Control$ControlWindow.defWndProc
            at com/ms/wfc/ui/Control.defWndProc
            at com/ms/wfc/ui/Control.wmPaint
            at com/ms/wfc/ui/Control.wndProc
            at com/ms/wfc/ui/ListView.wndProc
            at com/ms/wfc/ui/Control$ControlWindow.wndProc
            at com/ms/wfc/app/Window.callback
            at com/ms/wfc/win32/Windows.DispatchMessage
            at com/ms/wfc/app/Application$ThreadContext.runMessageLoop
            at com/ms/wfc/app/Application.run
            at Form2.main

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Question by:tctdev
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Expert Comment

by:Kevin Cross
ID: 22835789
Please show snippet of code associated to this error message if it told you or if your main() method is fairly small just paste in the whole thing.

java.lang.ClassCastException ==> Usually occurs when you are setting one object equal to another object and the explicit or implicit casting cannot be done.  Examples would be you can cast a sub class to a parent class, but not the other way around.   Things of that nature.

Usually you will see this in code as:
Type2 t2 = (Type2) t1;

Kev
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Author Comment

by:tctdev
ID: 22840994
mwvisa1:
I can't reproduce the problem, it's very ad hoc. My source is not too little (~2 MB) and the main() method is very simple (see below)

I think the conflict must be between the followings:
- Timer (I use ~30 timer, but I use these very rarely, the most is disabled)
- com.ms.wfc.app.MethodInvoker: to make changes on the Controls requested from a thread (not from the main thread)
- ListView callback (it appears on the callstack lista)

I know the ClassCastException but it's thrown by an automatic windows callback, not by my code. I never use the
Timer.TimerProc class, and I never cast it.

jkr:
I think this problem is closer to mfc than standard java programming (because of microsoft java using and windows callbacks)

I hope, that somebody met something like similar.
Thanks!

	public static void main(String args[])
	{
		Form2.params = args;
		Application.OLERequired();
		Application.run(new Form2());
	}

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Expert Comment

by:Kevin Cross
ID: 22841093
This could be a threading issue which is why it happens haphazardly as it depends on occurrence of conflict.
// this statement makes me think you are setting a static variable
// what happens if another call comes in and changes this mid stream
// is params defined as String[] like args is
Form2.params = args; 
 
Application.OLERequired();
 
// you then call a new form instance here
// hopefully this form uses the static params passed in above
Application.run(new Form2());
 
 
/********************/
// could this work for you
Form2 f = new Form2(); // or Form2(args); 
f.params = args;
Application.OLERequired();
Application.run(f);

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Author Comment

by:tctdev
ID: 22841379
The Form2 object is created only in the main(), has only one instance.
I don't know what another call could come in, but I'm going to give it a try.

I will inform you within few days.

Thanx.
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Author Comment

by:tctdev
ID: 22874914
Not work. The exception and the callstack are the same.
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Assisted Solution

by:Kevin Cross
Kevin Cross earned 100 total points
ID: 22876200
tcdev,

I am not sure what is causing this right now.  Maybe you are right that you need a MFC officianado. :)

Will keep monitoring question and thinking of possible causes/solutions, though.

Kev
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Author Comment

by:tctdev
ID: 22974647
I'll remove all the timers ...  Come back soon ...
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Accepted Solution

by:
tctdev earned 0 total points
ID: 23043589
Replacing all the timers with my own timer class instances gives me the solution. My timer class is consist of a simple thread and MethodInvoker calls at all ticks.
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