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From "Shapira, Yoav" <>
Subject RE: instanceof drives me nuts!
Date Fri, 31 Oct 2003 14:43:44 GMT


>As I didn't build the project, I am not so familiar with it and I
>avoid to put some of the classes in several places (server, common,
>shared, WEB-INF of my apps....).

Don't do this, as it can lead to unpredictable classloading errors.
Keep everything you can in WEB-INF/lib, the rest in common/lib, but no
jar should be in both places.  And you probably don't need to put
anything at all of yours in the server classloader directories.
>Callback callback = getTheCallBackObject();
>if(callback instanceof ApplicationCallback) {
>        ((ApplicationCallback) callback).doSomething();
>When I debug this part, the expression 'callback instanceof
>ApplicationCallback' is true, nevertheless if I step once, the code in
>if block is not executed !!!

If the doSomething is not executed, how do you know if clause evaluates
to true?  From the debugger I suppose?

You can also try the other way around,
callback.getClass().isAssignableFrom(ApplicationCallback.class), to see
what would happen.

>Has anybody experienced this kind of weird behaviour?

Strange.  I think I've had that happen once or twice, but I can't recall
the solution ;(  

Yoav Shapira

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