How do I extend default joomla class / function?

Question

I want to extend the submit file function in Joomla in an extension I'm making to custom handle files, how do I do that? Can I get some code samples please.

I've been told to extend them in the Model, but whenever I try to extend anything I get an error, even if I have an empty function that just says "..extends xxxx{}.

Answer 1

see below url and read :-

http://docs.joomla.org/How_Joomla_pieces_work_together

Or

class <name>Controller extends JController
{

}