🚀 go-pugleaf

I'm new to NeXT and Objective C. These might be stupid questions but...
Anyway. I'm studying this famous "Plotter" program, I have couple 
things that I don't understand.

1) What is Category?
   In the PlotView.h listing, 

    @interface Object(PlotViewDelegate)
    - plotView:sender providePoints:(NXStream **)stream;
    - plotView:sender pointDidChange:(NXPoint *)aPoint;
    @end

   I can't find any reference of Category "PlotViewDelegate" anywhere 
in the program. What is it? 
   Do the codes mean adding two more methods to class Object?
   Does that mean all Class' derived from Object will have the
two new methods?
   The listing also has "setDelegate" defined. But in PlotController,
this "setDelegate" is not invoked at all. Therefore, "delegate"
remains uninitialized, right? Then how does PlotView know PlotController
is the delegate?

   In "PlotController.h", theScrollView and thePlotView are defined
as id. In method appDidInit,

   inputText = [theScrollView docView];
   ...
   [[thePlotView window] makeKeyAndOrderFront];

   How can theScrollView be used as a class to define inputText? Don't
you initialize theScrollView first? like 
   
   ScrollView *theScrollView = [ScrollView new];
   inputText = [theScrollView docView];

Same question about PlotView.  


Any comments are welcome.



Regards,
Hayward
Internet: hlam@bnr.ca
********************************************************************
I only speak for my evil twin brother.