🚀 go-pugleaf

I have once again one of these questions dealing with the professional usage
of the advices of school-books about java.
So here it is:
I try to implement an application, that in the whole manipulates a certain
class A. That means every action in the gui is to manipulate a central
object OA.
I have implemented the manipulation of the object OA in an apllication that
can to be used on the command-line.

Now I would like to use swing-components. And here the problem comes up: In
which class (extended from a Swing component) do I now create the central
object?
Is it the "main" part, where I normally would only create the Jframe an call
"frame.show"; is it in the JFrame-constructor or is it in the content
Pane in the JPanel, where I also implement the Buttons, menues and so on?

And how do I make the central object known to all components of the GUI
(in other words: Where do I implement the call of the methods of  the class
to manipulate the object for example after pressing a Button?)

A long question, but as I said: My books only tell me where it is posible,
but not what is best.

Thanks
Thomas