Manipulating components of a seperate GUI Class

It's been a while since I've used Java and I'm getting back into it. I was wondering if someone could explain how I can manipulate components in a window I've used a different class to create.

I created a public class called Dashboard_GUI, I want another class (Dashboard_Main) to instantiate a Dashboard_GUI object and I want the Main class to be able to change the GUI's components and add to it's tables etc. I don't remember the name of the term I need to research whether it's abstract, implements, extends or what. Or maybe it's just a matter of putting the methods to manipulate it in the GUI class and call them. Just want to make sure I'm going to head in the right direction.

I know there are a lot of other things involved, specifically variable declarations and such but rather than getting into all of that I want to research it myself and ask further questions later since I learn better that way.

What you want to do is basically clean OOPs programming techniques. If you want an outside program to change your class's state, give the class a public method to do so. There's no difference here for GUI programming.