How to connect JAVA code to Graphics?

Question

I've written a card game in Java, but I can play it only in Command Line.
On the other hand, I know how to draw with swing in Java. But the question is here.
Shall I somehow connect my game to Graphics or write entirely new code all with GUI?
I really don't know how to make my existing game visible for users. Although, I know about JAVA Graphics. I can write separate codes in Graphics only.
I just don't know how simple codes and Graphics combine together.
Where can I find info about this kind of philosophy?