How to l get my java gui to popup?

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Java

I am trying to my gui to popup, I am building subway program where it supposed to simulate the event that create a subway sandwich which required u to create a gui and to which i have already but I want it to run/popup. I would like to see how it is but for some reason, I am missing something, so here the code that I used, can some one tell me what I am missing here. The codes below is what i have tried so far.




do I need to extend the jframe or something.

What I have tried:

public static void main(String[]args){


           JFrame frame = new JFrame("Test Frame");
           frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
           frame.setVisible(true);
           frame.setBackground(Color.green);

        }