I am making a Banking System, and this is the code for main.

import static java.lang.System.out;

public class BankSystem
    public static void main (String[] args)

        new username();

        new Password();

However, the problem is that both the username frame and password frame appears together. How do I make the username frame appear first, and after the username is authenticated?

Use a modal dialog.

there are two types of dialog box.modal and non-modal.
you can use modal dialogbox,means you have to give preference first to this modal dialog box then other dialog box is appeared.

so try with modal dialog box.