Error with logic or repaint/revalidate Java JFrame

Question

What I am trying to do is this, when I enter the details it will validate if the textFiled is empty when a button is pressed, if it is empty it will display a message saying tha

Answer 1

1. have look at DocumentListener,

2. on start_up to enable only first JTextField, if any (up to you) character was typed into first JTextField, then enable second JTextField, and so on...,

3. if you want to filtering, change or replace output came from keyboard the to use DocumentFilter

4. change background for example to Color.red (from DocumentListeners events), in the case that one of JTextFields contains incorect lenght, data e.g.

5. agree with HFOE about LayoutManagers