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That is something that a good design would isolate to one variable vs having hard coded magic numbers hidden in the code.
Is that what the 30 that I see here and there is used for?

I only have XP so you'll have to wait for someone with another OS.

I don't know how putting the paint method in a JPanel would cause you problems.
What do the problems look like? What works...

The changes were to put the paint method in a JPanel class. That's all I did.

Replace the definition of p,
insert the class MyJPanel ... {
and the ending }
and change paint to paintComponent.

Some suggested code changes to make the drawing a bit smoother:

MyJPanel p = new MyJPanel(); // Use your own class
...
class MyJPanel extends JPanel { // Add this line before paint()
...