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A null layout is usually a very bad idea. It doesnt scale well, actually, it doesnt scale at all. And you have so much work to position all elements by hand.
Just study the different layouts and...

The problem is you make your frame visible and afterwards you keep adding components to it.
Once you make a frame visible the frame will then arrange its contents and paint itself. If you change...

Probably because you did something wrong in your code.
But we cant really tell because we dont know your code.

When you post your code make sure to put it inside [code] brackets.