How to paint an invisible JFrame elsewhere?

Question

I want to paint the contents of a JFrame onto another frame. Currently, I only get it to work if the JFrame is visible.
Is there a way to paint a hidden JFrame?

Addi

Answer 1

1) you have to use proper LayoutManager, not setSize() or setBounds()

2) if is there null LayoutManager used then Container returns any size after setVisible(true);

3) if is there used proper LayoutManager, then Container return its Size after call pack();, in other hands this container couldn't be visible on the screen ( meaning setVisible(true); )

4) JComponents must to returns PrefferedSize for example

Answer 2

Hint 1: JFrame's setDefaultLookAndFeelDecorated(false)/setUndecorated(true) might be of use for a window without caption and borders;

Hint 2: as setGlassPane/setLayeredPane/setOpaque(false) might be of use for a second "layer".

Answer 3

I want to get the graphical contents of a frame without having to make the frame visible for the user

The Screen Image class should help. Although I think it will only work for the "content pane" of the frame and not the entire frame (with the title bar and borders) unless you use a decorated frame.