Question

I search for a method, which gets called if the jpanel is shown on the display, because i have to fetch the real size of the panel.

Any suggestions?

Answer 1

Have you tried adding a ComponentListener to the JPanel? That would be where I would start with my code in the componentShown(...) method. For this to work, I think that you must call setVisible(true) on the JPanel after adding it to the display.

The other option is to simply query its size after calling pack(), or setVisible(true) on your GUI.

Edit
You state:

I added the panel to the gui designer.. when the window pops up, i wanna now the real size of the jpanel, because it can change it.

If you want to know the size of a component held by a window “when the window pops up”, then add a WindowListener to the window and check the size of the component from the windowOpened(...) method.

Edit 2
Then you state:

after i have the real size, i add some subpanels, in relation to the size of this panel. so e.g. size/6 & the subpanel has now the size-height of size/6.

One Solution: Better not to set the sizes of anything but instead to use the right combination of layout managers and then let them set the proper sizes based on their rules.