I wrote some code overwriting JPanel's paintComponent() method and put it in a convenience JFrame.
When I run it the Rectangle drawn in paintComponent() is sometimes shown and sometimes it isn't. If it isn't I have to force a repaint by changing JFrame's size and then it is shown ... bizarre! Any Ideas, anybody?
Thanks in advance for any hint on how to solve this problem.
When you add a component to a container after it (s top-level container) has been realized you have to let it know so it can do a new layout. We usually do this with the Container method validate or the JComponent method revalidate. Sometimes you may need to follow this (validation) with a call to repaint, but not always.