Question

Once a JPanel has been instantiated and added to a visible JFrame, how do I add a new JComponent to it and update the display to show said new JComponent?

Original Question:

How to add JComponent to JPanel after JPanel has been added to a JFrame. I think I may have to extend JPanel and possibly override paintComponent().

Answer 1

JPanel.add() should work fine. If the frame is already visible, then call:

validate();
repaint();

Also, depending on the size and layout you may need to repack the frame with pack().

It is easier if you can post SSCCE with your question.