Hello

I have a Swing application and I'm trying to do the following:

I have a main JFrame in which JPanels are loaded based on events. Now,
I have a particular JPanel which in turn has 2 child JPanels. However,
both these panels are not created at the same time. I create one of the
2 initially and if the user clicks a button on the first JPanel, the
second is created. I am using the GridBagLayout.

My problem is this: When I create the first of 2 JPanels, it shows up
fine. When I click the button to create the second JPanel, the first
one changes its size and everything and appears totally weird. How can
I retain my first created JPanel's appearance and have my second JPanel
appear right too?

Following is code:

class MultiplePanels
{
   JPanel pan;
   JPanel mainPanel;
   JPanel secPanel;

   public void createPanel()
   {
       // Parent JPanel which is a component of the JFrame
       pan = new JPanel();
       pan.setLayout(new GridBagLayout());
       pan.setPreferredSize(new Dimension(780, 500));

       // 1st child JPanel
       mainPanel = new JPanel();
       mainPanel.setPreferredSize(780, 250);
       mainPanel.setLayout(new GridBagLayout());

       // Adding button to JPanel
       JButton b = new JButton("Create new JPanel");
       b.addActionListener(this);
       // ........... adding other components to mainPanel

       GridBagConstraints c = new GridBagConstraints();
       c.gridy = 0;
       c.anchor = GridBagConstraints.NORTH;
       c.weighty = 1;
       pan.add(mainPanel, c);
   }

   public void actionPerformed(ActionEvent e)
   {
       // 2nd child JPanel
       secPanel = new JPanel();
       secPanel.setPreferredSize(780, pan.getHeight() -
mainPanel.getHeight());
       GridBagConstraints c = new GridBagConstraints();
       c.gridy = 1;
       c.anchor = GridBagConstraints.SOUTH;
       
       pan.add(secPanel, c);
   }
}