code: private JPanel getJContentPane() {
      if (jContentPane == null) {
        jContentPane = new JPanel();
        jContentPane.setLayout(new BorderLayout());
        jContentPane.add(getMainPanel(), BorderLayout.CENTER);
        jContentPane.add(getButtonPanel(), BorderLayout.SOUTH);
      }
      return jContentPane;
    }
docs: This method initializes jContentPane
  
  @return javax.swing.JPanel