Adding a menu bar to a JSplitPane

Main.java:

 
import javax.swing.plaf.basic.*;
import java.awt.event.*;
import javax.swing.*;
import java.beans.*;
import java.awt.*;
 
public class Main extends JFrame
{
   JSplitPane splitPane;
  
   public Main() {
      addWindowListener(new WindowAdapter() {
         public void windowClosing(WindowEvent we) {
            System.exit(0);
         }
      });
 
      splitPane = new JSplitPane(JSplitPane.VERTICAL_SPLIT, 
                                 new JPanel(), new JPanel());
      splitPane.setDividerSize(20);
  
      splitPane.setUI(new MenuDividerUI(getMainMenuBar()));
 
      getContentPane().add(splitPane);
 
      addComponentListener(new ComponentAdapter() {
         public void componentShown(ComponentEvent event) {
            splitPane.setDividerLocation(0.5);  
                
            removeComponentListener(this);
         }
      });
   }
 
   public JMenuBar getMainMenuBar() {
      JMenuBar mainBar = new JMenuBar();
      JMenu menu = new JMenu("JSplitPane");
      JMenuItem item1 = new JMenuItem("HORIZONTAL_SPLIT");
      JMenuItem item2 = new JMenuItem("VERTICAL_SPLIT");
      menu.add(item1);
      menu.add(item2);
      mainBar.add(menu);
  
      item1.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent ae) {
            splitPane.setOrientation(JSplitPane.HORIZONTAL_SPLIT);
         }
      });
 
      item2.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent ae) {
            splitPane.setOrientation(JSplitPane.VERTICAL_SPLIT);
         }
      });
 
      return mainBar;
   }
 
   public static void main(String []args) {
      Main main = new Main();
      main.setSize(300, 300);
      main.setVisible(true);
   }
}
 
class MenuDividerUI extends BasicSplitPaneUI
{
   protected JMenuBar menuBar;
 
   public MenuDividerUI(JMenuBar menuBar) {
      this.menuBar = menuBar;
   }
 
   public BasicSplitPaneDivider createDefaultDivider() {
      BasicSplitPaneDivider divider = new BasicSplitPaneDivider(this) {
         public int getDividerSize() { return menuBar.getPreferredSize().height; }
      };
      divider.setLayout(new BorderLayout());
      divider.add(BorderLayout.NORTH, menuBar);
 
      return divider;
   }
}