code: protected JPanel buildButtonPanel() {
          buttonPanel = new JPanel();
  
          leftToRight = new JButton(">");
          allLeftToRight = new JButton(">>");
          rightToLeft = new JButton("<");
          allRightToLeft = new JButton("<<");
          Font smallerFont = leftToRight.getFont().deriveFont(9.0F);
          leftToRight.setFont(smallerFont);
          allLeftToRight.setFont(smallerFont);
          rightToLeft.setFont(smallerFont);
          allRightToLeft.setFont(smallerFont);
  
          Insets margin = new Insets(2, 4, 2, 4);
          leftToRight.setMargin(margin);
          allLeftToRight.setMargin(margin);
          rightToLeft.setMargin(margin);
          allRightToLeft.setMargin(margin);
  
          GridBagLayout gbl = new GridBagLayout();
          GridBagConstraints gbc = new GridBagConstraints();
  
          buttonPanel.setLayout(gbl);
  
          gbc.gridwidth = GridBagConstraints.REMAINDER;
          gbc.fill = GridBagConstraints.HORIZONTAL;
          gbl.setConstraints(leftToRight, gbc);
          gbl.setConstraints(allLeftToRight, gbc);
          gbl.setConstraints(rightToLeft, gbc);
          gbl.setConstraints(allRightToLeft, gbc);
  
          buttonPanel.add(leftToRight);
          buttonPanel.add(allLeftToRight);
          buttonPanel.add(rightToLeft);
          buttonPanel.add(allRightToLeft);
  
          leftToRight.addActionListener(new ActionListener() {
              public void actionPerformed(ActionEvent event) {
                  moveLeftToRight();
              }
          });
          allLeftToRight.addActionListener(new ActionListener() {
              public void actionPerformed(ActionEvent event) {
                  moveAllLeftToRight();
              }
          });
          rightToLeft.addActionListener(new ActionListener() {
              public void actionPerformed(ActionEvent event) {
                  moveRightToLeft();
              }
          });
          allRightToLeft.addActionListener(new ActionListener() {
              public void actionPerformed(ActionEvent event) {
                  moveAllRightToLeft();
              }
          });
  
          buttonPanel.setBorder(BorderFactory.createEmptyBorder(2, 2, 2, 2));
          // buttonPanel.setBackground( Color.lightGray );
          return buttonPanel;
      }
docs: Construct the control button panel.
  
  @return JPanel