SplitButton of dropdownbutton invisible when mouse clicking

click the SplitButton of dropdownbutton, when dropdownmenu willbe displayed. but this is not disabled when mouevent performed on the jpanel
how to disabled or hide the dropdownmenu when we click the dropdown button?
//the code is below

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.plaf.basic.BasicArrowButton;
public class SplitButton1 extends JButton
{
private JButton mainButton, dropDownButton;
private JMenu dropDownMenu;
public SplitButton1()
{
this(" ");
}
public SplitButton1(String text)
{
this(new JButton(text), SwingConstants.SOUTH);
}
public SplitButton1(String text, int orientation)
{
this(new JButton(text), orientation);
}
public SplitButton1(JButton mainButton, int orientation)
{
//super();
this.mainButton = mainButton;
this.dropDownButton = new BasicArrowButton(orientation);
//dropDownButton.addActionListener(this);
this.setBorderPainted(false);
this.dropDownButton.setBorderPainted(false);
this.mainButton.setBorderPainted(false);
this.setPreferredSize(new Dimension(75, 34));
this.setMaximumSize(new Dimension(75, 34));
this.setMinimumSize(new Dimension(200, 34));
this.setLayout(new BorderLayout());
this.setMargin(new Insets(-3, -3,-3,-3));
this.add(mainButton, BorderLayout.CENTER);
this.add(dropDownButton, BorderLayout.EAST);
}
public void setMenu(JMenu menu)
{
this.dropDownMenu = menu;
}
public JButton getMainButton()
{
return mainButton;
}
public JButton getDropDownButton()
{
return dropDownButton;
}
public JMenu getMenu()
{
return dropDownMenu;
}


public static void test()
{
JFrame frame = new JFrame("Simple Split Button Test");
frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
frame.getContentPane().setLayout(new BorderLayout());
JPanel p = new JPanel();
p.setLayout(new BorderLayout());
JToolBar toolBar = new JToolBar("tb");
JButton sbButton = new JButton(new ImageIcon("D:\\min.png"));
sbButton.setBackground(Color.BLACK);
sbButton.setContentAreaFilled(false);
SplitButton sb = new SplitButton(sbButton, SwingConstants.SOUTH);
//toolBar.add(new JButton("test button"));
toolBar.add(sb);
//p.add(new JLabel("SplitButton test"), BorderLayout.CENTER);
final JPopupMenu testMenu = new JPopupMenu("test menu");
testMenu.add("file");
testMenu.add("new");
sb.setMenu(testMenu);
testMenu.addSeparator();
frame.getContentPane().add(toolBar, BorderLayout.NORTH);
frame.getContentPane().add(p, BorderLayout.CENTER);
frame.setSize(200, 100);
frame.show();
frame.addMouseListener( new MouseAdapter()
{
public void mousePressed(MouseEvent evt)
{


}
} );


}
public static void main(String[] args)
{
test();
}
}