مشكلة مع Scrollpane

import java.awt.event.*;
import javax.swing.*;
import java.awt.*;
public class scrolltest extends JFrame{
JDesktopPane desk=new JDesktopPane();
JMenuBar bar=new JMenuBar();
JMenu file=new JMenu("file");
JMenuItem enter=new JMenuItem("item",'ا');

public scrolltest() {
super("desk");
file.add(enter);
bar.add(file);
setJMenuBar(bar);
this.add(desk);
enter.addActionListener(
new ActionListener() {
public void actionPerformed( ActionEvent event )
{
panel p=new panel();
JInternalFrame frame=new JInternalFrame( "title", true, true, true, true);




JScrollPane sp=new JScrollPane(p);
getContentPane().add(sp);


add(sp);
frame.setPreferredSize( new Dimension( 150, 120) );
desk.add(frame);
frame.setVisible( true );
}}); }
public static void main (String args[]){
scrolltest frame =new scrolltest();
frame.setTitle("title");
frame.setLocationRelativeTo(null);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(200,200);

frame.setVisible(true);
}}

package test;

import javax.swing.*;
import java.awt.*;
public class panel extends JPanel{

JButton b1=new JButton("b");
JButton b2=new JButton("b");
JButton b3=new JButton("b");
JTextField t1=new JTextField();
JTextField t2=new JTextField();
JTextField t3=new JTextField();

public panel() {
setLayout(new GridLayout( 3,2));
add(b1);
add(b2);
add(b3);
add(t1);
add(t2);
add(t3);
}


}

package test;