求助关于java滚动条

import java.awt.Container;
import java.awt.Dimension;
import java.awt.Toolkit;

import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;


public class Scroll extends JFrame{
    private Container container;    
    public Scroll(){
        super("滚动条");
        
        container = getContentPane();
        container.add(new JScrollPane(new JTextArea(10,50)));
        
        pack();
        
        Dimension frameSize = getSize();
        Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
        setLocation((screenSize.width - frameSize.width)/2,(screenSize.height - frameSize.height)/2);
        setVisible(true);
    }
    public static void main(String[] args) {
        new Scroll();
    }
}