帮忙改几行程序,该如何解决

package ch7;import java.awt.Container;import java.awt.event.WindowAdapter;import java.awt.event.WindowEvent;import javax.swing.AbstractListModel;import javax.swing.BorderFactory;import javax.swing.JFrame;import javax.swing.JList;import javax.swing.JScrollPane;import javax.swing.ListModel;public class JList3{    public JList3()    {        JFrame f = new JFrame("JList");        Container contentPane = f.getContentPane();                ListModel mode = new DataModel();        JList list = new JList(mode);        list.setVisibleRowCount(5);        list.setBorder(BorderFactory.createTitledBorder("您最喜欢到哪个国家玩呢？"));                contentPane.add(new JScrollPane(list));        f.pack();        f.show();        f.addWindowListener(new WindowAdapter() {            public void windowClosing(WindowEvent e) {                    System.exit(0);            }        });    }        public static void main(String args[])    {        new JList3();    }}class DataModel extends AbstractListModel{    String[] s = {"美国","日本","大陆","英国","法国","意大利","澳洲","韩国"};    public Object getElementAt(int index)    {        return (index+1)+"."+s[index++];    }        public int getSize()    {        return s.length;    }}