请各位帮下忙!

Question

    class Fontset extends JFrame implements ActionListener,ListSelectionListener
    {
   JFrame f=new JFrame("字体");
   JDialog dialog=new JDialog(f,"字体",true);
   String[] s1={"宋体","黑体","楷体","Arial","Courier","TimesRoman","Helvetica"};
   String[] s2={"常规","斜体","粗体"};
   String[] s3={"6","8","10","12","14","16","18","20"};
   JLabel lb1=new JLabel("字体(F):");
   JTextField tf1=new JTextField("黑体",5);
   JList lis1=new JList(s1);
   JLabel lb2=new JLabel("字形(Y):");
   JTextField tf2=new JTextField("常规",5);
   JList lis2=new JList(s2);
   JLabel lb3=new JLabel("大小(S):");
   JTextField tf3=new JTextField("12",3);
   JList lis3=new JList(s3);
   JButton bt1=new JButton("确定");
   JButton bt2=new JButton("取消");
   public Fontset()
   {
       Container diacp=dialog.getContentPane();
   diacp.setLayout(new FlowLayout());
   JPanel pal=new JPanel(new GridLayout(3,4,5,5));
   Container cp=getContentPane();
   Box bBox=Box.createHorizontalBox();
   cp.add(bBox);
   Box vBox1=Box.createVerticalBox();
   lb1.setAlignmentX(Component.LEFT_ALIGNMENT);
   vBox1.add(lb1);
   vBox1.add(Box.createVerticalStrut(2));
   tf1.setMaximumSize(new Dimension(150,5));
     vBox1.add(tf1);
   vBox1.add(Box.createVerticalStrut(2));
   lis1.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
   lis1.setVisibleRowCount(4);
           JScrollPane scroll1=new JScrollPane(lis1);
           scroll1.setBounds(10, 60,100 ,100);
           vBox1.add(scroll1);
   bBox.add(vBox1);
   bBox.add(Box.createHorizontalStrut(5));
   Box vBox2=Box.createVerticalBox();
   lb2.setAlignmentX(Component.RIGHT_ALIGNMENT);
   vBox2.add(lb2);
   vBox2.add(Box.createVerticalStrut(2));
   tf2.setMaximumSize(new Dimension(150,5));
   vBox2.add(tf2);
   vBox2.add(Box.createVerticalStrut(2));
   lis2.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
           lis2.setVisibleRowCount(4);
           lis2.setFixedCellHeight(20);
           JScrollPane scroll2=new JScrollPane(lis2);
   vBox2.add(scroll2);
   bBox.add(vBox2);
   bBox.add(Box.createHorizontalStrut(5));
   Box vBox3=Box.createVerticalBox();
   lb3.setAlignmentX(Component.RIGHT_ALIGNMENT);
   lb3.setAlignmentY(Component.TOP_ALIGNMENT);
   vBox3.add(lb3);
   vBox3.add(Box.createVerticalStrut(2));
   tf3.setMaximumSize(new Dimension(100,5));
   vBox3.add(tf3);
   vBox3.add(Box.createVerticalStrut(2));
   lis3.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
   lis3.setVisibleRowCount(4);
   lis3.setFixedCellHeight(20);
   JScrollPane scroll3=new JScrollPane(lis3);
   vBox3.add(scroll3);
   bBox.add(vBox3);
   bBox.add(Box.createHorizontalStrut(5));
   Box vBox4=Box.createVerticalBox();
   vBox4.add(bt1);
   vBox4.add(Box.createVerticalStrut(5));
   vBox4.add(bt2);
   bBox.add(vBox4);
   pal.add(bBox);
   diacp.add(pal);
   dialog.setSize(350,180);
   dialog.setVisible(true);
   dialog.setResizable(false);
   bt1.addActionListener(this);
   bt2.addActionListener(this);
   lis1.addListSelectionListener(this);
   lis2.addListSelectionListener(this);
   lis3.addListSelectionListener(this);
   }
   public void valueChanged(ListSelectionEvent e)
   {
int index1=lis1.getSelectedIndex();
                int index2=lis2.getSelectedIndex();
                int index3=lis3.getSelectedIndex();
                tf1.setText(s1[index1]);
                tf2.setText(s2[index2]);
                tf3.setText(s3[index3]);
   }
           public void actionPerformed(ActionEvent exc)
   {
    String cmd=exc.getActionCommand();
    if(cmd.equals("确定"))
    {
   
    }
    if(cmd.equals("取消"))
    {
    f.dispose();
    }
   }
    }
在上面的程序中为什么在JTextField(tf1)中无法显示JList中的字符
我是想设置字体对话框