求助，照着老师敲的代码，只是有些小改动而已，出现不能读取问题。

import java.awt.BorderLayout;
import java.awt.Button;
import java.awt.CardLayout;
import java.awt.Color;
import java.awt.Font;
import java.awt.Label;
import java.awt.Menu;
import java.awt.MenuBar;
import java.awt.MenuItem;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.io.File;
import java.io.RandomAccessFile;
import javax.swing.Box;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.SwingConstants;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;
public class shang extends JFrame implements ActionListener,DocumentListener
{
    File file = null;   
    MenuBar menubar;
    Menu menu;
    MenuItem menuitem1,menuitem2,menuitem3;
    JTextArea textarea;
    JPanel panel1,panel2,panel3;
    Button button1,button2;
    Box basebox,box1,box2;
    JTextField textfield1,textfield2,textfield3,textfield4,textfield5;
    CardLayout card;
    Boolean t = false;
    Boolean k = false;
//    JLabel l = null;
   
    public shang()
    {
        menubar = new MenuBar();
        file = new File("记录.txt");
        this.setMenuBar(menubar);
        menu = new Menu("菜单选项");
        menuitem1 = new MenuItem("录入");
        menuitem2 = new MenuItem("显示");
        menuitem3 = new MenuItem("主页面");
      
        card = new CardLayout();
        panel1 = new JPanel();
        panel3 = new JPanel();
        panel2 = new JPanel();
        JPanel jpanel = new JPanel();
    //    l = new JLabel();
    //    l = new JLabel("信息查询",JLabel.CENTER);
    //    l.setIcon(new ImageIcon("welcome.jpg"));
    //    l.setFont(new Font("宋体",Font.PLAIN,18));
    //    l.setHorizontalTextPosition(SwingConstants.CENTER);
    //    l.setForeground(Color.red);
        panel1.setLayout(card);
        panel3.setBackground(Color.darkGray);
        panel2.setLayout(new BorderLayout());
        textarea = new JTextArea(350,350);            //文本域
        JTextArea text1 = new JTextArea(2,20);
        JScrollPane text = new JScrollPane(text1);            //滚动条
        menubar.add(menu);
        menu.add(menuitem3);
        menu.add(menuitem1);
        menu.add(menuitem2);
      
        button1 = new Button("录入");
        button2 = new Button("显示");
   
        textfield1 = new JTextField(15);
        textfield2 = new JTextField(15);
        textfield3 = new JTextField(15);
        textfield4 = new JTextField(15);
        textfield5 = new JTextField(15);
        textfield1.setFont(new Font("宋体", Font.PLAIN, 14));
        textfield2.setFont(new Font("宋体", Font.PLAIN, 14));
        textfield3.setFont(new Font("宋体", Font.PLAIN, 14));
        textfield4.setFont(new Font("宋体", Font.PLAIN, 14));
        textfield5.setFont(new Font("宋体", Font.PLAIN, 14));
        textfield3.getDocument().addDocumentListener(this);
        textfield4.getDocument().addDocumentListener(this);
   
   
        box1 = Box.createVerticalBox();
        box1.add(new Label("货物编号"));
        box1.add(Box.createVerticalStrut(11));
        box1.add(new Label("货物名称"));
        box1.add(Box.createVerticalStrut(11));
        box1.add(new Label("单价"));
        box1.add(Box.createVerticalStrut(11));
        box1.add(new Label("数量"));
        box1.add(Box.createVerticalStrut(11));
        box1.add(new Label("金额"));
        box1.add(Box.createVerticalStrut(11));
        box2 = Box.createVerticalBox();
        box2.add(textfield1);
        box2.add(Box.createVerticalStrut(8));
        box2.add(textfield2);
        box2.add(Box.createVerticalStrut(8));
        box2.add(textfield3);
        box2.add(Box.createVerticalStrut(8));
        box2.add(textfield4);
        box2.add(Box.createVerticalStrut(8));
        box2.add(textfield5);
        box2.add(Box.createVerticalStrut(8));
        basebox = Box.createHorizontalBox();
        basebox.add(box1);
        basebox.add(Box.createHorizontalStrut(15));
        basebox.add(box2);
        panel3.add(basebox);
        jpanel.add(button1);
        jpanel.add(button2);
        panel2.add(jpanel,BorderLayout.SOUTH);
        panel2.add(panel3,BorderLayout.CENTER);
//        panel1.add(l);
        panel1.add(panel2);
        panel1.add(text);
//        panel1.add("1",l);
        panel1.add("2",panel2);
        panel1.add("3",text);
      
        this.add(panel1,BorderLayout.CENTER);
        setSize(400,400);
        setLocation(300,85);
        setVisible(true);
   
        menuitem1.addActionListener(this);
        menuitem2.addActionListener(this);
        menuitem3.addActionListener(this);
        button1.addActionListener(this);
        button2.addActionListener(this);
      
   
        addWindowListener(new WindowAdapter()
        {
             public void windowClosing( WindowEvent e )
             {
                 System.exit( 0 );
             }
        });
    }
    public void actionPerformed(ActionEvent e)
    {
//        if(e.getSource() == menuitem3)
//            cl.show(panel1,"1");
        if(e.getSource() ==menuitem1 || e.getSource() == button1)
        {
            card.show(panel1,"2");
            t = true;
        //    k = true;
        }
        if(t)                    //写入数据
        {
            try{
                RandomAccessFile out = new RandomAccessFile(file, "rw");
                if(file.exists())
                {
                    long length = file.length();
                    out.seek(length);
                }
                out.writeUTF("货物编号"+textfield1.getText());
                out.writeUTF("货物名称"+textfield2.getText());
                out.writeUTF("单价"+textfield3.getText());
                out.writeUTF("数量"+textfield4.getText());
                out.writeUTF("金额"+textfield5.getText());
                out.close();
            }catch(Exception a)
            {}
    /*        f1.setText("");
            f2.setText("");
            f3.setText("");
            f4.setText("");
            f5.setText("");    */
        }
        if(e.getSource() ==menuitem2 || e.getSource() == button2)
        {
            if(textfield1.getText().isEmpty())
                JOptionPane.showMessageDialog(null, "编号不能为空");                           
                else if(textfield2.getText().isEmpty())
                    JOptionPane.showMessageDialog(null, "名称不能为空");
                    else if(textfield3.getText().isEmpty())
                        JOptionPane.showMessageDialog(null, "单价不能为空");
                        else if(textfield4.getText().isEmpty())
                            JOptionPane.showMessageDialog(null, "数量不能为空");
                            else if(textfield5.getText().isEmpty())
                                JOptionPane.showMessageDialog(null, "金额不能为空");
            else
            {
                card.show(panel1,"3");        //转至文本域
                t = false;
                textarea.setText(null);
                int count = 1;
                try                    //读取数据
                {
                    String file = null;
                    RandomAccessFile in = new RandomAccessFile(file,"r");
                    String 货物编号 = null;
                    while((货物编号 = in.readUTF())!=null)
                    {
                        textarea.append("\n"+count+" "+货物编号);
                        textarea.append(in.readUTF());
                        textarea.append(in.readUTF());
                        textarea.append(in.readUTF());
                        textarea.append(in.readUTF());
                        textarea.append("\n-----------------------------");
                        count ++ ;
                    }
                    in.close();
                }catch(Exception a)
                {}
            }
        }
    }

    public static void main(String[] shang)
    {
        new shang();
    }
    public void changedUpdate(DocumentEvent e)
    {
        doChange();
    }
    public void insertUpdate(DocumentEvent e)
    {
        doChange();
    }
    public void removeUpdate(DocumentEvent e)
    {
        doChange();
    }
    private void doChange()
    {
        try
        {
            int n1 = Integer.parseInt(textfield3.getText());
            int n2 = Integer.parseInt(textfield4.getText());
            textfield5.setText(String.valueOf(n1*n2));
        } catch (Exception ee)
        {}
    }
}