帮忙看下这个程序读取的问题 怎么不能连续读取数据

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.io.*;
public class Form{
public static void main(String[] args) throws IOException{
JFrame.setDefaultLookAndFeelDecorated(true);
JFrame f=new JFrame("学生登记表");
f.setSize(400,150);
f.setLocation(300,200);
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Container contentPane=f.getContentPane();
contentPane.setLayout(new GridLayout(2,1));
JPanel panel1=new JPanel();
JPanel panel2=new JPanel();
panel1.setLayout(new GridLayout(3,2));
panel2.setLayout( new FlowLayout());
JLabel label1=new JLabel("姓名",SwingConstants.CENTER);
JLabel label2=new JLabel("性别",SwingConstants.CENTER);
JLabel label3=new JLabel("年龄",SwingConstants.CENTER);
final JTextField textfield1=new JTextField("",20);
final JTextField textfield2=new JTextField("",20);
final JTextField textfield3=new JTextField("",20);
JButton button1=new JButton("确定");
JButton button2=new JButton("读取");
JButton button3=new JButton("退出");

panel1.add(label1);
panel1.add(textfield1);
panel1.add(label2);
panel1.add(textfield2);
panel1.add(label3);
panel1.add(textfield3);
panel2.add(button1);
panel2.add(button2);
panel2.add(button3);
contentPane.add(panel1);
contentPane.add(panel2);
final JDialog d=new JDialog();
button1.addActionListener(new ActionListener(){       //点击确定的事件
public void actionPerformed(ActionEvent event)
{
String fileName="D:\\student.txt";
try{
BufferedWriter write=new BufferedWriter(new FileWriter(fileName,true));
String name=textfield1.getText();
write.write(name);
write.newLine();
String sex=textfield2.getText();
write.write(sex);
write.newLine();
String age=textfield3.getText();
write.write(age);
write.newLine();
write.close();}
catch(Exception iox)
{
iox.printStackTrace();
}
if(textfield1.getText()==""||textfield2.getText()==""
||textfield3.getText()=="")
{
JOptionPane.showMessageDialog(d, "注册信息不能为空","请重新输入",JOptionPane.WARNING_MESSAGE);
textfield1.setText("");
//textfield2.setText("");
textfield3.setText("");
}
textfield1.setText("");
textfield2.setText("");
textfield3.setText("");
}
});
button2.addActionListener(new ActionListener(){   //单击读取按钮
public void actionPerformed(ActionEvent event){
String fileName="D:\\student.txt";

try
{
BufferedReader in=new BufferedReader(new FileReader("D:\\student.txt"));
textfield1.setText(in.readLine());
textfield2.setText(in.readLine());
textfield3.setText(in.readLine());

in.close();
}
catch(IOException iox)
{
System.out.print("读文件有问题"+fileName);
}
}
});
button3.addActionListener(new ActionListener(){   //退出系统
public void actionPerformed(ActionEvent event){
System.exit(0);
}
});

f.setVisible(true);
}
}