谁先来解决问题就给分最多，快点来哦

下面是我的程序，有个小小的错误 我找不到啊  请高手指点。import java.io.*;
public class ObjectSerialization 
{


public static void main(String[] args) throws IOException,ClassNotFoundException
 {

Student st = new Student(20010901,"黎明",20,"计算机系");
FileOutputStream fout = new FileOutputStream("data.txt");
ObjectOutputStream sout = new ObjectOutputStream(fout);

try
{
sout.writeObject(st);
sout.close();
}
catch(IOException e)
{

}

st = null;
FileInputStream fin = new FileInputStream("data.txt");
ObjectInputStream sin = new ObjectInputStream(fin);

try
{
st = (Student)sin.readObject();
sin.close();

}

catch(IOException e)
{
}

System.out.println("学生信息：");
System.out.println("学号："+st.id);
System.out.println("姓名："+st.name);
System.out.println("年龄："+st.age);
System.out.println("院系："+st.department);



}


class Student implements Serializable 
{
static int total;
transient boolean isEnrolled;

int id;
String name;
int age;
String department;
public Student()
{

}


public Student(int id,String name,int age,String department)
{
this.id = id;
this.name = name;
this.age = age;
this.department = department;
total++;
isEnrolled = true;
}

private void writeObject(ObjectOutputStream out) throws IOException
{
out.writeInt(id);
out.writeInt(age);
out.writeUTF(name);
out.writeUTF(department);
}

private void readObject(ObjectInputStream in) throws IOException
{
id = in.readInt();
age = in.readInt();
name = in.readUTF();
department = in.readUTF();
}
}
}