JAVA高手帮帮忙！！！JAVA的序列化问题！！！

定义一个可序列化的对象Student类，这个类实现了Serializable接口，类中的成员变量id，name，age，department都可以被序列化，方法不能序列化。通过对象输出流的writeObject（）方法将Student对象保存到文件data.ser中，然后通过对象输入流的readObject（）方法从文件data.ser中读出保存下来的Student对象，然后将Student对象的id和name输出到控制台。

import java.io.*;

class Student implements Serializable {
static private final long serialVersionUID = 123L;
int id;
String name;
int age;
String department;
public Student(int i, String n, int a, String d) {
id = i; name = n; age = a; department = d;
}
public String toString() {
return id + " " + name + " " + age + " " + department;
}
}

public class test {
public static void main(String[] args) throws FileNotFoundException, IOException, ClassNotFoundException {
ObjectOutputStream o =
new ObjectOutputStream(new FileOutputStream("D:\\sss.txt"));
o.writeObject(new Student(123, "C君", 18, "X部门"));
o.close();
ObjectInputStream i =
new ObjectInputStream(new FileInputStream("D:\\sss.txt"));
System.out.println(((Student)i.readObject()).toString());
i.close();
}
}