帮忙修改这个程序java

public class StudentScoreTest
{
public static void main(String args[])throws IOException
{
String k,n,s;
int a;

BufferedReader in=new BufferedReader(new InputStreamReader(System.in));
System.out.println("请输入最大学生人数:");
s= in.readLine();
a=Integer.parseInt(s);
StudentScore sg=new StudentScore(a);
Student x=new Student("李四","002",86,92,97,3.7,"345");
Student y=new Student("张三","001",90,95,96,4.0,"123");

sg.append(x);
sg.append(y);

while(true)
{
System.out.println("**请选择您的身份**");
System.out.println(" 0.退出系统");
System.out.println(" 1.用户");
System.out.println(" 2.管理员");
System.out.println("***************");