简单的成绩判定

import java.util.Scanner;
public class Stu{
public static void stuGrade(){
 Scanner input = new Scanner(System.in);
 String [] standard = {"E","G","M","F"};
 String [] grade = {"优秀","良好","中等","不合格"};
 messageshow("请输入学生状况:");
 String stu ;
 boolean judge = false;
 stu = input.next();
 for(int i = 0 ; i < standard.length ; i ++){
  if( stu.equals (standard [i])){
   System.out.println(grade [i]);
    judge = true;
    break;
   }
 }
  if(judge == true){
   messageshow("继续Y/N");
   String str = input.next();
   if(str.equals("Y"))
    stuGrade();
   else{
    messageshow("退出系统");
   }
  }  
  if(judge == false){
   messageshow("输入非法");
  }
}
public static void messageshow(String str){
 System.out.print(str);
}
 public static void main(String [] args){
  stuGrade();
 }
}