Student Improved

import java.io.*;
class Student
{
    int sub1, sub2, sub3;
    double avg;
    String name;
    // NEW:
    Student()
    {
        this("", 0, 0, 0);
    }
    Student(String name, int a, int b, int c)
    {
        this.name = name;
        sub1=a;
        sub2=b;
        sub3=c;
        avg=0.0;
    }
    char calc()
    {
        avg=(sub1+sub2+sub3)/3;
        if(avg>=90)
        return 'O';
        else if(avg>=80 && avg<90)
        return 'A';
        else if(avg>=70 && avg<80)
        return 'B';
        else if(avg>=50 && avg<70)
        return 'C';
        else
        return 'F';
    }
    void input()throws IOException
    {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        System.out.println("Enter name");
        name=br.readLine();
        System.out.println("Enter marks in three subjects");
        boolean correct_marks_entered = true;
        // NEW:
        do{
            try{
                sub1 = Integer.parseInt(br.readLine());
                sub2= Integer.parseInt(br.readLine());
                sub3= Integer.parseInt(br.readLine());
                if(sub1<0 || sub1>100)
                {
                    correct_marks_entered = false;
                    throw new T(1, sub1);
                }
                else if(sub2<0 || sub2>100)
                {
                    correct_marks_entered = false;
                    throw new T(2, sub2);
                }
                else if(sub3<0 || sub3>100)
                {
                    correct_marks_entered = false;
                    throw new T(3, sub3);
                }
                correct_marks_entered = true;
            }
            catch(T e)
            {
                System.out.println(e);
            }
        }while(!correct_marks_entered);
    }
    void display()
    {
        char c= calc();
        System.out.println("Name: "+name+"\nAverage: "+avg+"\nGrade :"+c);
    }
    public static void main(String args[])throws Exception
    {
        // OLD:
        //Student obj = new Student("Ann", 55, 66, 77);
        Student obj = new Student();
        obj.input();
        obj.display();
    }
}

class T extends Exception{
    int subject_no;
    int marks;
    T(int subject_no, int marks){
        this.subject_no = subject_no;
        this.marks = marks;
    }
    public String toString(){
        return "Exception caught with " + subject_no + " subject marks\n" +
                marks + " is an invalid marks. Range is 0-100";
    }
}