Hey this might help you. I already had this one.

import java.util.*;
import java.text.*;

public class GPACalculator {

    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.print("How many subjects do you have?: ");
        int classes = input.nextInt();
        String grades = "";
        double total = 0;
        double dec;

        for (int j = 0; j < classes; j++) {

            Scanner inputs = new Scanner(System.in);
            System.out.print("What is your Grade in subject "+(j+1)+" ?: ");
            grades = inputs.nextLine();

            if (grades.equals("A")){
                dec = 4;
                total += dec;

            } else if (grades.equals("B")){
                dec = 3;
                total += dec;

            } else if (grades.equals("C")){
                dec = 2;
                total += dec;

            } else if (grades.equals("D")){
                dec = 1;
                total += dec;

            } else if (grades.equals("F")){
                dec = 0;
                total += dec;
            }
        }

        double GPA = total / classes;
        System.out.println("Your GPA is "+GPA);

        DecimalFormat formatter = new DecimalFormat("0.##");
        System.out.println("If required in formatted form :"+formatter.format(GPA));
    }
}

You can change as per your grade value.