我需要能够计算字母等级

Question

我已经能够计算输入的字母等级以及输入了多少等级。但是，我需要找到一种方法来计算每个字母等级的输入数量，请帮忙。

import java.util.*;


public class GradePercent {

    static final int THRESHOLD = 4;

    public static void main(String[] args) 
    {

        Scanner input = new Scanner(System.in);
        System.out.print("Enter the number of courses: ");
        int n = input.nextInt();
        System.out.print("Enter " + n + " scores: ");

        int[][] students = new int[3][n + THRESHOLD];

        for (int i = 0; i < n; i++){
            students[0][i] = input.nextInt();
        }

        int bestScore = getBestScore(students);
        setGradeRange(students, bestScore);

        for (int i = 0; i < students[0].length - THRESHOLD; i++) {
            char grade = getStudentGrade(students, i);
            System.out.println("Grade " + i + " score is " + students[0][i] + " and grade is " + grade);
        }
        System.out.println("Total grades: " + n );
    }

    public static char getStudentGrade(int[][] students, int index) 
    {

        int grade = students[0][index];
        for (int i = 0; i < 4; i++) 
        {
            if (grade >= students[1][i]) 
            {
                return (char) students[2][i];
            }
        }
        return 'F';
    }    

    public static void setGradeRange(int[][] students, int bestScore)
    {
            for (int i = 0; i < 4; i++) 
            {
                students[1][i] = bestScore - (10 * (i + 1));
                students[2][i] = ('A' + i);
            }
    }

    public static int getBestScore(int[][] students) {
        int bestScore = 100;
        return bestScore;
    }
    public static int[] countLetters(char[] chars) {
        int[] counts = new int[26];
        for (int i = 0; i < chars.length; i++)
            counts[chars[i] - 'A']++;
        return counts;
    }
}