Main.java

package com.company;

import java.io.*;
import java.util.ArrayList;
import java.util.Random;
import java.util.Scanner;

public class Main {

    public static String getRandomAnswers(){
        Random random = new Random();
        StringBuilder answers = new StringBuilder();
        do{
            int rand = random.nextInt(100);
            if (rand % 2 == 0) {
                answers.append("F");
            }
            else if (rand % 4 == 3) {
                answers.append(" ");
            }
            else {
                answers.append("T");
            }
        }while(answers.length() != 20);
        return answers.toString();
    }

    public static void main(String []args) throws IOException {
        int stdCounter = 1;
        StringBuilder longString = new StringBuilder();
        longString.append("TFFTFFTTTTFFTFTFTFTT\n");
        do {
            longString.append(String.format("STUDENT00%s %s\n", stdCounter, getRandomAnswers()));
            stdCounter++;
        }while (stdCounter <= 15);
        FileWriter wr = new FileWriter("students.txt");
        wr.write(longString.toString());
        wr.close();

        File studentAnswers = new File("students.txt");
        Scanner answerScanner = new Scanner(studentAnswers);
        char[] correctAnswer = {};
        while (answerScanner.hasNextLine()) {
            if (correctAnswer.length == 0) {
                correctAnswer = answerScanner.nextLine().toCharArray();
            }
            else {
                String[] data = answerScanner.nextLine().split(" ", 2);
                String studentId = data[0];
                String answers = data[1];
                double points = 0;
                char[] x = answers.toCharArray();
                for (int i = 0; i<x.length; i++) {
                    char ans = x[i];
                    if (ans == ' ') {
                        points += 0f;
                    }
                    else if (ans == correctAnswer[i]) {
                        points += 2f;
                    }
                    else if (ans != correctAnswer[i]){
                        points -= 1f;
                    }
                }
                double grade = (points / 40.0f) * 50.0f + 50.0f;
                char mark = 'F';
                if (grade >= 90 && grade <= 100)
                    mark = 'A';
                else if (grade >= 80 && grade <= 89.99)
                    mark = 'B';
                else if (grade >= 70 && grade <= 79.99)
                    mark = 'C';
                else if (grade >= 60 && grade <= 69.99)
                    mark = 'D';

                System.out.println(String.format("%s %s (%s %s", studentId, answers, mark, grade) + "%)");
            }

        }
    }
}