public void saveStudentsToFile(Student[] students) {
    FileWriter fw = new FileWriter("plik, ABSOLUTE PATH SMIECIU");
    BufferedWriter bw = new BufferedWriter(fw);
    for (int i = 0; i < students.length; i++) {
        Student student = students[i];
        String output = String.format("%s|%s|%s|%s", student.getName(), student.getSurname(),
                                                     student.getAge(), student.getAverage());
        Marks[] marks = student.getMarks();
        for (int j = 0; j < marks.length; j++) {
            Mark mark = marks[j];
            output += String.format("|%s:%s", mark.getSubject().getName(), mark.getMark());
        }
        bw.write(output)
        bw.newLine()
    }
    bw.close()
}

public void saveTeacherTofile(Teacher[] teachers) {
    FileWriter fw = new FileWriter("plik, ABSOLUTE PATH SMIECIU");
    BufferedWriter bw = new BufferedWriter(fw);
    for (int i = 0; i < teachers.length; i++) {
        Teacher teacher = teacher[i];
        String output = String.format("%s|%s|%s|%s|%s", teacher.getName(), teacher.getSurname(),
                                                        teacher.getFirstSubject().getName(), teacher.getSecondSubject().getName());
        bw.write(output)
        bw.newLine()
    }
    bw.close()
}