вррпа

import javax.swing.*;

public class ReportCard {

    public char convertGrades(int testResult) {
        char grade;
        if (testResult >= 90) {
            grade = 'A';
        } else if (testResult >= 80 && testResult < 90) {
            grade = 'B';
        } else if (testResult >= 70 && testResult < 80) {
            grade = 'C';
        } else {
            grade = 'D';
        }
        return grade;
    }

    public static void main(int testResult) {
        ReportCard rc = new ReportCard();
        char grade = JOptionPane.showInputDialog(rc.convertGrades, "Введите");
        switch (grade) {
        case 'A':
            JOptionPane.showMessageDialog(null, "Отлично!");
            break;
        case 'B':
            JOptionPane.showMessageDialog(null, "Хорошо!");
            break;
        case 'C':
            JOptionPane.showMessageDialog(null, "Удовлетворительно!");
            break;
        case 'd':
            JOptionPane.showMessageDialog(null, "Неудовлетворительно!");
            break;
        }
    }
}