/*  Revise Example 4.3 to use an isValid method
 *  and to input the score in the main method.
 *  It is a design alternative.
 */

import javax.swing.*;

public class Score {
  int score;

  public Score(int s) {
    score = s;
  }
  public boolean isValid() {
    if (score >= 0 && score <= 100)
      return true;
    else
      return false;
  }
  public String letterGrade() {
      String grade = "";
      if (score < 50)
        grade =  "F";
      else if (score >= 50 && score < 60)
        grade =  "D";
      else if (score >= 60 && score < 80)
        grade =  "C";
      else if (score >=80 && score < 90)
        grade =  "B";
      else if (score >= 90 && score <= 100)
        grade =  "A";
      return grade;
  }
  public static void main(String [] args) {
    String input = JOptionPane.showInputDialog
                         ("Enter a score (0-100)");
    int temp = Integer.parseInt(input);
    Score s = new Score(temp);
    String message = "Score is not valid";
    if (s.isValid())
      message = "Grade: " + s.letterGrade();
    JOptionPane.showMessageDialog(null, message);
    System.exit(0);
  }
}