Library Overdue

/*** Overdue Library Books **************************
Sheila works in the school library.  She needs a quick way
to calcuate a fine for overdue books, based on this table:
   0.25 per day, up to 6 days.
   1.50 for 7-13 days
   3.00 for 14-20 days
   etc, 1.50 per week for each week
The logic is not difficult, but it's much simpler if she
can type in the original due date and the current date,
and the computer tells the appropriate fine.
*****************************************************/
public class OverdueBooks
{
  public OverdueBooks()
  {
    String today = input("Today's date (dd.mm)");
    String another = "";
    while(another.equals(""))
    {
      String dueDate = input("Due date (dd.mm)");
      int days = daysLate(today, dueDate);
      System.out.println("Today = " + today);
      System.out.println("Due = " + dueDate);
      System.out.println("Days overdue = " + days);

      if(days<=0)
      { System.out.println("No fine"); }
      else if(days<=6)
      { System.out.println("Fine = " + (days*0.25)); }
      else if(days<=13)
      { System.out.println("Fine = " + 1.50); }
      else if(days<=20)
      { System.out.println("Fine = " + 3.00); }
      else if(days<=27)
      { System.out.println("Fine = " + 4.50); }
      else
      { System.out.println("Over 4 weeks late - talk to librarian"); }
      another = input("Press [Enter] for another book");
    }
  }

  int daysLate(String today,String dueDate)
  {
    int td = Integer.parseInt(today.substring(0,2));    // today's day
    int tm = Integer.parseInt(today.substring(3,5));    // today's month

    int dd = Integer.parseInt(dueDate.substring(0,2));  // dueDate's day
    int dm = Integer.parseInt(dueDate.substring(3,5));  // dueDate's month

    if(tm == dm)
    {
      if(dd >= td)
      {  return -1; }                     // not overdue
      else
      {  return td-dd; }                  // days overdue
    }
    else if (dm > tm)
    {  return -1; }                        // not overdue
    else
    {                                      // tm > dm, due last month
      return (tm-dm)*30 + (td-dd);        // count 30 days per month
    }
  }

  public static void main(String[] args)
  {  new OverdueBooks();  }

  public String input(String prompt)
  { return javax.swing.JOptionPane.showInputDialog(null,prompt); }
}