public boolean isWeekLetter(String letter)
    {
         boolean validLetter = false;

         if(letter.equals("SA"))
         {
             validLetter = true;
         }
         else if(letter.equals("SU"))
         {
             validLetter = true;
         }
         else if(letter.equals("TU"))
         {
             validLetter = true;
         }
         else if(letter.equals("TH"))
         {
             validLetter = true;
         }
         else if(letter.equals("MO"))
         {
             validLetter = true;
         }
         else if(letter.equals("WE"))
         {
             validLetter = true;
         }
         else if(letter.equals("FR"))
         {
             validLetter = true;
         }

         return validLetter;
     }