public class PhoneNumbers
{
   /**
      Cleans a phone number.
      @param phoneNumber a phone number that should contain ten digits and possibly other characters
      @return the phone number in the form (###) ###-#### or the string "Error" if phoneNumber
      does not have ten digits
   */
   public String cleanNumber(String phoneNumber)
   {
      // your work here
      String number = "";
      for (int i = 0; i < phoneNumber.length(); i++)
      {
         char ch = phoneNumber.charAt(i);
         if (Character.isDigit(ch))
         {
            number += ch;
         }
      }
      if(number.length() != 10){return "Error";}
      return String.format("(%c%c%c) %c%c%c-%c%c%c%c"
      , number.charAt(0), number.charAt(1), number.charAt(2)
      , number.charAt(3), number.charAt(4), number.charAt(5)
      , number.charAt(6), number.charAt(7), number.charAt(8)
      , number.charAt(9));
   }
}