//An instance of this class provides a method to spell an integer in words
//Public Interface
// Mutator : void setNumber(int number)
// Accessor: int getNumber()
// Method  : String spelling()
public class IntSpeller
{
   //Instance variable: any int value
   private int number;  
   
   //Accessor
   public int getNumber()
   {
      return this.number;
   }
   
   //Mutator  
   public void setNumber(int number)
   {
      this.number = number;
   }
   
   //Spelling Method
   // @return: the spelling (in words) of the instance variable
   public String spelling()
   {
      if (this.number == 0)
         return "Zero";
      
      //"Negative" prefix if the number < 0, work with absolute value
      int number = this.number;   
      String spelling = "";
      if (number < 0)
      {
         number = -number;
         spelling = "Negative ";
      }
      
      //Extend with the spelling of the BILLIONS part (if not 0)          
      int billions = number / 1000000000;
      if (billions != 0)
         spelling += threeDigitSpelling(billions) + " Billion ";
      
      //Extend with the spelling of the MILLIONS part (if not 0)   
      int millions = number % 1000000000 / 1000000;
      if (millions != 0)
         spelling += threeDigitSpelling(millions) + " Million ";
      
      //Extend with the spelling of the THOUSANDS part (if not 0)   
      int thousands = number % 1000000 / 1000;
      if (thousands != 0)
         spelling += threeDigitSpelling(thousands) + " Thousand ";

      //Extend with the spelling of the UNITS part (if not 0)
      int units = number % 1000;
      if (units != 0)
         spelling += threeDigitSpelling(units);   
         
      return spelling.trim();
   }
   
   //Helper Method
   // @param number: any positive 3-digit number
   // @return: the spelling (in words) of the parameter
   private static String threeDigitSpelling(int number)
   {
      if (number <= 0 || number > 999) //Validate the parameter
         throw new RuntimeException("Positive 3-digit number expected");
         
      //Split the number into its hundreds digit and 2-digit remainder
      int hundreds = number / 100;  //Hundreds digit
      int tensOnes = number % 100;  //2-digit remainder (tens & ones)
      
      String spelling = "";
      //Extend with the spelling of the HUNDREDS part (if not 0)
      if (hundreds > 0)
         spelling = onesWord(hundreds) + " Hundred ";
         
      //Extend with the spelling of the TENS & ONES part (if not 0)
      if (tensOnes != 0)
         spelling += twoDigitSpelling(tensOnes);
         
      return spelling.trim();
   }
   
   //Helper Method
   // @param number: any positive 2-digit number
   // @return: the spelling (in words) of the parameter
   private static String twoDigitSpelling(int number)
   {
      if (number <= 0 || number > 99) //Validate the parameter
         throw new RuntimeException("Positive 2-digit number expected");

      //Split the number into TENS and ONES digits
      int tens = number / 10;
      int ones = number % 10;
      
      String spelling = "";
      if (tens == 1)       //Spelling consists of a TEEN-word only
         spelling = teenWord(ones);
      else
      {
         if (tens > 1)     //Spelling begins with a TENS-word
            spelling = tensWord(tens) + " ";
         if (ones != 0)    //Spelling ends with a UNITS-word
            spelling = spelling + onesWord(ones);
      }
      return spelling.trim();
   }   
   
   //Helper Method
   // @param number: any single-digit integer
   // @return: the spelling of the parameter as a ONES/UNITS word
   private static String onesWord(int digit)
   {
      switch ( digit )
      {
         case 0 : return "Zero";
         case 1 : return "One";
         case 2 : return "Two";
         case 3 : return "Three";
         case 4 : return "Four";
         case 5 : return "Five";
         case 6 : return "Six";
         case 7 : return "Seven";
         case 8 : return "Eight";
         case 9 : return "Nine";
         default: throw new RuntimeException("Invalid digit " + digit);
      }
   }
       
   //Helper Method
   // @param number: any single-digit integer
   // @return: the spelling of the parameter as a TEEN word
   private static String teenWord(int digit)
   {
      switch ( digit )
      {
         case 0 : return "Ten";
         case 1 : return "Eleven";
         case 2 : return "Twelve";
         case 3 : return "Thirteen";
         case 4 : return "Fourteen";
         case 5 : return "Fifteen";
         case 6 : return "Sixteen";
         case 7 : return "Seventeen";
         case 8 : return "Eighteen";
         case 9 : return "Nineteen";
         default: throw new RuntimeException("Invalid digit " + digit);
      }
   }
   
   //Helper Method
   // @param number: any single-digit integer
   // @return: the spelling of the parameter as a TENS word
   private static String tensWord(int digit)
   {
      switch ( digit )
      {
         case 0 : return "Zero";
         case 1 : return "Ten";
         case 2 : return "Twenty";
         case 3 : return "Thirty";
         case 4 : return "Forty";
         case 5 : return "Fifty";
         case 6 : return "Sixty";
         case 7 : return "Seventy";
         case 8 : return "Eighty";
         case 9 : return "Ninety";
         default: throw new RuntimeException("Invalid digit " + digit);
      }
   }   
}