Java Algorithms Convert number to English words example 4

public class Main {
   public static final String[] units = { "", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine",
         "ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen" };

   public static final String[] tens = { "", // 0
         "", // 1
         "twenty", // 2
         "thirty", // 3
         "forty", // 4
         "fifty", // 5
         "sixty", // 6
         "seventy", // 7
         "eighty", // 8
         "ninety" // 9
   };//from w  w  w .  j  av a  2s .  c  o m

   public static String convert(final int n) {
      if (n < 0) {
         return "minus " + convert(-n);
      }

      if (n < 20) {
         return units[n];
      }

      if (n < 100) {
         return tens[n / 10] + ((n % 10 != 0) ? " " : "") + units[n % 10];
      }

      if (n < 1000) {
         return units[n / 100] + " hundred" + ((n % 100 != 0) ? " " : "") + convert(n % 100);
      }

      if (n < 1000000) {
         return convert(n / 1000) + " thousand" + ((n % 1000 != 0) ? " " : "") + convert(n % 1000);
      }

      if (n < 1000000000) {
         return convert(n / 1000000) + " million" + ((n % 1000000 != 0) ? " " : "") + convert(n % 1000000);
      }

      return convert(n / 1000000000) + " billion" + ((n % 1000000000 != 0) ? " " : "") + convert(n % 1000000000);
   }

   public static void main(final String[] args) {
      int n = 1000;
      System.out.printf("%10d =  '%s'%n", n, convert(n));

      n = 11000;
      System.out.printf("%10d =  '%s'%n", n, convert(n));

      n = 999999999;
      System.out.printf("%10d =  '%s'%n", n, convert(n));

      n = Integer.MAX_VALUE;

      System.out.printf("%10d =  '%s'%n", n, convert(n));
   }
}