public class Numbers
{
   /**
      Counts the number of 7s in a given number
      @param num a number >= 0
      @return the number of digits in num that are 7
   */
   public static int countSevens(int num)
   {
      int count = 0;
      String str = Integer.toString(num);
      for(int i = 0; i < str.length(); i++)
      {
         if(str.charAt(i) == '7'){count++;}
      }
      return count;
   }
}