public class Letters
{
   /**
      Counts the frequencies of letters A-Za-z in a string
      @param str a string
      @return an array of 26 counts. The i-th count is the number of occurrences
      of 'A' + i or 'a' + i.
   */
   public int[] letterFrequencies(String str)
   {
      str.toLowerCase();
      int[] result = new int[26];
      char[] arrStr = str.toCharArray();
      for(char a : arrStr)
      {
         if(Character.isLetter(a)){result[Character.getNumericValue(a) - 10] += 1;}
      }
      return result;
   }
}