code: public static int occurrencesOf(String string, String singleCharacter)
      {
          if (singleCharacter.length() != 1)
          {
              throw new IllegalArgumentException("Argument should be a single character: " + singleCharacter);
          }
          return StringIterate.occurrencesOfChar(string, singleCharacter.charAt(0));
      }
docs: Count the number of occurrences of the specified {@code string}.