code: protected boolean containsSubstring(char[] substring, int startIndex) {
  
      if (substring.length < (this.string.length - startIndex)) {
        for (int i = 0; i < substring.length; i++) {
          if (substring[i] != this.string[startIndex + i]) {
            return false;
          }
        }
        return true;
      }
      return false;
    }
docs: This method tests if the string to tokenize contains the given {@code substring} starting at the given
  {@code index}.
  
  @param substring is the substring to check for.
  @param startIndex is the start index in the string to tokenize.
  @return {@code true} if the given {@code substring} was found at {@code index}.