code: public static boolean isLetterNumber(char c) {
  		return (c >= 'a' && c <= 'z') || (c >= '0' && c <= '9') || (c >= 'A' && c <= 'Z') || c == '_' || c == '.'
  				|| c == '@' || c == '#' || c == '$' || c == '+' || c == '-';
  	}
docs: ==================String Utils below======================