code: public static boolean isDouble(String _str, boolean _allowNegative) {
          return isDouble(_str, DecimalFormatSymbols.getInstance().getDecimalSeparator(), _allowNegative);
      }
docs: Checks if the given string is a valid double.
  The used separator is based on the used system locale
  @param _str string to validate
  @param _allowNegative set to true if negative double should be allowed
  @return true if given string is double, false otherwise