javaParseDouble function

double? javaParseDouble(String input)

Java Double.parseDouble: trims characters <= ' ', accepts an optional sign, NaN, Infinity, decimal and exponent notation, a trailing f/F/d/D, and hexadecimal floating point. Returns null where Java throws NumberFormatException.

Implementation

double? javaParseDouble(String input) {
  final s = javaTrim(input);
  final decimal = _javaDecimal.firstMatch(s);
  if (decimal != null) {
    final negative = decimal.group(1) == '-';
    final value = switch (decimal.group(2)!) {
      'NaN' => double.nan,
      'Infinity' => double.infinity,
      // Dart rejects a trailing '.', so append a zero ("1." -> "1.0").
      _ => double.parse(
        decimal.group(4)!.replaceFirst(_trailingPoint, '.0') +
            (decimal.group(5) ?? ''),
      ),
    };
    return negative ? -value : value;
  }
  final hex = _javaHex.firstMatch(s);
  if (hex != null) {
    final intPart = hex.group(2)!;
    final fracPart = hex.group(3)!;
    if (intPart.isEmpty && fracPart.isEmpty) return null;
    final mantissa = BigInt.parse(
      '0$intPart$fracPart'.replaceFirst(_leadingZeros, ''),
      radix: 16,
    );
    final exponent = int.parse(hex.group(4)!) - 4 * fracPart.length;
    var value = mantissa.toDouble();
    value = exponent >= 0 ? value * _pow2(exponent) : value / _pow2(-exponent);
    return hex.group(1) == '-' ? -value : value;
  }
  return null;
}