javaDoubleToString function

String javaDoubleToString(double value)

Formats value exactly as Java's Double.toString(double) (JDK 19+).

JavaRosa uses Java's formatting wherever a number becomes text: XPath string(), calculated values written to the instance, and expression toString(). Dart's own formatting differs (10 vs 10.0, 1e+21 vs 1.0E21), so a direct port would silently change collected data.

Both languages pick the shortest decimal digits that round-trip to the same double, with one difference: Java always considers two significant digits, so when the shortest form has a single digit it uses the closest two-digit decimal instead (4.9E-324, where Dart prints 5e-324). The layout also differs:

• 1e-3 <= |value| < 1e7: plain notation with at least one fraction digit (10.0, 0.001, 9999999.5).
• otherwise: d.dddE±n with at least one fraction digit and no + sign (1.23E21, 1.0E-4).

Implementation

String javaDoubleToString(double value) {
  if (value.isNaN) return 'NaN';
  if (value.isInfinite) return value > 0 ? 'Infinity' : '-Infinity';
  if (value == 0) return value.isNegative ? '-0.0' : '0.0';

  final sign = value < 0 ? '-' : '';
  final magnitude = value.abs();

  // Shortest round-trip digits, e.g. "1.23e+21" or "5e-7".
  var (digits, exponent) = _decompose(magnitude.toStringAsExponential());
  if (digits.length == 1) {
    // Closest two-digit decimal, e.g. "4.9e-324"; then drop a trailing zero.
    (digits, exponent) = _decompose(magnitude.toStringAsPrecision(2));
    if (digits.endsWith('0')) digits = digits.substring(0, 1);
  }

  if (magnitude >= 1e-3 && magnitude < 1e7) {
    final integerDigits = exponent + 1;
    if (integerDigits <= 0) {
      return '${sign}0.${'0' * -integerDigits}$digits';
    }
    if (integerDigits >= digits.length) {
      return '$sign$digits${'0' * (integerDigits - digits.length)}.0';
    }
    return '$sign${digits.substring(0, integerDigits)}.'
        '${digits.substring(integerDigits)}';
  }

  final fraction = digits.length > 1 ? digits.substring(1) : '0';
  return '$sign${digits[0]}.${fraction}E$exponent';
}