Question

A String representation of a double is written to and read from a file by a C# application.

The C# application converts the double to a string using the following fragment:

value.ToString("R", NumberFormatInfo.InvariantInfo);

The C# application converts the string to a double using the following fragment

double num = double.Parse(s, NumberStyles.Float, (IFormatProvider) NumberFormatInfo.InvariantInfo);

If that same file were to be written to and read from by a Java application, how would you go about converting the types without losing data?

Answer 1

Just using Double.parseDouble() and Double.toString() should work without losing data, I believe. In particular, from the docs for Double.toString():

How many digits must be printed for
the fractional part of m or a? There
must be at least one digit to
represent the fractional part, and
beyond that as many, but only as many,
more digits as are needed to uniquely
distinguish the argument value from
adjacent values of type double. That
is, suppose that x is the exact
mathematical value represented by the
decimal representation produced by
this method for a finite nonzero
argument d. Then d must be the double
value nearest to x; or if two double
values are equally close to x, then d
must be one of them and the least
significant bit of the significand of
d must be 0.

Another alternative, if you want to preserve the exact string representation (which isn’t quite the same thing) is to use BigDecimal in Java.