How to change the precision of a float conversion?

Question

I am trying to convert float value to 32 bit unsigned long value and facing the problem of loss of value. long v = (long) f;

Here when f is 4294967295 ((2^32) -1). The conversion to long returns 4294967296 instead of 4294967295 because float conversion is precised to 7 decimal places. I need precision to 9 decimal places. Is there any way to achieve this?

Answer 1

Quote from Java Puzzlers: Traps, Pitfalls, and Corner Cases book:

Floating-point operations return the floating-point value that is closest to their exact mathematical result. Once the distance between adjacent floating-point values is greater than 2, adding 1 to a floating-point value will have no effect, because the half-way point between values won't be reached. For the float type, the least magnitude beyond which adding 1 will have no effect is 2^25, or 33,554,432; for the double type, it is 2^54, or approximately 1.8 × 10^16.

So basicly, if you want to represent big numbers, float is a bad idea. Above 2^25 it is not able to represent at least every other integer. It get worse the bigger the number gets.

The best option for you would be to use BigDecimal instead.