Converting double value of 1234567.1234 to float in java

Question

I am trying to convert double to float in java.

Double d = 1234567.1234;
Float f = d.floatValue();

I see that the value of f is

1234567.1

I am not trying to print a string value of float. I just wonder what is the maximum number of digits not to lose any precision when converting double to float. Can i show more than 8 significant digits in java?

Answer 1

float: 32 bits (4 bytes) where 23 bits are used for the mantissa (6 to 9 decimal digits, about 7 on average). 8 bits are used for the exponent, so a float can “move” the decimal point to the right or to the left using those 8 bits. Doing so avoids storing lots of zeros in the mantissa as in 0.0000003 (3 × 10^-7) or 3000000 (3 × 10⁷). There is 1 bit used as the sign bit.

double: 64 bits (8 bytes) where 52 bits are used for the mantissa (15 to 17 decimal digits, about 16 on average). 11 bits are used for the exponent and 1 bit is the sign bit.

I believe you hit this limit what cause that problem.

If you change

Double d = 123456789.1234;
Float f = d.floatValue();

You will see that float value will be 1.23456792E8