java - float number is not the expected number after subtraction

Question

I have the following statement:

float diff = tempVal - m_constraint.getMinVal();

tempVal is declared as a float and the getMinVal() returns a float value.

I have the following print out:

diff=0.099999905, tempVal=5.1, m_constraint.getMinVal()=5.0

I expect the diff is 0.1 but not the above number. how to do that?

Answer 1

Floats use the IEEE754 to represent numbers, and that system has some rounding errors.

Floating point guide

What Every Computer Scientist Should Know About Floating-Point Arithmetic

Wikipedia on IEE754

Bottom-line if you are doing arithmetic and it needs to be exact don't use float or double but us BigDecimal