Question

How come a primitive float value can be -0.0? What does that mean?
Can I cancel that feature?

When I have:

  float fl;  

Then fl == -0.0 returns true and so does fl == 0. But when I print it, it prints -0.0.

Answer 1

Because Java uses the IEEE Standard for Floating-Point Arithmetic (IEEE 754) which defines -0.0 and when it should be used.

The smallest number representable has no 1 bit in the subnormal significand and is called the positive or negative zero as determined by the sign. It actually represents a rounding to zero of numbers in the range between zero and the smallest representable non-zero number of the same sign, which is why it has a sign, and why its reciprocal +Inf or -Inf also has a sign.

You can get around your specific problem by adding 0.0

e.g.

Double.toString(value + 0.0);

See: Java Floating-Point Number Intricacies

Operations Involving Negative Zero
…
(-0.0) + 0.0 -> 0.0

–

“-0.0” is produced when a floating-point operation results in a negative floating-point number so close to 0 that it cannot be represented normally.