Axim Axim - 2 months ago 14
Java Question

How do I check for a negative zero in Java 8?

I've been trying to figure out how to determine if a double value is

-0.0d
. I googled the problem for a bit and found a few different approaches, however all the threads I found were at least a couple years old and seem to no longer work.

Here's what I've tried so far:

double x, y;
x = 0;
y = -0;

println(x == y);
println(Double.compare(x, y) == 0);
println(new Double(x).equals(new Double(y)));
println(Double.doubleToLongBits(x) == Double.doubleToLongBits(y));
println(Math.signum(x) == Math.signum(y));


All of those print
true
, unfortunately.

The reason I need to distinguish between 0 and -0, if you're wondering, is because I'm trying to parse a double value from user input, and using -0 as a sentinel value in case of an exception.

Answer

Your problem is that you are using y = -0 instead of y = -0.0. 0 is and integer literal and there is no -0 int value, it just stays 0 and then is widened to +0.0d. You could also use -(double)0 to do the widening before the negation and get the same result as -0.0.