Java If a number is -0

Question

If have this code:

double sin = Math.sin(angle*rad);
double cos = Math.cos(angle*rad);
double tan = Math.tan(angle*rad);

It returns the triangle function for a specified angle. However for degrees of angle, like 90, -0.00000 is returned. So when these values are printed out, -0 just looks weird. How would -0 be tested for in an if statement?

I have tried with this code:

if (tan==0) { s.o.p(tan); }

and it doesn't run.

Not an exact duplicate, but see https://stackoverflow.com/q/6724031/2422776 — Mureinik, Oct 16 '18 at 11:36
Where do you get this `-0.00000`? I get `-1.2246467991473532E-16` which is close to 0 but not exactly. — StephaneM, Oct 16 '18 at 11:41
OK, you see -0.0000 because you're formating the result. The result of `System.out.println(Math.tan(Math.PI)); ` is `-1.2246467991473532E-16`. See https://stackoverflow.com/questions/8081827/how-to-compare-two-double-values-in-java — StephaneM, Oct 16 '18 at 11:51

Johan · Accepted Answer · 2018-10-16T18:10:16.247

1

Just take the absolute value on the variable when you compare it with zero. You will likely need to cover a range since it's not always likely to be exactly 0.0.

if (Math.abs(tan) <= threshold) { ... }

Where you set threshold to a small enough value to cover what you consider is close enough to 0.

Edit: Added threshold/epsilon value in comparison - thanks Ben

edited Oct 16 '18 at 18:10

answered Oct 16 '18 at 11:35

Johan

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Which will probably not work because it's not exactly 0 but in a small range around 0. So you probably rather want to define an epsilon so that `Math.abs(tan) < epsilon` – Ben Oct 16 '18 at 11:56
@Ben Good call, I've added it to my answer. Thank you. – Johan Oct 16 '18 at 12:45

score 0 · Answer 2 · answered Oct 17 '18 at 09:12

0

You can check for negative zero by dividing 1 by your value. This will yield Double.POSITIVE_INFINITY for a positive zero and Double.NEGATIVE_INFINITY for a negative zero:

if (1.0 / value == Double.NEGATIVE_INFINITY) {
    // Value was a negative zero
}

answered Oct 17 '18 at 09:12

Erwin Bolwidt

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Java If a number is -0

2 Answers2