What Java method takes an int and returns +1 or -1?

Question

What Java method takes an int and returns +1 or -1? The criteria for this is whether or not the int is positive or negative. I looked through the documentation but I'm bad at reading it and I can't find it. I know I've seen it somewhere though.

@fortran: The prevailing `signum` answer takes care of that too. — C. K. Young, Mar 11 '10 at 17:27
@Chris and @Halo that's the point, the op wants +1 or -1 on any int, not zero... — fortran, Mar 11 '10 at 17:32
+1 because I had no idea this method existed, though I'm not sure when I would ever use it... — Pops, Mar 11 '10 at 17:33
you do realize that in the time it took you to read the doc, post this question, and wait for the answer, you could have written a function to do exactly what you needed and gone to lunch? — Steven A. Lowe, Mar 11 '10 at 17:41
@steven. that's a good point. I might need it again in the future though in whcih case this will be faster overall. — David, Mar 11 '10 at 17:47
@David: only if you remember the name of the function later ;-) — Steven A. Lowe, Mar 11 '10 at 20:38

score 63 · Accepted Answer · edited Mar 11 '10 at 17:28

63

Integer.signum(int i)

edited Mar 11 '10 at 17:28

Hank Gay

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answered Mar 11 '10 at 17:22

Halo

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can you link me to the relevent documentation – David Mar 11 '10 at 17:23
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thanks. i don't supsoe theres a version that will return 1 when 0 is entered? or do i have to create that myself? – David Mar 11 '10 at 18:06
someone below gave an implementation, I suppose it's true.. you can modify it your way – Halo Mar 11 '10 at 18:09

score 6 · Answer 2 · edited Oct 31 '18 at 17:23

6

Math.signum(value) will do the trick but since it returns float or double (according to parameter) you will have to cast it:

int sign = (int)Math.signum(value);

or:

Integer.signum(value);

edited Oct 31 '18 at 17:23

Neuron

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answered Mar 11 '10 at 17:22

Jack

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score 1 · Answer 3 · edited Aug 04 '16 at 15:56

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Strictly evaluating to -1 or 1, and cooler (probably more efficient too) than n < 0 ? -1: 1:

(n >> 31) | 1

In case you want to use it for long too:

(n >> 63) | 1

edited Aug 04 '16 at 15:56

Klitos Kyriacou

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answered Mar 11 '10 at 18:11

fortran

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score 0 · Answer 4 · edited Dec 01 '17 at 14:45

Math.signum(double i)

Returns the signum function of the argument; zero if the argument is zero, 1.0 if the argument is greater than zero, -1.0 if the argument is less than zero. Special Cases:

If the argument is NaN, then the result is NaN.
If the argument is positive zero or negative zero, then the result is the same as the argument.

Parameters:

d - the floating-point value whose signum is to be returned

Returns: The signum function of the argument

Since: 1.5

Chris Dennett · Answer 5 · 2010-03-11T17:31:38.977

0

Use Integer.signum(int i), but if you want a custom in-line bit of code:

int ans = i < 0 ? -1 : 1;

if you want 0 also:

int ans = i == 0 ? 0 : (i < 0 ? -1 : 1);

edited Mar 11 '10 at 17:31

answered Mar 11 '10 at 17:23

Chris Dennett

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That should be `int ans` for both. – defectivehalt Mar 11 '10 at 17:34
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Don't do this--it's going to make someone pause and think--that's the last thing you want in the middle of analyzing some bug. Make it an external method or break it out into an if (since the number is probably just input to an if statement anyway, it would be much clearer to simply say (if i<0) else if (i > 0) else... – Bill K Mar 11 '10 at 17:55

score -1 · Answer 6 · answered Mar 11 '10 at 17:32

-1

For fun:

return (i > 0) ? 1 : ( (i < 0) ? -1 : 0 );

answered Mar 11 '10 at 17:32

Tom Neyland

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What Java method takes an int and returns +1 or -1?

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