How to generate random positive and negative numbers in Java

Question

I am trying to generate random integers over the range (-32768, 32767) of the primitive data type short. The java Random object only generates positive numbers. How would I go about randomly creating numbers on that interval? Thanks.

This remind me about Rnd() of VB, it returns value in [0,1) only. — pinichi, Oct 15 '10 at 02:36
Possible duplicate of [How to generate random integers within a specific range in Java?](https://stackoverflow.com/q/363681/608639) — jww, Jan 02 '19 at 17:59

score 58 · Accepted Answer · answered Oct 15 '10 at 02:16

58

You random on (0, 32767+32768) then subtract by 32768

answered Oct 15 '10 at 02:16

pinichi

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score 24 · Answer 2 · answered Jan 10 '13 at 16:04

24

Random random=new Random();
int randomNumber=(random.nextInt(65536)-32768);

answered Jan 10 '13 at 16:04

Truth

466
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scala> def myNextPositiveNumber :Int = { r.nextInt(65536)-32768} myNextPositiveNumber: Int scala> println(myNextPositiveNumber) -17761 scala> println(myNextPositiveNumber) -26558 scala> scala> println(myNextPositiveNumber) -17758 scala> println(myNextPositiveNumber) -823 scala> println(myNextPositiveNumber) 17370 – aironman Feb 21 '17 at 12:06

duggu · Answer 3 · 2013-12-19T04:23:12.153

6

public static int generatRandomPositiveNegitiveValue(int max , int min) {
    //Random rand = new Random();
    int ii = -min + (int) (Math.random() * ((max - (-min)) + 1));
    return ii;
}

edited Dec 19 '13 at 04:23

answered Dec 24 '12 at 12:59

duggu

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Where are you using rand? – WowBow Dec 19 '13 at 04:20
Let's take, for example, min = 2 and max = 4. So in case of lowest random number, let's say 0.001, * ((4 - (- 2)) + 1) = 7 * 0.001 = (int) 0.007 = 0 and then -2 + 0 = -2. So we got -2 when actually the minimum was 2. Something in this formula went wrong. – yoni Jun 21 '15 at 17:40

score 4 · Answer 4 · answered Oct 15 '10 at 02:18

4

Generate numbers between 0 and 65535 then just subtract 32768

answered Oct 15 '10 at 02:18

jcopenha

3,867
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score 3 · Answer 5 · answered Sep 21 '14 at 15:58

3

This is an old question I know but um....

n=n-(n*2)

answered Sep 21 '14 at 15:58

Ethan

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This won't work. 3 = 3 - (3*2), 3 = -6. – sagits Jun 22 '15 at 03:40
1

Wrong. Order of operations. – Ethan Jun 30 '15 at 01:52
Nope, it still wont work. How are you doing the operations? – GelatinFox Jul 10 '15 at 03:02
1

3-(3*2) = 3-(6) = -3 – Ethan Jul 13 '15 at 19:37
What's the point of this? This is just a slow way to write `n = -n`, but with possible overflow in the `n*2`. Does that overflow do something useful? With `n=-32768` we'd get `n = +32768`, which is outside the 2's complement -32768 .. +32767 range. – Peter Cordes Apr 23 '21 at 06:48

score 1 · Answer 6 · answered Mar 21 '16 at 02:43

1

([my double-compatible primitive type here])(Math.random() * [my max value here] * (Math.random() > 0.5 ? 1 : -1))

example:

// need a random number between -500 and +500
long myRandomLong = (long)(Math.random() * 500 * (Math.random() > 0.5 ? 1 : -1));

answered Mar 21 '16 at 02:43

Russ Jackson

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score 0 · Answer 7 · answered Nov 03 '15 at 06:12

0

(Math.floor((Math.random() * 2)) > 0 ? 1 : -1) * Math.floor((Math.random() * 32767))

answered Nov 03 '15 at 06:12

UP209D

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score 0 · Answer 8 · answered Dec 15 '15 at 01:36

In case folks are interested in the double version (note this breaks down if passed MAX_VALUE or MIN_VALUE):

private static final Random generator = new Random();
public static double random(double min, double max) {
    return min + (generator.nextDouble() * (max - min));
 }

How to generate random positive and negative numbers in Java

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