How do I get a random number with a negative number in range? [duplicate]

Question

Consider the following code:

int rand = new Random().nextInt((30 - 20) + 1) + 20

It will return a random number between 30 and 20. However, I need its range to include negative numbers. How would I include negative numbers in the generation?

I have tried using math that would be negative, but that resulted in an error. Simply subtracting or adding the negative numbers would not yield the desired value.

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Sorry, I am only half awake. The correct code is int rand = new Random().nextInt((30 - 20) + 1) + 20;.

Answer 1

To get a random number between a set range with min and max:

int number = random.nextInt(max - min) + min;

It also works with negative numbers.

So:

random.nextInt(30 + 10) - 10;
// max = 30; min = -10;

Will yield a random int between -10 and 30 (exclusive).

It also works with doubles.

Answer 2

You can use Random.nextBoolean() to determine if it's a random positive or negative integer.

int MAX = 30;
Random random = new Random(); // Optionally, you can specify a seed, e.g. timestamp.
int rand = random.nextInt(MAX) * (random .nextBoolean() ? -1 : 1);