# Generate Random Number within a range including negatives?

Andrew Robinson

Greenhorn

Posts: 15

T Dahl

Ranch Hand

Posts: 35

posted 5 years ago

Math.random() is a good place to start. If that doesn't suit your needs, then java.util.Random should be your next stop.

Math.random() generates a double between 0 and 1 (including 0, but not 1). As T Dahl suggested, you can multiply this value by some factor to increase your range, then shift that range by adding or subtracting.

Math.random() generates a double between 0 and 1 (including 0, but not 1). As T Dahl suggested, you can multiply this value by some factor to increase your range, then shift that range by adding or subtracting.

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posted 5 years ago

In general, for any function f that returns a value between a and b, to get a value between c and d apply the following calculation: (f(x) - a) / (b - a) * (d - c) + c.

The subtraction of a gives you a value between 0 and (b - a).

The dividing by (b - a) gives you a value between 0 and 1 (provided b != a).

The multiplication gives you a value between 0 and (d - c).

The addition of c gives you a value between c and d.

In this case, a == 0 and b == 1, so you are left with Math.random() * (d - c) + c.

The subtraction of a gives you a value between 0 and (b - a).

The dividing by (b - a) gives you a value between 0 and 1 (provided b != a).

The multiplication gives you a value between 0 and (d - c).

The addition of c gives you a value between c and d.

In this case, a == 0 and b == 1, so you are left with Math.random() * (d - c) + c.

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