Why doesn't (int) Math.random()*10 produce 10 in Java?

Question

Why the following produce between 0 - 9 and not 10?

My understanding is Math.random() create number between 0 to under 1.0.

So it can produce 0.99987 which becomes 10 by *10, isn't it?

int targetNumber = (int) (Math.random()* 10);

Answer 1

Casting a double to an int in Java does integer truncation. This means that if your random number is 0.99987, then multiplying by 10 gives 9.9987, and integer truncation gives 9.

Answer 2

From the Math javadoc :

"a pseudorandom double greater than or equal to 0.0 and less than 1.0"

1.0 is not a posible value with Math.random. So you can't obtain 10. And (int) 9.999 gives 9

Answer 3

Cause (Math.random()* 10 gets rounded down using int(), so int(9.9999999) yields 9.