How to convert a double to an int

Short answer

The (int) cast drops the fractional part:

void main() {
    double price = 9.99;
    int whole = (int) price;
 
    IO.println(whole);
}

Output:

To round to the nearest integer, call Math.round() first. It returns a long, so an int needs one more cast:

void main() {
    double price = 9.99;
    int rounded = (int) Math.round(price);
 
    IO.println(rounded);
}

Output:

Math.toIntExact() throws if the long does not fit into an int:

void main() {
    IO.println(Math.toIntExact(Math.round(1e9)));
    IO.println(Math.toIntExact(Math.round(1e10)));
}

Output:

1000000000
Exception in thread "main" java.lang.ArithmeticException: integer overflow

Casting values that are too large, and NaN. Java does not throw — it silently uses the limit or zero:

void main() {
    IO.println((int) 1e10);
    IO.println((int) Double.NaN);
    IO.println((int) -1e10);
}

Output:

2147483647
0
-2147483648