Problem while calculating time before 5 years

Question

Dear all,
See the following code. Here i tried to calculate the time before 5 years.
import java.util.Date;
public class Test
        public static void main(String args[])
                long threshold = -1;
                long age = 5;
                long currentTime = System.currentTimeMillis();
                threshold = currentTime - (age*(365*86400000)); //  To calculate the time bef 5 years from now.
                System.out.println("Threshold value(in Date) :: "+new Date(threshold));
}The result is
Threshold value(in Date) :: Mon Aug 06 05:42:55 IST 2007
But when i change the code as follows
                threshold = currentTime - (age*365*86400000); // Just removing the brackets before & after 365*86400000It's giving the correct result as follows:
Threshold value(in Date) :: Thu Oct 31 09:12:21 IST 2002
Why is it so?. Please explain me.
Thanks.

Answer 1

the problem is (I believe) due to int overflow.
In your first calculation, your multiplication -- (365*86400000) is done with ints and will give an int result, an incorrect result because this will likely be greater than int allows, which on my system is 2147483647.
the second calculation is a long * int * int, so the result will be a long which will not be corrupted.
Try it yourself:
public class Fubar2
    public static void main(String[] args)
        System.out.println(Integer.MAX_VALUE);
        int a = 100000000;
        int b = 500;
        System.out.println(a * b);
        System.out.println((long)a * b);
        a = 86400000;
        b = 365;
        System.out.println(a * b);
        System.out.println((long)a * b);
}Edited by: petes1234 on Oct 29, 2007 8:53 PM