Java date class interesting

Question

End date was being computed to be earlier than the start date

Date startDate = new Date();
Date endDate = new Date(startDate.getTime() + (24 * 3_600_000 * 42));
System.out.println(startDate);
System.out.println(endDate);

output :

Tue Sep 17 01:46:31 EEST 2013
Mon Sep 09 08:43:43 EEST 2013

why the output is not correct ?

Answer 1

Your integer arithmetic has overflowed. The maximum possible value of an int is 2147483647 or Integer.MAX_VALUE (a little over 2 billion), but multiplying your integer literals would yield 3628800000 (about 3.6 billion). The result is a negative number (-666167296), and an earlier date.

Try casting one of your literals as a long to force long arithmetic (or use long literals):

( (long) 24 * 3600000 * 42)

or

(24L * 3600000 * 42)

This operation is well within the range of long values (max value 9223372036854775807, over 9 quintillion).