Question

I have two objects, p4 and p5, that have a Date property. At some points, the constructor works fine:

p4.setClickDate(new Date(System.currentTimeMillis() - 86400000 * 4));

Sets the date to Sun Jul 31 11:01:39 EDT 2011

And in other situations it does not:

p5.setClickDate(new Date(System.currentTimeMillis() - 86400000 * 70));

Sets the date to Fri Jul 15 04:04:26 EDT 2011

By my calculations, this should set the date back 70 days, no?

I can get around this using Calendar, but I’m curious as to why Date behaves this way.

Thanks!

Answer 1

That’s caused by an integer overflow. Integers have a maximum value of Integer.MAX_VALUE which is 2147483647. You need to explicitly specify the number to be long by suffixing it with L.

p5.setClickDate(new Date(System.currentTimeMillis() - 86400000L * 70));

You can see it yourself by comparing the results of

System.out.println(86400000 * 70); // 1753032704
System.out.println(86400000L * 70); // 6048000000

See also:

• Java Tutorials – Language Basics – Primitive Data Types