How to manipulate java.util.Date date() from outside the java binary?

I have a java app using date() to obtain the current date, and I'm trying to manipulate the date that it is obtaining from date() for testing purposes.

I've tried setting the system date(on Windows) to a date in the past for example 1/1/2014, but the java app seems to keep getting the realtime date from somewhere other than the system date.

Is it possible to manipulate the date and if so, how can I manipulate the date that the date() function returns from outside the binary?