Use JodaTime for this. It is much better than the standard Java DateTime Apis. Here is the code in JodaTime for calculating difference in days:
private static void dateDiff() {
System.out.println("Calculate difference between two dates");
System.out.println("=================================================================");
DateTime startDate = new DateTime(2000, 1, 19, 0, 0, 0, 0);
DateTime endDate = new DateTime();
Days d = Days.daysBetween(startDate, endDate);
int days = d.getDays();
System.out.println(" Difference between " + endDate);
System.out.println(" and " + startDate + " is " + days + " days.");
}