java如何计算两个日期之间相差多少天？

public static void main(String [] args) {
        Date now = new Date();

        Calendar cal = Calendar.getInstance();
        cal.set(2015,2,24);
//        cal.set(Calendar.YEAR, 2015);
//        cal.set(Calendar.MONTH, 2);
//        cal.set(Calendar.DATE, 24);
        long intervalMills = now.getTime() - cal.getTime().getTime();

        long days = intervalMills/(1000*60*60*24);

        System.out.println(days);
    }