问公共函数不返回值

EN

GeneralMethods generalMethods = new GeneralMethods();
generalMethods.daysPassed(contacts_update_date, currentDate);

public class GeneralMethods {

    public long daysPassed(String contacts_update_date, String currentDate) {

        // Calculate Time Passed

        long diff;
        long timePassed = 0;

        SimpleDateFormat myFormat = new SimpleDateFormat("dd MM yyyy");
        String inputString1 = contacts_update_date;
        String inputString2 = currentDate;

        try {
            Date date1 = myFormat.parse(inputString1);
            Date date2 = myFormat.parse(inputString2);
            diff = date2.getTime() - date1.getTime();
            timePassed = TimeUnit.DAYS.convert(diff, TimeUnit.MILLISECONDS);

        } catch (ParseException e) {
            e.printStackTrace();
        }

        return timePassed;

    }

}

if (timePassed > 30) { 
//do something 
}