Time operations day difference

Question

hi , � have to subruct two days like 13/08/07 03/08/07 and result must be
10 �. at my program � have dates as string '20070102' yyyyddmm
first � am converting them to date
     public Date toDate(String dateString){
          int year = Integer.parseInt(dateString.substring(0,4));
          int month = Integer.parseInt(dateString.substring(4,6));
          int day = Integer.parseInt(dateString.substring(6,8));
          Calendar c1 = Calendar.getInstance();
          c1.set(year,month,day);
          SimpleDateFormat sdf = new SimpleDateFormat("dd.MM.yy");
          return c1.getTime();
then subsructing two dates
using this function
     public int dateDifference(Date d1, Date d2){
          int days=0;
          Calendar c1 = Calendar.getInstance();
          Calendar c2 = Calendar.getInstance();
          c1.setTime(d1);
          c2.setTime(d2);
          long first = c2.getTime().getTime();
          long second = c1.getTime().getTime();
          long result = (first - second) /(24*3600*1000);
          days = (int) result;
          return days;
but somethings going wrong like difference between x and y not always z it s for ex '20070113'-'20070101' = 12 but '20070108'-'20070101' = 6
how can it be.
thnks.

Answer 1

public class Diff
    public static void printDiff(String sdate1, String sdate2, String fmt, TimeZone tz)
        SimpleDateFormat df = new SimpleDateFormat(fmt);
        Date date1  = null;
        Date date2  = null;
        try
            date1 = df.parse(sdate1);
            date2 = df.parse(sdate2);
        catch (ParseException pe)
            pe.printStackTrace();
        Calendar cal1 = null;
        Calendar cal2 = null;
        if (tz == null)
          cal1=Calendar.getInstance();
          cal2=Calendar.getInstance();
        else
          cal1=Calendar.getInstance(tz);
          cal2=Calendar.getInstance(tz);
        // different date might have different offset
        cal1.setTime(date1);         
        long ldate1 = date1.getTime() + cal1.get(Calendar.ZONE_OFFSET) + cal1.get(Calendar.DST_OFFSET);
        cal2.setTime(date2);
        long ldate2 = date2.getTime() + cal2.get(Calendar.ZONE_OFFSET) + cal2.get(Calendar.DST_OFFSET);
        // Use integer calculation, truncate the decimals
        int hr1   = (int)(ldate1/3600000); //60*60*1000
        int hr2   = (int)(ldate2/3600000);
        int days1 = (int)hr1/24;
        int days2 = (int)hr2/24;
        int dateDiff  = days2 - days1;
        int weekOffset = (cal2.get(Calendar.DAY_OF_WEEK) - cal1.get(Calendar.DAY_OF_WEEK))<0 ? 1 : 0;
        int weekDiff  = dateDiff/7 + weekOffset;
        int yearDiff  = cal2.get(Calendar.YEAR) - cal1.get(Calendar.YEAR);
        int monthDiff = yearDiff * 12 + cal2.get(Calendar.MONTH) - cal1.get(Calendar.MONTH);
        System.out.println(); 
        System.out.println("DateTime 1: " + sdate1);
        System.out.println("DateTime 2: " + sdate2);
        System.out.println("Date difference : " + dateDiff);
        System.out.println("Week difference : " + weekDiff);
        System.out.println("Month difference: " + monthDiff);
        System.out.println("Year difference : " + yearDiff);       
    public static void main(String[] args)
        String fmt    = null;
        String sdate1 = null;
        String sdate2 = null;
        fmt    = "MM-dd-yyyy HH:mm:ss";
        sdate1 = "12-31-2002 23:59:59";
        sdate2 = "01-01-2003 00:00:01";
        // Result is independent of format
        // null will print in local timezone
        // Print out 1 day, i month, 1 year difference
        System.out.println("In your local time:"); 
        printDiff(sdate1, sdate2, fmt, null);
        // Beijing timezone, if you are not in +8 timezone, the resuls are all 0's
        System.out.println("In Beijing time:"); 
        printDiff(sdate1, sdate2, fmt, TimeZone.getTimeZone("GMT+08:00"));
        // for testing the weekDiff
        fmt    = "MM-dd-yyyy HH:mm:ss";
        sdate1 = "12-31-2002 23:59:59";
        sdate2 = "01-06-2003 00:00:01";
        System.out.println("In your local time:"); 
        printDiff(sdate1, sdate2, fmt, null);
        fmt    = "MM-dd-yyyy HH:mm:ss";
        sdate1 = "01-04-2003 23:59:59";
        sdate2 = "01-05-2003 00:00:01";
        System.out.println("In your local time:"); 
        printDiff(sdate1, sdate2, fmt, null);
        // something interesting here
        fmt    = "MM-dd-yyyy HH:mm:ss";
        sdate1 = "12-31-1996 23:59:59";
        sdate2 = "01-01-1997 00:00:01";
        System.out.println("In your local time:"); 
        printDiff(sdate1, sdate2, fmt, null);
}