how to convert calendar object to a specific time zone

Question

I am getting date from database from time-zone A (dBDate) and I am getting the current date from my android device I am currently using in time-zone B (deviceNowDate), I need to find the difference between the 2 dates in milli seconds so I think I should convert both of these dates to 1 hardcoded timezone (say timezone C) and then find the difference. How do I convert both of these dates to another time zone?

They are calendar objects.

dbDate.setTimeZone();

will this change the time zone and also convert the date/time for me?

Answer 1

Since the date stored in the database is already in UTC, you can just use the value right away. Or the alternative way is to get a Calendar instance and set the time in milliseconds using setTimeInMillis(long millis).

For the current date & time on the device, invoking Calendar.getInstance() will return a Calendar with device's time zone, date and time.

The getTimeInMillis() will return the UTC milliseconds from epoch, which is independent of the time zone.

Try

long dbMillis = ... // get date value from DB, in UTC already

Calendar cal = Calendar.getInstance(); // get device's date time with
                                       // default device time zone
long now = cal.getTimeInMillis(); // returns device's date time in UTC

long diff = Math.abs(now - dbMillis);