According to this site :
SimpleDateFormat, the first time you try parsing (or, presumably,
formatting) a date, will load in all the timezone data for your
locale. This will take 2-3 seconds. It is hoped that this will be
fixed in some future edition of Android.
In the interim, consider using AsyncTask to "warm up" SimpleDateFormat
in your process before you need it. Just parse some date in the
AsyncTask doInBackground() to get it to load the timezones sometime
when it will not impact the user so much. Once initialized in your
process, SimpleDateFormat will run quickly until your process is
terminated.
There is an open issue and you can find an explanation :
This is due to the lazy initialization of the timezone zone strings.
Only the first call will take this long. If the SimpleDateFormat is
used again afterwards it's loaded from cache and shouldn't take that
long anymore.
Before this was changed it was done when the class was loaded and thus
the start of an activity took those 2-3 seconds longer. This had a
much worse impact on the user experience than if it takes those
seconds when it's actually used the first time. The problem is that
there's no way right now to circumvent this issue due to the design of
the SimpleDateFormat api. Only faster phones might fix this by just
taking less time to collect those strings.
The caching happens in the DateFormatSymbols that SimpleDateFormat is
using. By reusing that instance it's possible to only have to load the
stings once (for the same loale). You could also create that Instance
in a thread at the startup of the activity so that it's already cached
once it's used. To init the strings just call .hashCode() which does
force initialize the cache. A bit faster but less simple would be to
serialize the instance. This also forces the cache to be initialized.
Since this happens only the first time your function is called (due to the initialization of the timezone strings), I would recommend (as they said) to use an AsyncTask
to "pre-load" the SimpleDateFormat
. I think it will fix your problem.