I'm trying to convert a millisecond time (milliseconds since Jan 1 1970) to a time in UTC in Java. I've seen a lot of other questions that utilize SimpleDateFormat to change the timezone, but I'm not sure how to get the time into a SimpleDateFormat, so far I've only figured out how to get it into a string or a date.

So for instance if my initial time value is 1427723278405, I can get that to Mon Mar 30 09:48:45 EDT using either `String date = new SimpleDateFormat("MMM dd hh:mm:ss z yyyy", Locale.ENGLISH).format(new Date (epoch));` or `Date d = new Date(epoch);` but whenever I try to change it to a SimpleDateFormat to do something like [this](https://stackoverflow.com/questions/2891361/how-to-set-time-zone-of-a-java-util-date) I encounter issues because I'm not sure of a way to convert the Date or String to a DateFormat and change the timezone. 

If anyone has a way to do this I would greatly appreciate the help, thanks!