Android how to get time difference between two time zones in android?

Question

I need to get time difference between two dates in different time zones. Currently I am doing this:

Calendar c1=Calendar.getInstance(TimeZone.getTimeZone("EDT"));
Calendar c2=Calendar.getInstance(TimeZone.getTimeZone("GMT"));
String diff=((c2.getTimeInMillis()-c1.getTimeInMillis())/(1000*60*60))+" hours";
new AlertDialog.Builder(this).setMessage(diff).create().show();

I get 0 hours. What am I doing wrong?

Answer 1

getTimeInMillis() returns the number of milliseconds since the epoch in UTC. In other words, the time zone is irrelevant to it.

I suspect you actually want:

long currentTime = System.currentTimeMillis();
int edtOffset = TimeZone.getTimeZone("EDT").getOffset(currentTime);
int gmtOffset = TimeZone.getTimeZone("GMT").getOffset(currentTime);
int hourDifference = (gmtOffset - edtOffset) / (1000 * 60 * 60);
String diff = hourDifference + " hours";

Answer 2

Jon is close, but due to character restrictions I can't edit his answer. This is the same code but with "EDT" changed to "EST" for Eastern Standard Time.

long currentTime = System.currentTimeMillis();
int edtOffset = TimeZone.getTimeZone("EST").getOffset(currentTime);
int gmtOffset = TimeZone.getTimeZone("GMT").getOffset(currentTime);
int hourDifference = (gmtOffset - edtOffset) / (1000 * 60 * 60);
String diff = hourDifference + " hours";

But this solution makes a major assumption that TimeZone.getAvailableIDs() has within it's string array both "EST" and "GMT". If that method doesn't contain those timezone strings it will come back as 0 offset.