Time formatting / SimpleDateFormat

[erictetz]

My application is running an 'elapsed time' counter, which I would
like to display in HH:MM:SS format. My question is how best to do this
in Java. Note, I'm not using the latest version of Java which contains
printf (which makes this trivial).

I'm currently building the string by hand, but it's ugly. I tried
using SimpleDateFormat to do the work for me, but for reasons I don't
understand it adds 16 hours to the output. For example:

Date elapsedTime = Date(0); // 0 seconds elapsed, should be 00:00:00
SimpleDateFormat dateFormat = new SimpleDateFormat("HH:mm:ss");
System.out.println(dateFormat.format(elapsedTime));

This outputs 16:00:00. I have no clue how to get rid of the 16.

What am I doing wrong? Is there a cleaner approach for this?

Cheers,
Eric

 

[Thomas Fritsch]

My application is running an 'elapsed time' counter, which I would
like to display in HH:MM:SS format. My question is how best to do this
in Java. Note, I'm not using the latest version of Java which contains
printf (which makes this trivial).

I'm currently building the string by hand, but it's ugly. I tried
using SimpleDateFormat to do the work for me, but for reasons I don't
understand it adds 16 hours to the output. For example:

Date elapsedTime = Date(0); // 0 seconds elapsed, should be 00:00:00
SimpleDateFormat dateFormat = new SimpleDateFormat("HH:mm:ss");
System.out.println(dateFormat.format(elapsedTime));

This outputs 16:00:00. I have no clue how to get rid of the 16.

See <http://java.sun.com/j2se/1.4.2/docs/api/java/util/Date.html#Date(long)>
The date Date(0) is specified as "January 1, 1970, 00:00:00 GMT", where
"GMT" means London time.
If you live somewhere in America (6 hours west of London), then this
time would be "December 31, 1969, 16:00:00" in your American time zone.
Hence the output would be correct.

What am I doing wrong? Is there a cleaner approach for this?

Normally you won't use this Date(long) constructor, but instead some
other Date constructor or a Calendar method taking
year/month/day[/hour/minute] parameters. They all take your local
timezome into account, so that the problem should disappear.

 

[Lew]

"GMT" means London time.

Only in the winter time do they coincide. Actually it means "the mean solar
time at longitude 0°".
<http://en.wikipedia.org/wiki/Time_zone#Standard_time_zones>
<http://en.wikipedia.org/wiki/UT1>

 

[Thomas Fritsch]

The date Date(0) is specified as "January 1, 1970, 00:00:00 GMT", where
"GMT" means London time.
If you live somewhere in America (6 hours west of London), then this

Aaah, I meant "(8 hours west of London)"
because 16 + 8 = 24.
And yes, Lew is correct: I should say "(8 hours west of longitude 0°)"

 

[Roedy Green]

My application is running an 'elapsed time' counter, which I would
like to display in HH:MM:SS format. My question is how best to do this
in Java. Note, I'm not using the latest version of Java which contains
printf (which makes this trivial).

see http://mindprod.com/jgloss/calendar.html

The problem is you have to pick a timezone. The date itself is in
UTC.

 

[Roedy Green]

Only in the winter time do they coincide. Actually it means "the mean solar
time at longitude 0°".

When you mean standard time, say UTC which has no DST correction ever.
see http://mindprod.com/jgloss/timezone.html