Use String.format() for Calendar vs. Date

Question

Why if I use String.format(Date) it prints date in default timezone, but when I use String.format(Calendar) it prints in Calendar's timezone. Actually, the latter is what I need, but can I be sure that this behavior will persist?

Date never has a time-zone and Calendar always does. Is that your doubt? — Peter Lawrey, Oct 16 '12 at 11:44
Check this post: -http://stackoverflow.com/questions/2891361/java-how-to-set-timezone-of-a-java-util-date to know how to set `TimeZone` for your date object. — Rohit Jain, Oct 16 '12 at 11:47
@RohitJain that's impossible, date doesn't contain timezone info. — dhblah, Oct 16 '12 at 12:18
Still, the post Rohit linked to contains your answer: use a `SimpleDateFormat` to format your date and set the timezone on the `SimpleDateFormat` object. — Jesper, Oct 16 '12 at 12:28
Still, I was not asking about `SimpleDateFormat`, but about `String.format()`. — dhblah, Oct 16 '12 at 12:36

score 1 · Accepted Answer · answered Oct 16 '12 at 12:41

As I found from implementation of String.format (at least for JDK 1.5, it has printDateTime(Object, Locale) which contains such code:

    } else if (arg instanceof Date) {
    // Note that the following method uses an instance of the
    // default time zone (TimeZone.getDefaultRef().
    cal = Calendar.getInstance(l);
    cal.setTime((Date)arg);
    } else if (arg instanceof Calendar) {
    cal = (Calendar) ((Calendar)arg).clone();
    cal.setLenient(true);
    } else {

so if argument for String.format is of Date, Calendar.getInstance(Locale) is used, which creates calendar in default timezone, if argument is Calendar then calendar's time zone is used. Moreover, i didn't found any explicit description of this and that method is private, so It's impossible to assume that this behavior won't change.

Use String.format() for Calendar vs. Date

1 Answers1