Search code examples
javaandroidandroid-calendartimezone-offsetjava.util.calendar

How can I change the Calendar Offset?

I need to change Calendar timezone offset

I tried many thing;

1-

Calendar calendar = Calendar.getInstance();
calendar.setTimeInMillis(TimeUnit.HOURS.convert(rawOffset, TimeUnit.MILLISECONDS) + 
System.currentTimeMillis());

2-

TimeZone timezone = new SimpleTimeZone();
timezone.setRawOffset(rawOffset);

Calendar calendar = Calendar.getInstance();
calendar.setTimeZone(timezone);

Our API returning +1.0 timezone (Berlin) But I can't change Calender timezone offset. How can change?

Solution

  • java.time and ThreeTenABP

    Don’t mingle with raw offsets. Java knows the offset for Berlin better than you. And consider not using Calendar. That class has a number of design problems and is considered long outdated.

        ZonedDateTime zdtBerlin = ZonedDateTime.now(ZoneId.of("Europe/Berlin"));
    System.out.println("Zeit in Berlin: " + zdtBerlin);

    When I ran this snippet just now, I got this output:

    Zeit in Berlin: 2019-02-08T19:23:00.275+01:00[Europe/Berlin]

    As the name says, a ZonedDateTime has a time zone in it. In this case Europe/Berlin. It’s the modern replacement for GregorianCalendar (the most common concrete subclass of the abstract Calendar class).

    Question: Can I use java.time on Android?

    Yes, java.time works nicely on older and newer Android devices. It just requires at least Java 6.

    • In Java 8 and later and on newer Android devices (from API level 26) the modern API comes built-in.
    • In Java 6 and 7 get the ThreeTen Backport, the backport of the modern classes (ThreeTen for JSR 310; see the links at the bottom).
    • On (older) Android use the Android edition of ThreeTen Backport. It’s called ThreeTenABP. And make sure you import the date and time classes from org.threeten.bp with subpackages.

    What went wrong in your code?

    Snippet 1-: You are setting the Calendar’s time to an hour into the future. You are not setting the time zone.

    Snippet 2-: First SimpleTimeZone hasn’t got a no-arg constructor, so new SimpleTimeZone() won’t work. Next, its setRawOffset expects an offset in milliseconds. If rawOffset is 1, you are setting an offset of 1 millisecond.

    Links