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From: Lew <noone@lewscanon.com>
Newsgroups: comp.lang.java.programmer
Subject: Re: Timezones and versions of Java
Date: Mon, 23 May 2011 11:58:11 -0400
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loial wrote:
> I am trying to convert BST times to EST.

What time zones do you mean here?  Bangladesh Standard Time?  British Summer 
Time?  Eastern Standard Time in the Caribbean?

Neither "EST" nor "BST" is a standard time-zone name.

Have you considered reading the documentation?

> The following code correctly returns a difference of 5 hours between
> the 2 times when run under Java 1.5. :
>
> Local Offset 3600000
> EST Offset -14400000
> EST time Tue May 04 07:48:18 2010

You do realize that Eastern Time is not "EST" on May 4 anywhere other than 
Australia, right?  Any other jurisdiction that uses "EST" as an abbreviation 
is on Summer Time on that date.  Therefore you must be referring to Australian 
time, but that's the wrong offset for that zone.

Please clarify.

In any case, there's nothing correct in what you show here.  Why do you say 
this is a correct return?

> BST time Tue May 04 12:48:18 2010

Does Bangladesh have Daylight Saving Time?

> However if run under Java 1.6 (on the same machine), it returns a time
> difference of 6 hours :
>
> Local Offset 3600000
> EST Offset -18000000
> EST time Tue May 04 06:48:18 2010
> BST time Tue May 04 12:48:18 2010
>
>
> Do I need to do something different in Java 1.6?.

Maybe give it the right time zone?

You do realize that Eastern Standard Time in the U.S. is -18000000 
milliseconds offset from UTC, right?  So if "EST" is "America/New_York" (and, 
of course, not Daylight Saving Time), then this display is correct.

What makes you think that it is not correct?

> Platform is linux [sic].
>
> class testtz {

Class names should start with an upper-case letter.

>      public static void main(String[] args) {
>
>
>         Date date = null;

Why do you set the date to 'null'?  It's unnecessary and potentially harmful; 
it certainly is harmful in the code you show here.

>         SimpleDateFormat dateFormat = new
> SimpleDateFormat("yyyyMMddHHmmss");
>
>         try {
>
>              date = dateFormat.parse("20100504124818");

Here you throw away that 'null' value that you shouldn't have initialized.

>         }
>         catch(ParseException pe) {
>             System.out.println("Error");
>         }
>
>         TimeZone tz1 = TimeZone.getDefault();

If you're in the Northern Hemisphere in most jurisdictions, you will not get 
"EST" from this on May 4.

>         long localOffset = tz1.getOffset(date.getTime());
>
>         System.out.println("Local Offset " + localOffset);
>
>         TimeZone tz2 = TimeZone.getTimeZone("EST");
>
>         long remoteOffset = tz2.getOffset(date.getTime());
>
>         System.out.println("EST Offset " + remoteOffset);
>
>
>         Date dateToPutInDB = new Date(date.getTime() - localOffset +
> remoteOffse;
>
>
>         System.out.println("EST time " + dateToPutInDB)
>
>         System.out.println("BST time " + date);
>
>
>
>     }
>
> }

<http://download.oracle.com/javase/6/docs/api/java/util/TimeZone.html>
"Three-letter time zone IDs

"For compatibility with JDK 1.1.x, some other three-letter time zone IDs (such 
as "PST", "CTT", "AST") are also supported. However, their use is deprecated 
because the same abbreviation is often used for multiple time zones (for 
example, "CST" could be U.S. "Central Standard Time" and "China Standard 
Time"), and the Java platform can then only recognize one of them."

Have you considered reading the documentation?

RTFM.
RTFM.
RTFM.

-- 
Lew
RTFM.