CODEWITHSUNDEEP
javac#timestamp-with-timezone
user3644708
user3644708

Reputation: 2495

C# DateTime in Java

I am trying to convert millseconds to time in Java.

when I do this in C#

DateTime EpochOrigin = new DateTime(1970, 1, 1, 0, 0, 0, 0);

Console.WriteLine("1406205185123 = " + EpochOrigin.AddMilliseconds(1406205185123));

result 24/07/2014 12:33:05

when I do same in Java

 Calendar cc = new GregorianCalendar();

cc.setTimeInMillis(1406205185123L);

result Thu Jul 24 13:33:05 BST 2014

The Java result add 1 more hour than C# .

Any suggestion how can I fix this?

Upvotes: 2

Views: 2248

Answers (3)

user3644708
user3644708

Reputation: 2495

thank you for your replies and answers. I find out why:

both C# and Java aware of the time zone.

because c# did this

DateTime EpochOrigin = new DateTime(1970, 1, 1, 0, 0, 0, 0);
EpochOrigin.AddMilliseconds(1406205185123)

in Java, it should be

Calendar cal = Calendar.getInstance();
cal.set(1970, 0, 1, 0, 0, 0);
cal.set(Calendar.MILLISECOND, 0);
long result = cal.getTimeInMillis();
long value = result + 1406205185123;
return new Timestamp(value);

Upvotes: 0

lmillefiori
lmillefiori

Reputation: 486

In C# DateTime doesn't store time zone information, but has a Kind property whose value indicates whether the time represented by this instance is based on local time, Coordinated Universal Time (UTC), or neithee (see MSDN). The default value of DateTime.Kind property is Unspecified. Therefore, in your C# code, a DateTime structure created with the line 

DateTime origin = new DateTime(1970, 1, 1, 0, 0, 0, 0);

should definitely be created in this way: 

DateTime origin = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);

in order to be used as the reference time for the conversion (Epoch time origin is January 1, 1970, 00:00 UTC).

More information can be found in this previous question: https://stackoverflow.com/a/2883645/1236452.

Edit 1

A quick remark: DateTime in C# is somehow aware of the time zone (my local time is GMT+1)(edit: please refer to comments and Edit 2): 

DateTime t = new DateTime(1970,1,1,0,0,0);
Console.WriteLine(t.ToLocalTime());      // 01/01/1970 01:00:00 (GMT+1)
Console.WriteLine(t.ToUniversalTime());  // 31/12/1969 23:00:00 (GMT)

Edit 2

As correctly pointed out in the comments, DateTime is not aware of the time zone in the sense that it holds the time zone information. However, in its Kind property it does store a value that indicates whether the instance is based on local time or UTC, as stated in the documentation:

DateTime.Kind Property: Gets a value that indicates whether the time represented by this instance is based on local time, Coordinated Universal Time (UTC), or neither. [...]

The Kind property allows a DateTime value to clearly reflect either Coordinated Universal Time (UTC) or the local time. In contrast, the DateTimeOffset structure can unambiguously reflect any time in any time zone as a single point in time.

Upvotes: 2

Mateusz
Mateusz

Reputation: 2317

As you can see result in Java has BST mark which tells that it is in British summer time. So GregorianCalendar takes your time zone into account.

DateTime in C# is not aware of time zone so it is UTC because unix epoch is UTC and if you add miliseconds to UTC time you will get UTC time as well.

Upvotes: 2

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