Java convert date to EST/EDT timezone

Java supports three timezone constants for Eastern Standard Time i.e. "EST", "America/New_York" and "EST5EDT". It is very important to understand difference between them to correctly utilize these constants for converting date or time in Eastern Standard Time values.

1. Difference between EST, EST5EDT and ‘America/New_York’

In eastern part of the USA, timezone offsets are different during summer and winter.

1. During winter, time is EST. EST is always UTC-5 hours and without consideration for DST (daylight savings time).
2. During summer, time is EDT. EDT is UTC-4 hours and with DST.
3. To correctly represent time, during whole year, you should call it ET (Eastern Time) which include EST and EDT both.
4. From timezone perspective, EST5EDT means either in EST or EDT. It specifies that the zone uses a standard time of UT-5h called “EST”, a DST of UT-4h called “EDT”, and switches between them annually on.
5. The time zone America/New_York is the same as EST5EDT for all dates after the ‘Uniform Time Act of 1966‘.
6. So if you are not using dates before 1966 in your application, then you should use America/New_York timezone. It is preferred way.

Always, prefer to use 'America/New_York' for Eastern time. And use ‘ET’ in formatted timestamp. It represents EST and EDT both.

2. Convert timestamp to ET timezone

Java program to convert date to EST or EDT timezones.

2.1. LocalDateTime [JDK-Version >= Java 8]

import java.time.LocalDateTime;
import java.time.ZoneId;
import java.time.ZonedDateTime;
import java.time.format.DateTimeFormatter;

public class Main 
{
	static DateTimeFormatter globalFormat = DateTimeFormatter.ofPattern("MM/dd/yyyy 'at' hh:mma z");
	static DateTimeFormatter etFormat = DateTimeFormatter.ofPattern("MM/dd/yyyy 'at' hh:mma 'ET'");
	
	static ZoneId istZoneId = ZoneId.of("Asia/Kolkata");
	static ZoneId etZoneId = ZoneId.of("America/New_York");
	
	public static void main(String[] args) 
	{		
		LocalDateTime currentDateTime = LocalDateTime.now();
		
		ZonedDateTime currentISTime = currentDateTime.atZone(istZoneId);				//India Time
		ZonedDateTime currentETime = currentISTime.withZoneSameInstant(etZoneId);		//ET Time
		
		System.out.println(globalFormat.format(currentISTime));
		System.out.println(etFormat.format(currentETime));
	}
}

Watch the output:

07/13/2018 at 03:07PM IST
07/13/2018 at 05:37AM ET

2.2. Date and Calendar [JDK-Version < Java 8]

import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;
import java.util.TimeZone;

public class Main 
{
	static SimpleDateFormat istDf = new SimpleDateFormat("MM/dd/yyyy 'at' hh:mma z");
	static SimpleDateFormat etDf = new SimpleDateFormat("MM/dd/yyyy 'at' hh:mma 'ET'");

	static TimeZone etTimeZone = TimeZone.getTimeZone("America/New_York");
	
	static {
		//Set ET timezone
		etDf.setTimeZone( etTimeZone );
	}
	
	public static void main(String[] args) 
	{
		Date currentDate = new Date();
		Calendar currentTime = Calendar.getInstance();
		
		//In India Time
		System.out.println(istDf.format(currentDate.getTime()));
		System.out.println(istDf.format(currentTime.getTimeInMillis()));
		
		//In ET Time
		System.out.println(etDf.format(currentDate.getTime()));
		System.out.println(etDf.format(currentTime.getTimeInMillis()));
	}
}

Watch the output:

07/13/2018 at 02:34PM IST
07/13/2018 at 02:34PM IST

07/13/2018 at 05:04AM ET
07/13/2018 at 05:04AM ET

Drop me your questions in comments section regarding convert date to EST in Java.

Happy Learning !!

Ref:

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