SimpleDateFormat("EEEE") Returns Wrong Day of Week for Timezone

Question

I have the following simple code to get the Day of week according to a timezone.

Calendar calendar = Calendar.getInstance(TimeZone.getTimeZone(details.getTimezone()));
String dayOfWeek = new SimpleDateFormat("EEEE").format(calendar.get(Calendar.DAY_OF_WEEK));

Here, the details.getTimezone() returns an acceptable value such as "Asia/Kolkata" and the calendar.get(Calendar.DAY_OF_WEEK) returns the correct value 6.

According to the sequence, day 6 should return "Friday", but this function returns "Thursday" instead.

Please let me know if I am doing anything wrong.

Also let me know if I'm correct in understanding that DAY_OF_WEEK = 6 means Friday.

Answer 1

java.time

The java.util Date-Time API and their formatting API, SimpleDateFormat are outdated and error-prone. It is recommended to stop using them completely and switch to the modern Date-Time API^*.

Solution using java.time, the modern API:

import java.time.ZoneId;
import java.time.ZonedDateTime;
import java.time.format.DateTimeFormatter;
import java.util.Locale;

public class Main {
    public static void main(String[] args) {
        ZonedDateTime zdt = ZonedDateTime.now(ZoneId.of("Asia/Kolkata"));
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("EEEE", Locale.ENGLISH);
        System.out.println(dtf.format(zdt));
    }
}

Output:

Friday

Learn more about java.time, the modern Date-Time API^* from Trail: Date Time.

Using legacy API:

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;
import java.util.TimeZone;

public class Main {
    public static void main(String[] args) {
        Date date = new Date();
        DateFormat sdf = new SimpleDateFormat("EEEE", Locale.ENGLISH);
        sdf.setTimeZone(TimeZone.getTimeZone("Asia/Kolkata"));
        System.out.println(sdf.format(date));
    }
}

Output:

Friday

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^{* For any reason, if you have to stick to Java 6 or Java 7, you can use ThreeTen-Backport which backports most of the java.time functionality to Java 6 & 7. If you are working for an Android project and your Android API level is still not compliant with Java-8, check Java 8+ APIs available through desugaring and How to use ThreeTenABP in Android Project.}