Why Does `SimpleDateFormat` Return 2012 for 'Y' and 2011 for 'y'?

Why 'Y' Returns 2012 While 'y' Returns 2011 in SimpleDateFormat

In the SimpleDateFormat class, 'Y' and 'y' represent different concepts in the context of week years and years.

Week Year ('Y')

A week year aligns with the week of year cycle, where all weeks between the first and last weeks have the same week year value. This means that the first and last days of a week year may have different calendar year values.

Year ('y')

The year ('y') represents the calendar year according to the specific calendar system being used.

In the example provided:

System.out.println(new SimpleDateFormat("Y").format(new Date())); // prints 2012
System.out.println(new SimpleDateFormat("y").format(new Date())); // prints 2011

'Y' returns 2012 because the current date is part of week 1 of 2012, even though the calendar year is still 2011. This is due to the specific configuration of the SimpleDateFormat instance, which may be configured to follow the ISO 8601 standard.

'y' returns 2011 because it represents the calendar year, which is still 2011, regardless of the week year.

Therefore, 'Y' and 'y' provide different information based on whether you need the week year or the calendar year.

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