In the context of year values how does "aaaa" differ from "yyyy"?

Question

Referring to the SimpleDateFormat docs, the pattern character for representing years is y, so we have representations like yy and yyyy (13, 2013 respectively). That's fine.

When I output the DEFAULT / SHORT / MEDIUM / LONG / FULL patterns for most locales, I get something along these lines:

(EG: New Zealand)

Default: d/MM/yyyy
Short: d/MM/yy
Medium: d/MM/yyyy
Long: d MMMM yyyy
Full: EEEE, d MMMM yyyy

However looking at some locales, eg France, I get this:

Default: j MMM aaaa
Short: jj/MM/aa
Medium: j MMM aaaa
Long: j MMMM aaaa
Full: EEEE j MMMM aaaa

Obviously here aaaa is a representation of the year, but what's the distinction in intent between yyyy and aaaa? IE: why do they use aaaa instead of just yyyy.

Initially I thought it might be something along the lines of French for "[y]ear" is "[a]nnée" (and "[d]ay" is "[j]our", but I see it's also aaaa for Hungarian (and many other locales), and Hungarian for "year" is "év" (day "nap"), so I think the "a" / "année" correlation I'm making is coincidence.

So what is the difference one is supposed to infer here?

I googled about, but drew a blank. Also it might be as obvious as an obvious thing to a Java dev, but I'm just a CFML dev who simply bolts Java into my CFML occasionally when Java does something more expediently than I can do it in native CFML. So sorry if it's a dumb question.

Answer 1

If you look at java.text.DateFormatSymbols you'll find the following field:

/**
 * Localized date-time pattern characters. For example, a locale may
 * wish to use 'u' rather than 'y' to represent years in its date format
 * pattern strings.
 * This string must be exactly 18 characters long, with the index of
 * the characters described by <code>DateFormat.ERA_FIELD</code>,
 * <code>DateFormat.YEAR_FIELD</code>, etc.  Thus, if the string were
 * "Xz...", then localized patterns would use 'X' for era and 'z' for year.
 * @serial
 */
String  localPatternChars = null;

This is a string containing a character for each format element in a predefined order (E.g., character 0 is the Era format character, character 1 is the Year format character, etc).

This field is loaded from the sun.text.resources.FormatData resource bundle (per locale, of course), from the DateTimePatternChars key.

If you examine the sun.text.resources.FormatData_fr resource, you'll find the key-value pair { "DateTimePatternChars", "GaMjkHmsSEDFwWxhKzZ" }.

To make a long story short - the "a" format character in France locale has the exact same effect as the "y" format character in US locale, it's just called differently.