[SOLVED] Difference in initialization of a Locale object

Difference in initialization of a Locale object

Is there any difference between this two ways of creating a Locale :

Locale uk    = Locale.UK;

Locale en_uk = new Locale("en", "UK");

The only difference I have noticed so far is that getDisplayCountry returns different values. The first United Kingdom and the second UK , which does not bother me very much. Is there besides that any difference? Especially because I would like to adopt the first style for other regions like Germany, France, Korea etc

Solution

tl;dr

Wrong country code.
Do not use Locale constants. Use Locale.of.

Locale.of( "en" , "GB" )  // For English language, and cultural norms of United Kingdom.

Other examples:

Locale.of( "en" , "CA" ) for English in Canada.
Locale.of( "fr" , "CA" ) for French in Canada.
Locale.of( "en" , "US" ) for English in United States.

`GB`, not `UK`

For your purpose, the correct country code for the United Kingdom of Great Britain and Northern Ireland is GB, not UK, as commented by Mark Rotteveel.

CLDR

Modern Java (9+) uses by default the Common Locale Data Repository (CLDR) as the primary source of localization data. Entry # 827 in the CLDR shows a country code of GB for United Kingdom.

Standard country codes

The Javadoc for Locale states that the country/region code must be either:

ISO 3166 alpha-2 country code, or …
UN M.49 numeric-3 area code.

If curious, dump to console:

Arrays.stream( Locale.getISOLanguages() ).forEach( System.out::println );  // All 2-letter country codes defined in ISO 3166.
Arrays.stream( Locale.getISOCountries() ).forEach( System.out::println );  // All 2-letter language codes defined in ISO 639.

The Javadoc also notes that a complete list can be found in the IANA Language Subtag Registry with a tip to search for Type: region. There we find this entry telling us to use GB for the United Kingdom.

%%
Type: region
Subtag: GB
Description: United Kingdom
Added: 2005-10-16
Comments: as of 2006-03-29 GB no longer includes the Channel Islands and
  Isle of Man; see GG, JE, IM
%%

Validator

The Comment by andrewJames points us to this online validator by Christoph Schneegans for IETF BCP 47 language tag with language and country code combined.

There we see en-UK fails, while en-GB passes.

Avoid `Locale` constants

You should ignore those constants defined on Locale class such as Locale.UK and Locale.CANADA_FRENCH. Their creation was a hasty poor decision in design. For more info, see my longer Answer.

Instead, in modern Java (19+), use the convenient static factory methods Locale.of.

`Locale.UK`, Locale.of( "en" , "GB" )

See Locale.of in action.

Locale locale = Locale.of( "en" , "GB" ) ;