RFR: 8282819: Deprecate Locale class constructors

[Naoto Sato]

On Fri, 25 Mar 2022 15:37:36 GMT, Roger Riggs <rriggs at openjdk.org> wrote:

>> Proposing to deprecate the constructors in the `java.util.Locale` class. There is already a factory method and a builder to return singletons, so there is no need to have constructors anymore unless one purposefully wants to create `ill-formed` Locale objects, which is discouraged. We cannot terminally deprecate those constructors for the compatibility to serialized objects created with older JDKs. Please see the draft CSR for more detail.
>
> src/java.base/share/classes/java/util/Locale.java line 245:
> 
>> 243:  * <h4>Factory Method</h4>
>> 244:  *
>> 245:  * <p>The method {@link #forLanguageTag} obtains a {@code Locale}
> 
> The factory name `forLanguageTag` is a bit off-putting, it doesn't seem like the best name for the factory.
> Yes, it already exists and does what's required but you might get better uptake with a more natural name.
> 
> Some alternatives:
>  - `Locale.of("en_US")` - short and conventional
>  - `Locale.ofLanguage("en_US")` - 'of' prefix is used in other factories
>  - `Locale.forLanguage("en_US")` - natural but less conventional

I was thinking of a *new* factory method, along the line with Stuart's suggestion, something like this:

Locale.of(String... elements)

where elements can either `(lang)`, `(lang, ctry)`, `(lang, ctry, vrnt)`, or `(lang, ctry, vrnt, scpt)`. Either element can be an empty string, but cannot be null. These elements are *not* language tags, but conventional arguments to constructors, so it is compatible (and works as a stop-gap) to the old constructors. This way third parties will not have to deal with the boilerplate code mentioned above on migration.

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PR: https://git.openjdk.java.net/jdk/pull/7947