[sealed-classes] Spec for next version of Sealed Classes

Gavin Bierman gavin.bierman at oracle.com
Wed Nov 4 17:50:23 UTC 2020

The permanent location for this spec is now:

http://cr.openjdk.java.net/~gbierman/jep397/latest/ <http://cr.openjdk.java.net/~gbierman/jep397/latest/>

(I have fixed the two issues that Chris spotted [1].)

Comments still welcome!


[1] http://mail.openjdk.java.net/pipermail/amber-spec-experts/2020-October/002624.html

> On 23 Oct 2020, at 16:16, Gavin Bierman <gavin.bierman at oracle.com> wrote:
> Dear all:
> Drafts of the specs for the Sealed Classes feature that we plan to preview for
> a second time in JDK 16 are now available:
> http://cr.openjdk.java.net/~gbierman/8246775/latest/
> [NB: The URL will change once we have a JEP number, and will be announced.]
> The changes are the same as those in the first preview that was released in Java
> SE 15, except for minor editorial changes and the following:
> - Clarification the use of context when applying the lexical grammar,
>  particularly in the identification of contextual keywords (formerly described
>  as "restricted identifiers" and "restricted keywords"). This is detailed in a
>  companion document entitled “Contextual Keywords". The keywords `sealed`,
>  `non-sealed`, and `permits` are now defined as new instances of contextual
>  keywords (3.9). 
> - This spec now assumes that the changes detailed in companion documents
>  entitled "Consistent Class and Interface Terminology” and "Local and Nested
>  Static Declarations" have been applied (these are being introduced as part of
>  the Records JEP). In particular, this means that Java SE 16 will support
>  static declarations in two new positions:
>    1. Local, implicitly-static interfaces and enum classes
>    2. Static members of inner classes
>  This requires asserting that local interfaces are not permitted to be
>  `sealed`. (14.3)
> - To enhance narrowing reference conversion to allow for stricter checking of
>  cast conversions with respect to sealed type hierarchies ( 
> - Local classes are not considered when determining implicitly declared
>  permitted direct subclasses of a `sealed` class or `sealed` interface
>  (8.1.6, 9.1.4).
> Comments welcome!
> Gavin

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