On Mon, 7 Dec 2020 23:47:40 GMT, Mandy Chung <mch...@openjdk.org> wrote:
>> Please review this fix for JDK-8256867. This change no longer throws a
>> ClassFormatError exception when loading a class whose PermittedSubclasses
>> attribute is empty (contains no classes). Instead, the class is treated as
>> a sealed class which cannot be extended nor implemented. This new behavior
>> conforms to the JVM Spec.
>>
>> This change required changing Class.permittedSubclasses() to return an empty
>> array for classes with empty PermittedSubclasses attributes, and to return
>> null for non-sealed classes.
>>
>> This fix was tested with Mach5 tiers 1-2 on Linux, MacOS, and Windows, and
>> tiers 3-5 on Linux x64.
>>
>> Thanks, Harold
>
> src/java.base/share/classes/java/lang/Class.java line 4396:
>
>> 4394: * is unspecified. If this {@code Class} object represents a
>> primitive type,
>> 4395: * {@code void}, an array type, or a class or interface that is
>> not sealed,
>> 4396: * then null is returned.
>
> nit: s/null/`{@code null}`
>
> I'd suggest to clarify if this sealed class or interface has no permitted
> subclass, something like this:
> Returns an array containing {@code Class} objects representing the
> direct subinterfaces or subclasses permitted to extend or
> implement this class or interface if it is sealed. The order of such elements
> is unspecified. The array is empty if this sealed class or interface has no
> permitted subclass.
>
> `@return` needs to be revised as well:
> @return an array of {@code Class} objects of the permitted subclasses of this
> sealed class or interface,
> or {@null} if this class or interface is not sealed
Mandy's suggested wording is good.
I would like to add one more additional point of clarification. It would
be good to strongly connect `isSealed` and `getPermittedClasses` in a
first-class way in normative spec ( similar to isRecord and
getRecordComponents ).
For example,
to `isSealed` add: "getPermittedSubclasses returns a non-null but possibly
empty value for a sealed class."
to `getPermittedSubclasses`: "If this class is not a sealed class, that is
{@link
* #isSealed()} returns {@code false}, then this method returns {@code
null}.
* Conversely, if {@link #isSealed()} returns {@code true}, then this method
* returns a non-null value."
-------------
PR: https://git.openjdk.java.net/jdk/pull/1675
