RFR: JDK-8306112 Implementation of JEP 445: Unnamed Classes and Instance Main Methods (Preview) [v8]

[Jim Laskey]

On Fri, 5 May 2023 09:43:04 GMT, Jaikiran Pai <jpai at openjdk.org> wrote:

>> Jim Laskey has updated the pull request incrementally with two additional commits since the last revision:
>> 
>>  - Anonymous main classes renamed to unnamed classes
>>  - Add test
>
> src/java.base/share/classes/jdk/internal/misc/MainMethodFinder.java line 70:
> 
>> 68:                         correctArgs(method) &&
>> 69:                         // Only statics in the declaring class
>> 70:                         (!isStatic(method) || declc == refc)
> 
> Should this also exclude `abstract` and `native` methods named `main`?

abstract would be overshadowed by its implementation and native is fair game.

> src/java.base/share/classes/jdk/internal/misc/MainMethodFinder.java line 134:
> 
>> 132: 
>> 133:     /**
>> 134:      * {@return priority main method or null if none found}
> 
> I think this javadoc is perhaps outdated? The current implementation of this method throws a `NoSuchMethodException` when it can't find any eligible main method.

Changing

> src/java.base/share/classes/jdk/internal/misc/MainMethodFinder.java line 152:
> 
>> 150: 
>> 151:             List<Method> mains = new ArrayList<>();
>> 152:             gatherMains(mainClass, mainClass, mains);
> 
> The `try` block above is there to find `public static void main(String[])` in the launched class. When it's not found, then we gather the potential main methods (as listed in the JEP). The implementation of `gatherMains(...)`, in its current form starts gathering the main methods from `refc.getSuperclass()`, where `refc` in this case is the `mainClass`, which is the launched class.
> 
> So if I'm reading this correctly, then I think it's going to completely skip the launched class for looking any potential main methods and instead start looking for them in the launched class' super hierarchy.

It doesn't skip, it just adds the super members first. However, I should move the `gatherMains` to the end since the sort pushes the best candidate to the top  and (was originally taking the last one with an opposite sort order). The sort order is

- static trumps non-static
- public trumps protected/package-protected
- arguments trumps no arguments
- depth in hierarchy

Let's say we have a hierarchy of `B` inherits from `A`.  If `B` contains `public void main()` and `A` contains `public void main(String... args)`,  `A`'s `main` trumps `B` `main` since it has  arguments.

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PR Review Comment: https://git.openjdk.org/jdk/pull/13689#discussion_r1186247702
PR Review Comment: https://git.openjdk.org/jdk/pull/13689#discussion_r1186249703
PR Review Comment: https://git.openjdk.org/jdk/pull/13689#discussion_r1186245072