RFR: 8357016: Candidate main methods not computed properly

[Jaikiran Pai]

On Thu, 15 May 2025 16:42:48 GMT, Jan Lahoda <jlahoda at openjdk.org> wrote:

> A consider class like this:
> 
> 
> public class TwoMains {
>     private static void main(String... args) {}
>     static void main() {
>         System.out.println("Should be called, but is not.");
>     }
> }
> 
> 
> The `MethodFinder` will do lookup for the `main(String[])` method, and it finds one, so does not proceed with a lookup for `main()`. But then, it will check the access modifier, and will reject that method, never going back to the `main()` method. This is not what the JLS says about the lookup - the private method is not a candidate, and should be ignored.
> 
> Something similar happens if the return type is not `void`.
> 
> This PR is fixing that by checking whether the `main(String[])` method is usable early, and falling back to `main()` if it `main(String[])` is not usable.
> 
> It also removes the check for the `abstract` method, as that, by itself, is not really backed by JLS, but adds a check for `abstract` class, producing a user-friendly message is trying to invoke an instance `main` method on an `abstract` class (which, obviously, cannot be instantiated).

src/java.base/share/classes/sun/launcher/resources/launcher.properties line 283:

> 281:     make inner class static or move inner class out to separate source file
> 282: java.launcher.cls.error8=\
> 283:     Error: abstract class {0} can not instantiated\n\

Nit - should this use a comma instead of the newline?

src/jdk.compiler/share/classes/com/sun/tools/javac/resources/launcher.properties line 113:

> 111: # 0: string
> 112: launcher.err.cant.find.main.method=\
> 113:     can''t find main(String[]) or main() method in class: {0}

Out of curiosity, why the double single quotes? I see it being used in other messages in this file as well, so it doesn't seem to be a typo.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25256#discussion_r2092763055
PR Review Comment: https://git.openjdk.org/jdk/pull/25256#discussion_r2092765139