Paving the on-ramp

[Brian Goetz]

This question came up in a few different forms, but there's a reason why 
I've only relaxed the "must be public" for classes in the unnamed 
package: security.

There may be existing classes with a package-private instance main() 
method, and they may have reasonably assumed that these are only 
callable from within the package.  If the launcher can barge in and open 
non-public classes and call non-public methods, that may be surprising.  
Restricting the "main can be non public" to the unnamed package is 
justifiable because we can reasonably treat the launcher as being part 
of the unnamed package (and therefore this rule falls out from ordinary 
access control) and because it is disadvised to distribute libraries 
that use the unnamed package, reserving it instead for local 
experimentation.

Framing the launcher as "just some Java code in the unnamed package" 
also demystifies the launcher a bit.

On 9/28/2022 3:49 PM, Kevin Bourrillion wrote:
>
>      - Relax the requirement that the class, and `main` method, be
>     public. Public
>        accessibility is only relevant when access crosses packages;
>     simple programs
>        live in the unnamed package, so cannot be accessed from any
>     other package
>        anyway.  For a program whose main class is in the unnamed
>     package, we can
>        drop the requirement that the class or its `main` method be public,
>        effectively treating the `java` launcher as if it too resided
>     in the unnamed
>        package.
>
>
> Alternative: drop the requirement altogether. Most main methods have 
> no desire to make themselves publicly callable as 
> `TheClass.main(args)`, but today they are forced to expose that API 
> anyway. I feel like it would still be conceptually clean to say that 
> `public` is really about whether other *code* can access it, not 
> whether a VM can get to it at all.
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