Paving the on-ramp

[Brian Goetz]

On 9/29/2022 3:07 AM, Tagir Valeev wrote:
>> ## Unnamed classes
>> ...
>> Such source files can still have fields, methods, and even nested classes, so
>> that as a program evolves from a few statements to needing some ancillary state
>> or helper methods, these can be factored out of the `main` method while still
> I wonder how we tell apart unnamed class syntax and normal class
> syntax. E.g., consider the source file:
>
> // Hello.java
> public class Hello {
>    // tons of logic
> }
>
> void main() {
> }
>
> Will it be considered as a correct Java file, having Hello class as a
> nested class of top-level unnamed class?
> If yes, then, adding a main method after the class declaration, I
> change the class semantics, making it an inner class.
> This looks like action at a distance and may cause confusion. E.g., I
> just wrote a main() method outside of Hello class instead of inside,
> and boom,
> now Hello is not resolvable from other classes, for no apparent reason.

Yes, this is where the bodies are buried.  At some point, the file name 
is likely to come into play, even though we would prefer it not.  (Note 
that we have a little of that issue with "auxilliary classes" today.)   
I think the move here is that for unnamed classes, if there is a "top 
level" nested class that matches the file name, we call that an error.

> I assume that the main() method is required for an unnamed class, and
> if there are only other top-level declarations,
> then it should be a compilation error, right?

Probably so, yes.

>
>> ## Predefined static imports
>> ```
>> void main() {
>>      println("Hello World");
>> }
>> ```
> I wonder how it will play with existing static star imports. We
> already saw problems when updated to Java 9 or Java 14 that
> star-imported class named Module or Record becomes unresolvable. If
> existing code already imports static method named println from
> somewhere, will this code become invalid?

"Star" is the right word.  Currently we have a scheme where single 
imports and beat star imports, so that if someone declares their own 
`println` method, it wins.  Details to be worked out.