RFR: 8302603: Use Set.of in java.nio.charset.Charset [v3]

[Glavo]

On Mon, 20 Feb 2023 18:01:13 GMT, Alan Bateman <alanb at openjdk.org> wrote:

> > I have updated the code.
> 
> Thanks for the update. I think it looks okay although "as" looks a bit strange here, I think I would use aliasSet or something better.

Well, the name `as` is a bit strange. I didn't use the name `aliasSet` because I didn't want to shadow the field. 

Now I simply name it `set`. I think this name is clear enough in this context.

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PR: https://git.openjdk.org/jdk/pull/12570