RFR: JDK-8283594: Improve docs of ElementScanner classes [v3]

[Joe Darcy]

On Thu, 24 Mar 2022 00:24:36 GMT, Jonathan Gibbons <jjg at openjdk.org> wrote:

> In the implementation, it looks like the `visitXYZ` methods call the `scan(Iterable<? extends Element>, P p)` methods.
> 
> However, it is notable that the `Iterable` overload is `final`, (along with the 3rd overload that defaults the `P` parameter), thus effectively guaranteeing that the `scan` method that takes a single `Element` will indeed be called.

Right; calling "scan(Element, P)" as an implementation detail happens by using a call to the final scan method accepting an iterable.

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PR: https://git.openjdk.java.net/jdk/pull/7932