RFR: 8305457: Implement java.io.IO [v7]

[Per Minborg]

On Thu, 9 May 2024 18:27:08 GMT, Pavel Rappo <prappo at openjdk.org> wrote:

>> Please review this PR which introduces the `java.io.IO` top-level class and three methods to `java.io.Console` for [Implicitly Declared Classes and Instance Main Methods (Third Preview)].
>> 
>> This PR has been obtained as `git merge --squash` of a now obsolete [draft PR].
>> 
>> [Implicitly Declared Classes and Instance Main Methods (Third Preview)]: https://bugs.openjdk.org/browse/JDK-8323335
>> [draft PR]: https://github.com/openjdk/jdk/pull/18921
>
> Pavel Rappo has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fix System.console().readln(null) in jshell
>   
>   Without it, jshell hangs on me. Will think of a test.

src/java.base/share/classes/java/io/IO.java line 47:

> 45: 
> 46:     private IO() {
> 47:         throw new Error("no instances");

Is this necessary?

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PR Review Comment: https://git.openjdk.org/jdk/pull/19112#discussion_r1596370177