RFR: 8298318: (fs) APIs for handling filename extensions

[Brian Burkhalter]

On Tue, 17 Oct 2023 19:52:14 GMT, Brian Burkhalter <bpb at openjdk.org> wrote:

> Add to `java.nio.file.Path` a method `getExtension` to retrieve the `Path`'s extension, and companion methods `removeExtension` and `addExtension`.

This request follows from previous work outlined in this [nio-dev thread](https://mail.openjdk.org/pipermail/nio-dev/2023-October/015084.html).

For a given `Path` `p`, the following invariant obtains:

assert p.equals(p.removeExtension().addExtension(p.getExtension()));

Replacing an extension may be accomplished by composing the removal and addition methods as:

jshell> Path losslessImage = Path.of("photo.png");
losslessImage ==> photo.png

jshell> Path lossyImage = losslessImage.removeExtension().addExtension("jpg");
lossyImage ==> photo.jpg

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PR Comment: https://git.openjdk.org/jdk/pull/16226#issuecomment-1767071295