RFR: 8057113: (fs) Path should have a method to obtain the filename extension [v14]

[Roger Riggs]

On Tue, 26 Jul 2022 00:09:09 GMT, Brian Burkhalter <bpb at openjdk.org> wrote:

>> Resurrection of the proposal to add a method to obtain the filename extension originated in PR [2319](https://github.com/openjdk/jdk/pull/2319).
>
> Brian Burkhalter has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 18 additional commits since the last revision:
> 
>  - 8057113: Revert return type back to a nullable-String; update test
>  - Merge
>  - 8057113: Remove extensions() test method; add threthree new test cases
>  - 8057113: Revert excision of wild cards from imports
>  - 8057113: Add class level apiNote; improve getExtension() specification; remove hasExtension() and replaceExtension()
>  - Merge
>  - 8057113: Change @since annotation to 20
>  - Merge
>  - 8057113: Remove superfluous new Object[] statements from test
>  - 8057113: Fix getExtension() commcents; improve hasExtension() implementation
>  - ... and 8 more: https://git.openjdk.org/jdk/compare/a08870fa...23ca3f10

Changes requested by rriggs (Reviewer).

src/java.base/share/classes/java/nio/file/Path.java line 102:

> 100:  * Otherwise stated, the internal representation might not be recoverable
> 101:  * from the derived path string. This applies to the {@code Path} as a whole
> 102:  * as well as to its components.

This comment doesn't seem specific to the enhancement proposed.
And its a bit vague, if/when included it might benefit from an example or mentioning the character set encoding of file names, if that's the context.

src/java.base/share/classes/java/nio/file/Path.java line 305:

> 303:         } else if (length == 2 &&
> 304:                    !(fileNameString.charAt(0) == '.' ||
> 305:                      fileNameString.charAt(1) != '.')) {

I would have coded it as:

   (length == 2 &&
      fileNameString.charAt(0) != '.' &&
      fileNameString.charat(1) == '.')) {

As a better match for the comment.

test/jdk/java/nio/file/Path/Extensions.java line 64:

> 62:             {".profile.sh",    "sh"},
> 63:             {"..foo",          "foo"},
> 64:             {".....foo",       "foo"},

Duplicates the test  of line 53.

test/jdk/java/nio/file/Path/Extensions.java line 77:

> 75:             {"x.zip",          "zip"},
> 76:             {"y.gzip",         "gzip"},
> 77:             {"z.jar",          "jar"},

Fewer test cases of a file with a 3 or 4 character extension would be fine too. 
Algorithm-wise they are all the same but may give a warm fuzzy that a favorite extension is covered.

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PR: https://git.openjdk.org/jdk/pull/8066