<html><head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>
<body>
Hi Brian,<br>
<br>
First the intuition and then the rationale.<br>
<br>
Intuition: the extension does not include the period '.' learned
from years of working with existing systems, both shell and
programming languages with file apis.<br>
<br>
Second: In trying to make Path.getExtension() handle all of the use
cases possible, it makes some of them more difficult. In
particular, the cases for removing or replacing the extension are
easier to do with a method for that purpose. It is easier to explain
using a Path.removeExtension() method than to explain how to convert
the path to a string and then remove some number of characters from
the end and recreate the Path. <br>
<br>
Rationale:<br>
<ul>
<li>Other Java libraries that provide path name utilities do not
include the dot as part of the extension; (Guava and Apache
Commons). A mismatch with them (and other common Java libraries)
creates friction and room to make mistakes in conversions
between different representations.</li>
<li>The no-dot representation works just fine except in the case
of trailing dot, which is quite uncommon in practice.<br>
</li>
<li>The APIs provided should do what the programmer needs to do,
not be APIs from which the programmer can create the API they
need and still avoid an explosion of APIs for narrow use cases.<br>
</li>
<li>Extensions are used in many ways, from switch statements to
keys in maps to simple if/then/else; some are hard coded and
others are configured or loaded as plugins. The semantics should
be simple and direct.<br>
</li>
</ul>
For 1) and 3) I would say that both "foo" or "foo." have an empty
("") extension.<br>
Providing a removeExtension() or replaceExtension(String) method can
embed the edge case handling and make the API easy to use without
having to burden the Path.getExtension() method with a model that
includes that complexity.<br>
<br>
Regards, Roger<br>
<br>
<br>
<div class="moz-cite-prefix">On 10/10/23 2:31 PM, Brian Burkhalter
wrote:<br>
</div>
<blockquote type="cite" cite="mid:0B78F716-26F5-43B3-A911-A320ED9B2366@oracle.com">
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
I would like to resurrect this topic which has languished for
quite a while now. It was discussed for probably decades before
my involvement with it. A brief outline of its most recent
history is included below. The essence is that it would be good
to add a java.nio.file.Path.getExtension method, and possibly
one or more companion methods. General comments on the topic are
welcome regardless of whether the included chronology is
reviewed. Things to consider include:</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal; min-height: 17px;" class="">
<br class="">
</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
1) whether a getExtension method ever returns null;</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
2) whether a period character is included as the first character
of the returned extension;</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
3) whether the extension of “foo” (no dot) differs from that of
“foo.” (terminal dot).</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal; min-height: 17px;" class="">
<br class="">
</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
Thanks,</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal; min-height: 17px;" class="">
<br class="">
</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
Brian</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal; min-height: 17px;" class="">
<br class="">
</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
--- snip --- TL;DR --- snip ---</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal; min-height: 17px;" class="">
<br class="">
</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
[1] Feb. 2018</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
Path.hasExtension was initially proposed but dropped in favor of
Path.getExtension. This method was for the most common cases
equivalent to</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal; min-height: 17px;" class="">
<br class="">
</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
Path path = ...;</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
String name = path.getFileName();</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
String extension = name.substring(name.lastIndexOf(“.”) + 1);</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal; min-height: 17px;" class="">
<br class="">
</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
which is to say the extension is the portion of the file name
string after but not including the last period character (dot).
This effort faded out.</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal; min-height: 17px;" class="">
<br class="">
</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
[2] Apr. 2021 - Mar. 2022</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
A pull request was proposed and culminated in the proposal of
the Path method</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal; min-height: 17px;" class="">
<br class="">
</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
String getExtension(String defaultExtension)</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal; min-height: 17px;" class="">
<br class="">
</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
where in the common case the extension is once again the portion
of the file name string after the last dot. For degenerate cases
the “defaultExtension” parameter would be returned. This effort
was superseded by [3].</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal; min-height: 17px;" class="">
<br class="">
</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
[3] Mar. 2022 - Dec. 2022</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal; min-height: 17px;" class="">
<br class="">
</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
This pull request specified the Path method</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal; min-height: 17px;" class="">
<br class="">
</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
String getExtension()</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal; min-height: 17px;" class="">
<br class="">
</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
which in the common case returned the portion of the file name
string after the last dot, and in unusual cases either the empty
string (terminal dot) or null (no dot). For a time this proposal
used Optional but that was dropped as unwieldy. This PR was
approved and integrated.</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal; min-height: 17px;" class="">
<br class="">
</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
[4] Dec. 2022</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal; min-height: 17px;" class="">
<br class="">
</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
Due primarily to the undesirability of the possibility of a null
return value and the lateness of the integration in the
development cycle, the API added in [3] was backed out.</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal; min-height: 17px;" class="">
<br class="">
</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
[5] Dec. 22</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal; min-height: 17px;" class="">
<br class="">
</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
A new issue was filed to track the resumption of eventual work
on this topic. This issue suggested that the last dot be
included in the extension, e.g., the extension of “image.jpg”
would be “.jpg” rather than “jpg” and that the value returned by
getExtension would never be null. It also proposed a
complementary method Path.removeExtension which, together with
Path.getExtension, would form an invariant</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal; min-height: 17px;" class="">
<br class="">
</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
Path path = ...;</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
assert path.equals(path.removeExtension() +
path.getExtension());</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal; min-height: 17px;" class="">
<br class="">
</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
which would obviate the need to handle a period character
explicitly.</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal; min-height: 17px;" class="">
<br class="">
</div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
[1] <a href="https://mail.openjdk.org/pipermail/nio-dev/2018-February/004716.html" class="moz-txt-link-freetext" moz-do-not-send="true">
https://mail.openjdk.org/pipermail/nio-dev/2018-February/004716.html</a></div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
[2] <a href="https://github.com/openjdk/jdk/pull/2319" class="moz-txt-link-freetext" moz-do-not-send="true">https://github.com/openjdk/jdk/pull/2319</a></div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
[3] <a href="https://github.com/openjdk/jdk/pull/8066" class="moz-txt-link-freetext" moz-do-not-send="true">https://github.com/openjdk/jdk/pull/8066</a></div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
[4] <a href="https://github.com/openjdk/jdk/pull/11566" class="moz-txt-link-freetext" moz-do-not-send="true">https://github.com/openjdk/jdk/pull/11566</a></div>
<div style="margin: 0px; font-stretch: normal; font-size: 14px;
line-height: normal;" class="">
[5] <a href="https://bugs.openjdk.org/browse/JDK-8298318" class="moz-txt-link-freetext" moz-do-not-send="true">https://bugs.openjdk.org/browse/JDK-8298318</a></div>
</blockquote>
<br>
</body>
</html>