You're making this too complicated.
On their face, startsWith/endsWith(String) are misleading to both code authors and
code readers, and that justifies their deprecation. It will help code authors avoid
making new mistakes. Readers of code that uses these APIs -- even correctly -- can
easily misinterpret the code as if it performed string-based testing and thus be
misled about what the code is actually doing. In both cases, the code is better
replaced with more explicit, if more verbose, alternatives that already exist.
Certainly a file extension API would facilitate use cases that involve file
extensions, such as inspecting a file's extension to determine how to process the
file. I'm in favor of adding such an API. But that's a different topic from this
one, and it should be handled independently.
I did read all of your message but I'm not responding to most of it, because it
doesn't establish a dependency between these two topics.
s'marks
On 1/13/26 12:13 PM, Anthony Vanelverdinghe wrote:
There are 3 questions:
(1) should we deprecate `Path::startsWith(String)`?
(2) should we deprecate `Path::endsWith(String)`?
(3) should we add a file extension API?
And the TL;DR: no, no, yes.
Let's first establish why `startsWith/endsWith` add tangible value:
because `path.startsWith("foo")` is not equivalent to
`path.startsWith(Path.of("foo"))`
and is much more readable than
`path.startsWith(getFileSystem().getPath("foo"))`.
Next, let's consider why people might want to use String-based
`startsWith/endsWith` testing on Path instances:
* testing file extensions = 99.9999% of the times: covered by
`FileSystem::getPathMatcher`
* testing name elements = 0.0000999% of the times: covered by `Path`
* any other use cases = ~0% of the times: covered by
`FileSystem::getPathMatcher`
So it is always possible to do without String conversion.
In fact, it is arguably always a bad idea to do String-based testing,
because `path.toString().endsWith(".java")` will also match a file named
".java",
which on Linux-like OSes would be considered a hidden file named "java" that has
no file extension.
So using a dedicated `PathMatcher` for testing file extensions is more robust and
elegant.
However, when testing file extensions we inevitably start by typing `path.`
(assuming we don't just use a third-party library),
first notice there's no method `getFileExtension` or such,
and then notice `endsWith(String)`
(and maybe we've also noticed `getFileName` and already have
`path.getFileName().`).
At this point it's pure psychology:
we're looking for a method that behaves like String's `endsWith(String)`,
we're looking at a method with the same method signature,
and we can't imagine that the Path class does *not* have a method to test the
filename extension,
so surely this must be it.
And obviously we ignore any hints at the contrary
(like our IDE proposing both `endsWith(Path)` and `endsWith(String)` for
autocompletion).
And we don't bother to read the Javadoc, because in cases like this we can easily
verify our assumptions with JShell
and equally quickly realize our assumptions are wrong.
So yes, this is a common mistake. But this is actually an argument for *not*
deprecating it.
Many developers have bumped into this, but as far as I can tell the mailing list
thread in September was the first in the existence of the API.
And I'm unable to find any previous bug reports either.
And here's why: when we realized our assumptions were wrong, we read the Javadoc,
realized our mistake, learned from it, and moved on.
The Javadoc is crystal-clear, the method overloads another method with the same
behavior, it clearly adds value over the other method.
In other words: we conclude "makes sense" and don't see any reason to complain.
To turn this common mistake into a rare-if-ever mistake, I see two (combinable)
options:
* introduce a file extension API
* replace `startsWith/endsWith` with methods `startsWithNames/endsWithNames`
I don't consider deprecating `startsWith/endsWith` without replacement an option
because:
* these methods add value (as was also argued by Rob Spoor), so it's a net loss
for the Java SE APIs.
And all the people that are happily using these methods today and are unaware of
this mailing list thread will be unpleasantly surprised to see it deprecated
* this means breaking compilation for everyone that builds with "-Werror" and "no
usage of deprecated APIs" is a very common policy.
So people will end up adding a duplicate of the deprecated methods in their own
utility libraries
* this trades one trap for another, much more subtle trap, since people will
blindly replace `"foo"` with `Path.of("foo")`.
(We're having this very discussion because people don't read Javadoc.
So surely we're not expecting people to read the deprecation text and follow the
recommendations, are we?)
Eventually they'll notice there's a bug, add `IO.println(foo)` and
`IO.println(Path.of("foo"))`, notice these both print "foo",
but somehow `foo.endsWith(Path.of("foo"))` results in `false`, eventually find the
culprit ... and then notice the deprecated `endsWith` method did exactly
what they wanted all along
* what would the rationale for the deprecation be? How would you document this in
the Javadoc?
Now you might still say: "People who were looking for a file extension API
regularly ended up here. If you're one of them, use Path::toString instead."
But once a file extension API will be available, it'll be extremely hard to come
up with a reasonable justification for the deprecation.
And as argued above, simple String-based comparisons are rarely, if ever, the most
robust solution
* for `startsWith` in particular: the only argument to deprecate it seems to be
"for the sake of symmetry"
Anthony
On 1/12/2026 8:36 PM, Stuart Marks wrote:
Let's not tie these two issues together.
The discussion clearly shows that the startsWith/endsWith(String) APIs are a trap
that several people have fallen into. On that basis it should be deprecated.
(Ordinarily, so as to emit a warning, and not for removal, so there won't be any
compatibility issue.)
There is also no requirement that a new API be introduced to replace any
deprecated API. As the earlier discussion in the thread shows, both the
path-based and the string-based use cases can be written using existing APIs,
somewhat less conveniently and more verbosely; but these constructs are much more
explicit and so are preferable to the APIs to be deprecated. The deprecation text
should steer people toward the preferred constructs.
It would indeed be nice to have a file extension API, but this has been discussed
several times and has run aground each time for a variety of reasons. Tying these
together will hold up the deprecation for no good reason.
Let's proceed with just the deprecation first and work on the file extension API
separately.
s'marks
On 1/11/26 12:45 PM, David Alayachew wrote:
Thanks for the response Anthony. Messages have been arriving out-of-order for
me, so I didn't see yours at the time of me writing that message.
I think introducing the file extension API first, then gauging the need for a
deprecation before doing it is fine. Sounds like then that we are universally
agreed on the first step being to add the file extension API, yes?
On Sun, Jan 11, 2026 at 2:06 PM Anthony Vanelverdinghe <[email protected]>
wrote:
I dissent. (Apparently my previous message wasn't clear.)
The right order of things is to first introduce a file extension API. Then
see if there's still complaints about `Path::endsWith(String)`. And only
then, if there are, consider taking action.
In my previous message I've already explained how these methods add real,
tangible value and actually are intuitive.
(Again, ask developers to guess how `A::foo(B)` behaves, given that both
`A::foo(A)` and `B::foo(B)` exist, and a large majority of them will
intuitively guess it converts its `b` argument to an instance of `A` and
passes it on to `A::foo(A)`. And their intuition would be correct in the
case of `Path::endsWith(String)`. That being said, I'll be the first to
admit that I've also made the mistake of attempting to use
`Path::endsWith(String)` to test the file extension.)
In hindsight, maybe `endsWithNames(String)` would've been a better choice,
but hindsight is 20/20.
Deprecating these methods now is premature. And deprecating them without
replacement methods would result in way more complaints than there have ever
been about `endsWith(String)`.
Anthony
On 1/11/2026 12:19 AM, David Alayachew wrote:
Of course.
I see lots of approvals and not really any dissenters. Are we waiting for
more responses? Or is there anything we can do to kick start this?
On Fri, Jan 9, 2026, 10:22 PM Brian Burkhalter
<[email protected]> wrote:
Thanks for the corroboration.
On Jan 8, 2026, at 1:50 PM, David Alayachew <[email protected]>
wrote:
Thanks for reviving this.
I am perfectly happy with the idea of deprecating the
Path.{start,ends}With(String), and then only add the file extension
method. Originally, I didn't know that new method was on the table, so
I suggested a rename. But the file extension api feels like the
superior solution.
10 times out of 10, if I am calling endsWith, the only time I am not
looking for "whole" path elements is when I am looking for a file
extension. In every other instance, the api does exactly what I expect
and want. And plus, something like looking for a file extension is
better off being explicit.
