[External] : Re: Can we deprecate Path.endsWith(String)?

Wed Jan 14 18:20:19 UTC 2026

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 <anthonyv.be at outlook.com> 
>>> 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
>>>>     <brian.burkhalter at oracle.com> wrote:
>>>>
>>>>         Thanks for the corroboration.
>>>>
>>>>>         On Jan 8, 2026, at 1:50 PM, David Alayachew <davidalayachew at gmail.com>
>>>>>         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.
>>>>
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