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.
