> The model was powerful, but also mentally heavy
No it isn't! it is this interpretation that kills off the null-safety debate entirely. Saying you have a variable that cannot be null is not a mentally taxing distinction, especially since everything is labelled thoroughly.
> The team, faithful to the lesson “simplify the model for the user, even at the cost of the performance ceiling,” ultimately dismantled this dualism.
but it would have simplified it for the user.
The whole attitude and process around this and the other topics gives me very little faith that Java can be steered in a sensible direction here. The type system of a programming language is supposed to give convenient guarantees to the developer on a CPU that can only do numbers. There is no reason to reduce the optional(!) safety guarantees you can offer with the excuse of "too mentally taxing".
Hell, they even get there half way by recognising:
> the language model and the JVM model don’t have to overlap one hundred percent
I agree. The stewardship of Java seems rather lacking - particularly when compared to that of .net, where MS etc. mostly seemed to make the correct decisions from the start.
Does Java even have any value or mindshare at Oracle nowadays? The company seems to be a datacentre/compute business at this point, with appendiges for its legacy activities and a vast overhang of debt.
I sometimes wonder if the only parts of Oracle that are still profitable are the Legal and Lawnmower divisions.
Now, as a member of the Java team (although I'm not directly involved in Valhalla), I'm obviously biased so let me just say that both designers and fans of programming language features would do well to remember two things:
1. Opinions about features are almost never universal, even among experts, and almost each of them is about a tradeoff where different people prefer different sides. It is rare that some scientific study settles the issue.
2. These preferences are often not evenly split. Even when both sides are equally confident that their preference is the right one, sometimes 80% or 90% of programmers share a preference. The people with the strongest opinions are more often than not in the minority, because most programmers don't think so much about the programming language (nor, I would say, should they).
All of the language differences between .NET and Java fall in this "non-consensus" zone, and at least in one area I was deeply involved with, virtual thread, I can say that we thought that whatever we do we mustn't do what .NET did and that what they chose didn't work out well for them at all.
These people may point out that languages become more or less successful not because of the things these people care about but because of other factors. And they're right, but then the question is, shouldn't a smart product team focus more on the things that actually matter more to more people?
Programming languages are tools, and so their value is not intrinsic, but comes from the value of the software they're used to create. Now, some people claim that Java's success is largely the result of it being one of the most hyped languages of the late 90s and early 00s, alongside VB, Delphi, FoxPro, and C#. But this claim doesn't stand up to even the slightest scrutiny.
"All differences are opinions....except what .net did. Those are wrong!"
I personally think Java continues to to waste a lot of time and come to a slightly more verbose and worse solution again and again.
Structured concurrency is like c# async/await with less sugar. Streams are just LINQ but worse.
It's probably exactly because of the "not like .NET! We must be different to explain being late" mentality.
They have different philosophies though, C# is mostly "give the developer a complex toolkit so they can do whatever they want, but keep the runtime simple", while Java is more like "keep the language as simple as possible, and put new features mostly into the runtime making it more complex, but benefiting even old code".
Async vs virtual threads is a clear example of that. The former makes the language much more complex, and has a huge surface area where it may clash with other features, so a developer has to remember all of these. But it's a simple machinery under the hood.
Meanwhile virtual threads don't change the language at all, it's the same as it was with Threads, but under the hood it is a very complex feature.
And in this particular instance I think it is quite clear cut that Java made the correct decision, for the most common use case of these languages having non-blocking IO "automatically" makes for significantly better user experience.
For things like UI programming where you need a main thread or where you do need a cross language OS thread, I think Java is going to end up more complex. Under the hood it is very complex and that _will_ show itself.
So from my perspective it's not virtual threads, it's virtual threads with structured concurrency vs async/await. When you look at it that way, the comparison of complexity is certainly not seamless or simple.
But that doesn't mean the preferences are equally distributed. Some people liked Betamax's better picture quality while others liked VHS's better recording times, but they didn't do it in equal numbers. And that's what's funny, because there are two languages doing as well as Java or better (one of them is much more popular), and yet what's almost universal is that when people say "Java is worse than X", X is invariably a language that's doing much worse than Java.
I'm not saying that there isn't much to learn from less popular languages, but the claim "Java is consistently making the wrong decisions compared X" doesn't make sense when X is consistently losing to Java.
And I can even give you the secret to our strategy: Make Java the language that people who choose it regret less than people who choose other languages.
It felt like magic, maybe too much magic, but so useful nevertheless.
As to value types and null, I'm not sure about the current picture, but the general idea is that you declare what semantic properties you want - identity or not, nullable or not, tearable or not - and then the compiler picks the best technical in-memory representation for each use. For example, the compiler could choose not to flatten variables that could be null in the heap but to flatten them in the stack. That's the general idea, but I'm not sure about the details, some of which may yet change.
More generally than just Java, nullability is often a property not of a type but of a variable. For example, in C, an int may not be null, but a pointer to an int may be. Now, in C, `int` and `int*` are two different types, but that's exactly a distinction that the original projection-spit design made and we wanted to avoid. But you could still end up with a variable that could hold either an integer or a null and another that may hold an integer but not a null, only this is separate from the reference/value projection, which combines both identity and nullability (in C, `int*` is not only nullable, but also has identity).
I'm going to hard disagree here. And the syntax proposed in the Null-Restricted Value Class Types JEP is a major step backwards.
I want to banish nulls from my codebase, completely. I can currently do this with a variety of annotations (at the package-info.java level) and tooling, though it's not integrated well with the language.
Forcing exclamation marks into every variable and parameter is a lot of annoying noise that quite simply nobody will do. The default should be non-nullable, especially for value types.
Declaring whole types as non-nullable is less noisy and errorprone than annotating every variable declaration. If you aren't going to give me "declare the whole codebase as non-nullable" then at least give me something coarse-grained.
Then you didn't read the JEP draft (it's not an accepted JEP) carefully. It says, under "future work":
Providing a mechanism in the language to assert that all types in a certain context are implicitly null-restricted, without requiring the programmer to use explicit ! symbols.
In other words, the draft already incorporates your point, but JEPs (both drafts and actual JEPs) follow the pattern we've found to work so well, that features are best delivered piecemeal rather than in a big bang.
Having said that, I don't know the current plans for this matter, as that document is only in Draft status, so saying it's good or bad is pointless, as it's not even a proposal yet, just something being explored.
I don't think this syntax is desirable as currently proposed, and that one line under "future work" is doing far too much lifting. My sincere hope is that there are people closer to the process that also feel this way, they will provide similar feedback, and the next draft will be something completely different.
So consider that draft as an idea for how the site-specific nullability annotations could work rather than an idea for how nullability could work in the language in general.
That's fine but it's still a bad choice. The problem is that it defaults to everything nullable and adds noise for non-nullable. This is backwards; in the overwhelming majority of software that people use Java for, non-null is the common case and nullability is the exception.
Kotlin and Typescript got this right. Nobody wants! to! write code! like! this! And they won't, so the feature won't get used and we're back to everything being nullable.
Except there's no choice here. It's a draft of an exploration of a portion of a feature.
Drafts are ideas that have not even been submitted for consideration for inclusion in the roadmap. You can find drafts over ten years old that have long since been superseded by other ones or abandoned altogether: https://openjdk.org/jeps/0#Draft-JEPs. Some JDK engineers write JEP drafts when they feel they get close to something they would like to propose, while others write drafts for pretty much any idea they have.
> The problem is that it defaults to everything nullable and adds noise for non-nullable
It doesn't, though. Even if this draft ever becomes a JEP (and I don't know if it or anything like it will), in its present form or another, it would still, like most JEPs, describe only part of the feature. It's perfectly on point for one JEP to describe the explicit nullability annotations, while another describes the defaults. Smaller features than this have been split into two or three JEPs. This is just how Java features have been described and delivered for years now (see how many JEPs patterns were split into: https://openjdk.org/jeps/0).
It's perfectly okay to dislike some design, but I find it strange to assume, based on a draft of a portion of a feature that one of the most experienced and successful programming language design teams in the history of software is likely to get it wrong. Maybe wait until there's an actual proposal and a roadmap for the complete feature before critiquing it? It's like seeing a draft of some building's foundations by a prestigious architectural firm and saying, these idiots forgot to plan a roof.
I'm not saying that the people who wrote this are dumb, or that Java is a bad language, or that it's time to move to Kotlin, etc. I use Java every day. I pick Java for greenfield projects. I'm on Team Java.
I'm saying I don't like this proposal. I happily accept that this proposal might not become part of the Java language. That's great! I'm spending time writing this in public specifically to discourage it in some tiny way.
It would be fair to tell me "you should write this to the proposal writers directly". And I understand how the language snobbery on HN might make you feel defensive - I often feel that too. But I think my criticism here is valid.
And I'm trying to tell you that this document is not what you think it is. It's a rough sketch of a building's foundations and your critique is about the roof. Even if this were to become a proposal, it's likely the matter of defaults of this feature will be covered by a different JEP, because Java features are usually broken down into multiple JEPs. What you're complaining about may be part of the feature, but it is not covered by this document. If this becomes a JEP and another JEP talks about nullabilty defaults, then you could criticise the selection of defaults, but that particular aspect of this feature is outside the scope of this particular document. So one, this is not a proposal, and two, you haven't seen the description of the part of the feature you want to criticise.
We are well aware that splitting features over multiple JEPs can invite such misunderstandings, but that doesn't change the fact that Java features are, at least currently, split over multiple JEPs. We are also well aware that if this does become a proposal, adding ! everywhere is not what we want, but we want to cover that aspect in a different document, as we usually do. Most Java users aren't confused by this because they don't read the JEPs at all, but such splits help focus the discussion on one aspect of a feature at a time. So your desire for a non-nullable default is very understandable, it's just not relevant as a critique of this document.
For example, the virtual threads JEP described a pinning limitation. We knew it reduced the applicability of that JEP and said as much. We just wanted to address it in a different JEP, and so we did (https://openjdk.org/jeps/491). Ever since the JDK switched to time-boxed, semiannual releases, this is how we've delivered features: in multiple pieces. The same applies to Valhalla.
This is a tangent, but I'm not sure I follow this. Can you give an example to make this clear?
In Java, you can ask, `x instanceof T` (and this is a runtime test), which means, is x one of the values in the set of values allowed by T. `null instanceof Integer` is false, even though a variable of type `Integer` can be assigned a null. So you can think of `Integer x` as being `Integer|null x`, i.e. x can hold a null, even though `null instancof Integer` is false.
type Foo = { x: number; }
type Bar = { x: number; y: number }
type FooBar = Foo | Bar;
function baz(x: FooBar) {
if ('y' in x) {
// compiler now knows x is a Bar
}
}
What was taken away is the other, identity-having functionality of Integer and similar (e.g. no synchronization).
Curious if you think fibers vs async/await is still in this zone (amongst experts). It seems fibers are objectively better. But I'm no expert*
The property lookup and modification process in JS is complex enough as is, is not specified in an atomic kind of way, and has many opportunities for user code to be run as part of accessor properties. Enabling it in multithreaded implementations is tricky without opening up deadlocks when modifying property collections, and even with that could likely be broken by some suitably evil code. Ive worked on more than one implementation that offered some degree of multithreaded access and it’s generally only safe when limited to simple properties.
Async / await avoids those issues because none of the places where user code can be executed allow async code, so there is no opportunity for the world to be changed under your feet during something like property access.
Structs, Shared Structs, and Synchronization Primitives
There are a few things that would be required to make it all work, this would be one of them.
An alternative solution to that of fibers to concurrency's simplicity vs. performance issue is known as async/await, and has been adopted by C# and Node.js, and will likely be adopted by standard JavaScript. Continuations and fibers dominate async/await in the sense that async/await is easily implemented with continuations (in fact, it can be implemented with a weak form of delimited continuations known as stackless continuations, that don't capture an entire call-stack but only the local context of a single subroutine), but not vice-versa.
While implementing async/await is easier than full-blown continuations and fibers, that solution falls far too short of addressing the problem. While async/await makes code simpler and gives it the appearance of normal, sequential code, like asynchronous code it still requires significant changes to existing code, explicit support in libraries, and does not interoperate well with synchronous code. In other words, it does not solve what's known as the "colored function" problem.
Structure concurrency/virtual threads seem like a good fit for Swing; just have your event handler fire off virtual thread[s] and do your work and call SwingUtilities.invokeLater to schedule the result to be applied on the event loop thread when you're done. Structured concurrency simplifies managing groups of concurrent tasks, cancelation, etc.
You still can't block in UI code, right? You don't know whether you're on a virtual thread or the UI thread (even if its virtual) by design. You still have to bifurcate your APIs into blocking and non-blocking, don't you? Virtual threads will help you keeping the CPU fed but it won't handle separating UI and non-UI work, or know when a frame deadline ends.
Have there been Swing specific updates to deal with that?
This is true in some languages but not in Java. The limitations (and performance cost) are not from the nature of continuations/stackful coroutines/"colourless functions", but from their interaction with other constraints and existing designs in the language. E.g. in Java, virtual threads have zero impact on FFI.
In general, the costs and limitations associated with a feature in language X don't extrapolate to language Y, because they often stem from interaction with existing constraints in language X.
The design of FFI is a very common source of problems for various features. For example, if the FFI is designed such that you frequently pass pointers to to objects to C, that can have a big impact on other features. In Java, you nearly always only pass pointers to "off heap" memory, i.e. memory that's not managed directly by the JVM. While this has no performance cost, you could say that this, in itself, has some convenience cost, except Java programs need to rely on FFI much less than other languages, so the overall cost to convenience is low.
But 1. there's no speed penalty in Java for doing that, and 2. In Java, calling native functions that block (which is the only time this limitation matters) is rare, especially in high concurrency situations where you'd use virtual threads in the first place.
I was at a conference on scientific programming in Java very early on that Geoff Fox put on up at Syracuse and we had a list of requests from Sun that they didn't give us but Microsoft gave many of them right away.
On the other hand I really like Java's all-virtual approach to inheritance because the .NET model gives programmers more ways to screw up and get confused.
Both languages slipped in generics after 1.0. Java used type erasure in a way that made it so a List<String> is really a List so generics could be retrofitted easily to existing code. .NET's implementation of generics let you do more but caused a rift in the ecosystem between generic and non-generic collections.
I'd say long term Oracle's stewardship of Java has been very good. JDK 8 puts lambdas on your fingertips with a very fluent syntax that belies the idea that Java is terribly verbose. Since then Java has gotten steadily better release after release while maintaining great compatibility.
I work with people who are conservative about updates because they are worried about breaking things but for the last few LTS releases I've said "it ought to be really easy, let's give it a try" and it is really easy and we get performance improvements we can feel.
Thing was a lot of Microsoft APIs for GUIs and whatnot used the List and if you wanted to use the List<X> you had to copy the list or make a wrapper or something. You might say, "just use the List" but at that point (circa 2008) I had to also use the List<X> for some API so I always had to do some conversion.
Then, when WinForms or WPF wanted a list, you could just give it a List<T> instance, and it would talk to it via IList, boxing and unboxing if necessary.
What you describe happened in the other direction - if you had, say, a generic method operating on IEnumerable<T> or IList<T>, and wanted to pass it a WinForms collection. WinForms generally defined strongly typed collection classes on a case by case basis, but none of them implemented the new interfaces. It was there where you had to wrap things, most often using AsEnumerable<T>().
In what way? If anything Java's main developers (employed by Oracle for the most part, working on the completely open source and free OpenJDK) are extremely knowledgeable and are responsible a big jump in how fast the platform evolves. They have added proper algebraic data types to the language, delivered virtual threads and garbage collectors that decouple pause times from heap size. Like if anything, Java is at the best place it has ever been.
No they haven't. E.g. they added a class that superficially looks like Option but subtly breaks the rules that Option is meant to follow, ensuring that no-one can ever manage to migrate existing codebases away from using `null`.
The stdlib's Option type predates this language update by a long shot, so it doesn't use sealed classes, but it is now possible to have the usual FP "Maybe" type in Java:
``` sealed class Maybe<T> permits Some, None { record Some<T>(T obj) {} record None() {} } ```
(You will probably have to write Maybe.Some and I might have messed up the generic syntax as I wrote it on my phone, but that's mostly how it looks)
The main difference is that (T | Null) | Null = T | Null, while Maybe<Maybe<T>> is different from Maybe<T>
First, a record can't extend anything, it's not even valid syntax, so a sealed class can't permit record subclasses. So no, it's not possible to create a Maybe<T> class in Java that can only represent a Some<T> or a None<T> record. You could do it with regular classes, or if it's ok for Maybe<T> to be an interface.
Secondly, regardless of the sealing, nothing in any current or near future of Java prevents you from assigning `null` to any class of any kind you might create. So you can always have `Maybe<T> x = null`, or even `Some<T> x = null`.
None of this will change with the adoption of value classes either. So no, there is absolutely no way in Java to create a real Optional/Maybe type that would guarantee that a variable is either an object of a given type or None. There is probably some way to do it for your specific project using annotation processors, of course, but that is very different from having built-in support.
> So you can always have `Maybe<T> x = null`, or even `Some<T> x = null`.
Yeah and? Practically every type system have escape hatches, like Haskell can also do side effects without the IO monad, does it make the latter useless?
This also has significant impact for serialization/de serialization - a classic place where you get unexpected nulls, that Java Optional/Maybe don't help with at all.
Types are both for the compiler, as well as for the developer. Maybe types are implicit documentation telling the developer that it is meaningful in the application that this field can have a None state.
That's a huge code smell to ever set null to an Optional/Maybe and code reviews, linters, nullness analyzers all should/will flag such.
Like I have never ever had an NPE from an Optional being null. Sure, complete null safety would be better of course, but in this very instance it ain't buying you much.
Use a regular class to signal that you may or may not have a value.
Wrap it in an optional to signal that you may or may not have a value.
See the problem?
Well wasn't that the argument above, that the stuff they added so far isn't proper at least in part because they didn't fix that problem yet?
And a promise to eventually fix a busted implementation doesn't undo it being busted for a significant amount of time.
It is all about having AI on the framework, Aspire, multiple Web and Desktop frameworks all over the landscape.
Those interceptors and inline arrays via attributes instead of proper language grammar aren't that great either.
Yeah. Even when they add new grammar nowadays, it's always just something that trivially sugars away into previous grammar (see: records, `with` clones, extension properties, required, etc).
The moment they need something that it's slightly more complex... Out of scope. Even when it's completely necessary for the thing to be useful in practice.
For example, they added `required`, `record`s and property initializers, giving us good reasons to write `new Foo { A = a, B = b }` instead of `new Foo(a, b)`. A and B must be positive, so you'd write:
public required int A { get; init => field = value > 0 ? value : throw ... ; }
public required int B { get; init => field = value > 0 ? value : throw ... ; }
But then the requirements change: A and B must be positive, or they must both be zero at the same time.
This cannot be expressed at all with initializers. You simply cannot add code that runs after all initializers are called. You're stuck chasing every single initialization of Foo and using a constructor or factory method instead. Shipped it as a public API? Too bad. Should have seen it coming!
The new features are filled with this sort of thing. As if Microsoft never used them beyond the most basic examples. Or maybe they did, and explicitly chose not to fix it and solve later.
The reality, and I can see this on my bubble, is that the .NET shops are mostly former Microsoft shops now saving Windows licenses by deploying on Linux.
Stuff like MAUI remains pretty much constrained to former Xamarin customers.
Thus minimal APIs, aspire, Blazor, and whatever comes up to support those use cases first.
There are some podcast interviews from David Fowler and Maddy Montaquila where they touch the adoption issue among newer generations.
Wut? I did worked on .net projects and all it achieved was making me like java a lot more then previously.
To me it felt a bit less like a religion and more like a language. It didn't force me to do things a particular way, quite as much. (Still more than I would have liked, though! After all, it's called that[0] for a reason :)
[0] https://www.reddit.com/r/ProgrammerHumor/comments/ddc4b0/mic...
-Java always has an API, .NET is about extending an existing application (Servlet API vs IIS)
-Java has a nicer IO as .NET has bidirectional streams (You can't wrap streams in .NET).
-Linq is nice but has a huge caveat: if a Linq provider does not implement it fully to falls back to the .NET collections. So trying to 'Skip' and 'Take' on a ActiveDirectory will fall back to collections in memory and cause a crash on a huge AD in production (Yes had the pleasure).
-Java's Eco-system is way bigger.How do you expect this to work then? If the provider is bad, blaming LINQ for it makes no sense...
You either have a high level of abstraction and possible performance pitfalls - or a low level of abstraction, and also performance pitfalls since the code is less modular, more coupled and harder to read.
LINQ can in many cases improve performance significantly in large applications when used properly, since it avoids N+1 query problems due to implementation hiding/modularity, and allows composing parts of queries across different vertical subsystems of the application (vs. each subsystem doing its own query and then joining them with more boilerplate).
Nothing in Java compares to this. jOOQ and Hibernate (and the rest in the ORM ecosystem) are pale shadows, exactly due to lacking language features (such as reified expression trees), and even then, they only work with databases.
Yes Java does not have an alternative for Linq and jooq is a poor knock-off compared to this but then again: I do not care much for JPA/Hibernate.
I don't think this is true anymore since ASP.NET Core. While you can still run under IIS but it's a more typical reverse proxy setup instead of running inside IIS.
> You can't wrap streams in .NET
You've always been able to wrap streams in .NET so I'm not sure what you mean by this
If we want to compress a file we normally just wrap the file ouputstream in a GZIPOutputStream so we add features by wrapping it.
Second, working in C# felt clunky, as if every other thing was done to check the checkbox "done" and the author called it the day once it sorta kinda worked. There was some additional syntactic sugar in that language that was nice, but it did not made that much difference in practice and I don't miss it after coming back to java.
Third, I found the obsession with bashing java by people who have no idea how java projects look like and which problems they have annoying.
Part of the reason for that is that Java is older. https://en.wikipedia.org/wiki/C_Sharp_(programming_language)...:
“In interviews and technical papers, he has stated that flaws in most major programming languages (e.g. C++, Java, Delphi, and Smalltalk) drove the fundamentals of the Common Language Runtime (CLR), which, in turn, drove the design of the C# language.”
Also, some of Java’s design warts may be there because Java was initially envisioned for much smaller devices.
That is an eloquent way of re-writing the history of Microsoft stealing Java and not being allowed to get away with it.
This cracked me up
I think (but may be wrong) their concerns are about the insert part. C# always had structs, Java wants to add them in a backward-compatible way. They want, for example, existing generic container classes pulled in from a .jar (i.e. already compiled) to support Java value types.
As for structs, Java avoids e.g. tearing issues with making them immutable, while it is easy to optimize it to local modification under the hood.
All the types that are value types in semantics, e.g. Optional, should be proper value types on Valhalla.
Additionally, they should be compatible with existing code that expects them as parameters, fields,.... without being recompiled from source.
If it is a complete new type without backwards compatibility, no one is going to adopt it, other than a few niche cases.
And as proven in the recent announcement, they had to rewrite parcel from C++ into Go, as they didn't found a comparable library in Go ecosystem.
There is also another interview, where again they mention having used AI as tool for code rewriting as well.
Also to note that it was pointed out that Native AOT wasn't up to the job, again something that both Java and C# failed not having done it properly from day one.
> Also to note that it was pointed out that Native AOT wasn't up to the job, again something that both Java and C# failed not having done it properly from day one.
It's been working fine for a few years now. The only problem I know is there is little to no reflection allowed (by design) so a lot of code out there is not compatible with it yet. Not sure if that's what turned the TypeScript team away from it.
https://youtu.be/UJfF3-13aFo?t=1453
As for the AOT part, one would expect that being all Microsoft, they could work together to fix whatever were the issues with Native AOT.
Second mover advantage.
Java is more used than C#, they can wait before delivering a new feature (given their leader position) but cannot deliver a flawed implementation that would stay in the language forever. Glad to have virtual threads and the backward compatibility that comes with it instead a Async version of sync methods + async and await keywords all over the code and Task as a return type in my interfaces methods to allow implementations to do non blocking I/O calls if they need.
I use Java and C# and appreciate them both.
and then they make everything nullable by default in c#...
But a huge mistake (IMHO) was not having nullability part of the type system. You can still do this with type erasure.
Anyway, I read your comment as "nullability isn't complex" (paraphrased) but that's not the author's point. What's complex is having a value class and a regular class of every class and you don't necessary know which one you're dealing with at the language level.
C++ is a great example of this. You can create an object ont he stack or the heap and that's really what we're talking about with that proposal. And that's a nightmare. Combined with pointers it meant you never knew if you could free something or not and that ownership had to be passed around with vague comments like "// retains ownership".
Anyway, the whole article is a great tale of how difficult it is to retrofit things later and how difficult it can be to fix mistakes later (eg java.util.Date).
This is often given as the defensible reason, but it's not even that true. Java 1.5/5 had several "breaking" changes in it regardless including the newly reserved 'enum' and a whole freaking memory model update.
And besides if any of your dependencies updated for all practical purposes you did, too, since you had to use a newer runtime to run their code regardless, it never really made sense to keep using an older javac out of spite
Now, one can argue that this is just smoke and mirrors with type erasure and it is but you can already put a Date into a List<Point> if you're so inclined because the JVM doesn't know the difference, hence type erasure. So this is no different.
I'm no JVM expert but from reading the article it seems like the chosen solution for value classes is to treat them all as a single L-type in the JVM where each primitive type is its own L-type. If I read the correctly, it means that if you have a Point value class then on the JVM level you'll be able to stuff any value class into there if you're so incline, just like with List<Point>.
Obviously we need to be concerned with fuzzing (moreso in C++) but here really we're just trying to have sensible defaults that aren't guaranteed because we can't design the language how we want from the ground up without making a new language.
Oh and there is a prosopal for this [2]. Personally, I prefer the Hack version.
And that's a massive problem that they're planing to solve with specialized generics.
> If I read the correctly, it means that if you have a Point value class then on the JVM level you'll be able to stuff any value class into there if you're so incline, just like with List<Point>.
I'm not sure what you mean. An L-type is an object reference. E.g. Ljava/lang/String, Lcom/org/CustomObject. The issue you're conflating is the erasure of List<T> to List<Object> and it's L-type Ljava/util/List.
> I prefer the Hack version
Hack/HHVM didn't have to worry about backwards compatibility.
---
The blog post does a pretty high level overview of the implementation, but my understanding of it is the following:
1. They are adding a new bytecode class flag for value classes. Bytecode descriptor for value classes are exactly the same (L-type).
2. Primitive wrapper classes will become value classes.
The difference from the CLR is that the JVM implementation is backward compatible with linked legacy bytecode. As they can accept a value class instance into their methods due to the same L-type. It's just additional metadata added to allow the JVM to stack allocate the class.
---
Separately, to handle generics:
1. Parameterized container classes will be flagged with a new bytecode to enable parametric attributes on initialization with the additional data of the parameters in the Constant Pool. Bytecode descriptor for classes are exactly the same with type-erasure, e.g. List<SomeType> erased to Ljava/util/List.
2. Initialization of parameterized classes are done with the additional metadata of the type argument stored in the Constant Pool.
3. The runtime does monomorphization of the parameterized class.
It doesn't seem too different to what the CLR does, i.e. runtime monomorphization. The difference is the JVM implementation is backward compatible with older type-erased code, i.e. the restrictions in Java due to type-erasure are exactly the same as before and the L-types don't change. It's just additional metadata added to allow the JVM to monomorphize the classes for performance.
---
In summary, value objects and specialized generics are backwards compatible with legacy bytecode. The JVM handles the compatibility. Of course, the newer bytecode is not forward compatible with older JVMs.
Regarding the 0 value choice in Go, I don't agree that this is worse than null. It simply applies a design constraint that is not usually very hard to satisfy - that the 0 value of your type must have well defined semantics.
If you allow a nonnull field to hold null at any point then it's trivial to leak that out and have nonnull variables holding null all over the program, which is obviously something to be avoided.
Maybe you can say that if you read a nonnull field when it's null, that throws an exception. That might have its own knock-on effects since nobody expects reading a field from a valid reference to throw an exception, but it might be the best way.
Of course, as I said, this ship has long sailed for general Java classes. It would be far too big of a breaking change to add such a limitation today. However, we know for sure this could have been done in Java: this is exactly how record and now value classes work: any call that could expose un initialized fields is in fact disallowed.
There's a whole bunch of specification language describing how constants aren't actually constant in specific situations.
I don't know Kotlin but I assume it does the same thing: until the non-nullable field gets initialized, it holds null and violates the type system.
Kotlin still has a hole where you can run code in "init" blocks which are executed sequentially on object construction; in one, you can call a function that is defined after an unmodifiable property, and it will see the uninitiailized value.
also, null markers are coming too: https://openjdk.org/jeps/8303099
Its just that they have to deliver things incrementally. This PR that introduces value classes/objects is already 200k lines long.
I think you've missed what this is referring to. It isn't about null safety (which is orthogonal) but about having reference/value projections analogous to Integer/int.
What the Valhalla team ended up doing is, instead of having two projections for each type, one with identity and one without, value types never have identity and so Integer and int are synonymous, and the memory layout is determined automatically based on context and optimisation decisions. This is why the semantics of == for the primitive wrappers (like Integer) were changed, as they now don't depend on whether the "reference projection" or the "value projection" is used.
> There is no reason to reduce the optional(!) safety guarantees you can offer with the excuse of "too mentally taxing".
This is not what happened here.
Except they're not, as I can do Integer x = null, but not int x = null. So an Integer is forced to occupy more memory, for very very unclear reasons. And this is also deeply weird - there is no other (mainstream?) language that allows null value types.
Yes and no, because in Java we have runtime types and compile-time types. The frontend compiler will treat these types as having different defaults on nullability, but they'll compile down to the same representation (when appropriate). I.e. if the compiler sees that some Integer variable is never null, it will compile down to the same thing it would if it were declared an int.
You're right, however, that on the heap, until the language adds nullability information, the compiler cannot generally know that an Integer will never be null (unless it's a final field), so it's likely that, unlike on the stack, you'll get a different representation.
That goal is an ideal and can't be reached perfectly. Converting a type to a value type will break clients that synchronize on them, or rely on identity for some reason. But such cases are rare, and can be weighed up on an individual basis when making the decision about whether to do it. Storing things in a nullable variable on the other hand is very common and changing the rules to prevent it would make every such change a source incompatible breaking change.
If you have language-wars about a concept going in and out of existence, that is a hint that there is demand and the language does not properly handle the demand or when it handles it, it creates mental overload.
> Value
> Errorstates
> Null
> IoExceptions
> WeirdOsStatesNeededToHandleUpstairs
As the pythons said: Get on with it!
That said, we've been gnawing on this limb for a while...
This takes longer than game of thrones books
What? It’s been getting better with each release. Valhalla brings features that address key problems, and they didn’t rush to it either.
This seems heavier? Having two representations and manually having to refer to .val or .ref?
You can argue that the extra flexibility lets you write safer (non-nullable) code but naively it seems more complex at the language level.
Saying the mental model is too hard is basically saying your userbase is stupid. This stuff is not tricky.
How much was this article proof-read? Didn't they just get finished talking about how heap flattening won't work for objects with > 64-bit representations? Their `Point` is at least 65 bits (two 32-bit ints plus the null flag). The "plus a possible null flag" and oddly short following statements seem to suggest this was some AI that got sidetracked by trying to make emphatic statements... oh and also the "[IMAGE: the same Point[] array in two variants..." block halfway down the page is unfortunate.
that smells of AI [1], and thus lazy writing. I'm all in for using AI to help you write, but if you don't put your voice to it then there's no reason to read it.
[1] https://en.wikipedia.org/wiki/Wikipedia:Signs_of_AI_writing#...
Don't be all-in. It's important for humans to be able to write for themselves, and also to stand by what's been written in their name, which is much less likely if someone/something else has done the writing.
(proofreading is another matter though.)
As a proportion of all easily crawled text on the internet, a lot of it will be random marketing copy. That influenced the writing style of early AIs, and since then everyone has trained at least partially on transcripts from every other AI chatbot
Like Caesar's supposed "Veni Vidi Vici" saying, people seem to prefer and remember items when grouped in three.
I recall a public speaking film shown to my management science class starring John Cleese mentioning this rule of 3.
Nope! That is - training on lowest-common-denominator, low-signal high-noise "idiotspeak" was not at all inadvertent.
4chan
Call of Duty chat logs
Every public marketing site
SlashDot
UseNet
...
Verdict: Yes idiotspeak was part of the training set, but no, it was not inadvertent. There's a smattering of Shakespeare in there, at least.
It stopped being infuriatingly sloppy and took time to ensure the article had integrity.
It did having said that I did burn through a lot of tokens trying to do a deep analysis cross data pipeline debug.
Please, if you write a technical blog, or anything really: Stop. Stop letting the AI write for you. Nobody wants to read this.
TIL that Rust has NonZeroU64 which you can combine with Optional to get the required behaviour with only 64 bits per entry. [1]
Also, apparently, shifting a negative number to the left is UB in C.
> a lot of things... would make much more sense as implementation defined.
Or even just defined. Apparently, the fact that shifting right a signed number is done arithmetically, not logically, is implementation-defined too.
Well, at lest bitwise not/and/or are (almost) fully defined even for signed integers, so that's something.
Luckily we have Valhalla, which is an admission that Gosling was partially wrong, and programmers who want to have an unsigned nullable non-zero 64-bit integral value type can just make one, and not have to pay outsized memory costs to do so.
If we're done paying homage to Gosling, can we get operator overloading for our fancy value types please? I have no idea if this is on the radar for Valhalla.
> On June 15, Oracle engineer Lois Foltan confirmed what a good chunk of the industry had stopped believing: JEP 401: Value Classes and Objects will be integrated into the main OpenJDK repository and is targeting JDK 28.
> The change is so large that the remaining committers were asked to hold off on bigger commits during the integration. The pull request alone adds over 197 thousand lines of code across 1,816 files.
What in those paragraphs is obviously AI?
« The pull request alone adds over 197 thousand lines of code across 1,816 files. »
I noticed that both Claude and GPT are fond of those kind of stupid accounting statements that don’t mean a lot in and of themselves, but look impressive in a « wow numbers » way. Which is kind of ironic since counting remains one of their weak points
For instance I might write this "The pull request alone adds nearly 200 thousand lines of code spanning almost two thousand files", or even better just "The pull request alone adds nearly 200 thousand lines of code" because really who cares how those are broken up into files.
It said "over 197 thousand". That's what I'd probably say for a number in [197000, 197999], or maybe "under 198 thousand depending on where it is in that range.
Saying "nearly 200 thousand" is still 3 digits so doesn't save any space over 197 or 198, and I think with it only being 3 digits most people will assume only the last digit is rounded. 200 ending in a string of 0s does suggest it might be rounded to the nearest 10 or nearest 100, but it just could easily not be.
I'd almost certainly fully write out 1816. If it were common to spell out groups below 1000 like 100s and were going to that I might write it as something like "just over 18 hundred" or "almost 19 hundred", but I almost never see anyone use grouping sizes of less than 1000.
By necessity a lot of people write very similarly to how llm do
People care about provenance a lot.
Whether it’s a drawing my daughter did of her mother, a Picasso napkin sketch, a worn 1960s Stratocaster, or an blog essay, the provenance is value on top of the correctness of the item.
But you don't know which parts of it are true.
In this initial commit. As was made clear in the JEP, this is just the first deliverable of a huge feature that, like all Java features in recent years, is being delivered piecemeal. Obviously, the point is to flatten larger values (the mechanism is already in the JVM; what remains is exposing the intent of "I allow tearing" in the language).
Looks like they just missed the `!`. It should be `Point![]`.
Is there a way we can request a "flag as AI garbage" downvote for articles? Or should we just flag them?
It adds a fair bit to that "did anyone proof-read this? pretty obviously no?" vibe.
Our work uses modern Java (26 w/ preview features - mainly for StructuredConcurrency), and it's fantastic. Do not regret it one bit, and that's coming from using both Haskell and Python at previous companies.
Good news is, Oracle extended extended extended support for Java 8 will not last forever, and eventually - if you work in a regulated industry - the company WILL have to pull the trigger.
On the other hand, "where there is muck, there is brass", so a little bit of legacy can be beneficial for some.
There's something else amiss here. Compared to other platforms, upgrading Java, even on complex codebases, has never been a nightmare for me.
I upgraded a codebase of approx 100 kloc from Java 7 to Java 8 a couple of years ago. As I didn't want mixed patterns for the same thing throughout the code base I replaced most of the loops with their streaming equivalent. I had the luxury of having the budget for doing so.
Mixing patterns of newer language features alongside older ones can make the code base hard to read.
If Java was a child, imagine it being brought up by loving parents for the first few years (Sun) then it was thrown in a garage with some other children and neglected by its evil guardian (Oracle)
Neglected and unloved till JDK 8, its basically been playing catch up.
So when people say "oh so its now got structs or value types of X", yes it has but that's because it has been stunted in its development due to big bureaucratic and hostile corporate processes, but its free now and is getting love through the OpenJDK family.
I will continue to enjoy writing once and deploying anywhere!
Whether you like oracle or not, this is simply not a correct description of Java's history. It was brought up by loving parents, who due to financial problems had to put Java into a foster home where she was neglected.
But later it was adopted by new, loving parents (Oracle) and she bloomed and become a healthy and stable adult.
Like, it was Oracle that completed the open-sourcing of the platform, making OpenJDK the reference implementation. They also open-sourced the previously proprietary jfr, mission control etc tools.
They also managed to keep many of the original members of the language team, which is quite rare during these acquisitions, and Java has seen a huge improvement both on the language and runtime front.
The Java team has been delivering nice language and environment improvements regularly since Java 10.
Same with MySQL, btw. "Dead" according to this site, risen from the dead under Oracle for those who actually know it.
In fact, much of the software industry, which writes the software that matters to our lives the most and holds most of the value delivered by software in general - the software that processes your credit-card transactions, runs your bank, sorts your mail, routes your phone calls, manages the manufacturing of your car and the shipping of your packages, holds your healthcare information, schedules and tracks your flights, and manages your law enforcement and your government - is barely represented here because the organisations that write most software aren't software companies, and they don't tend to publish technical blogs.
People come to HN because they want to hear or talk about things that most people don't usually do; it's more interesting because it's different! I'm not saying they always say positive things, but positive or negative, this is what we like talking about online. This is why people buy GQ or Vogue. If you want to talk about boring work stuff, talk to people at work :)
> Neglected and unloved till JDK 8, its basically been playing catch up.
These two statements are contradictory. The last Java version under Sun was in 2006. Oracle bought Sun in 2010. JDK 7 came out in 2011 and JDK 8 in 2014.
The team largely remained the same, and the main difference was that Oracle ended the neglect and funded us more, which is why Java picked up the pace after the acquisition.
> its basically been playing catch up.
Catch up with who or what? There are only two languages in the world as popular as Java or more: JS/TS, and Python. People who are saying Java is "playing catch up" usually compare it to languages that are doing far, far worse than Java. It's just that people who like certain features think that the language that has them is doing poorly despite them and not because of them. Many times I see people insist that other languages are "doing it right" (or better than Java) even though it is clear that the people who say this are in the minority when it comes to preferred features.
> So when people say "oh so its now got structs or value types of X", yes it has but that's because it has been stunted in its development due to big bureaucratic and hostile corporate processes, but its free now and is getting love through the OpenJDK family.
If anything, the opposite is the case. Managers love to see things ship quickly. It is our technical leadership - all people who were there in the Sun days - who insist we have to move deliberately and carefully and get things right. You can agree or disagree with the decisions, but comparing Java unfavourably to languages that are doing far worse is unconvincing.
Rather, what I think the vibe is because Java is not as popular as it was in, say, 2003. And it certainly isn't. But guess what? No other language is, either, because that time was anomalous not only for Java, but for the entire software ecosystem, which had never been as consolidated and unfragmented before or since.
Except to the browser, iOS, embedded systems...
WebAssembly is the real write once deploy anywhere tech now. JVM had its turn and lost.
Serious question: I remember the old installer, six billion devices or whatever. I’ve heard about Java ME, old set-top boxes and DVD players, etc.
But how much of that is active today. I can’t say I’ve ever seen a job listing for an embedded Java developer or even Java ME in my entire career. Are people actually still using it?
Weird but true, and quite obscure.
ISTR Siemens uses wasm2c to compile Wasm for a bunch of embedded devices runninng Zephyr RTOS.
Anyway, I wouldn't even call Java "stunted". It made choices, some reasonable, some not, and those are incredibly hard to fix later. Heck, just look at C++. Semi-compatibility with C is (IMHO) an unfixable 150 foot albatross around its neck and so many versions from C++11 onwards have simply been about making that 150 foot albatross more bearable.
I personally think treating all value classes as a single L-type in the JVM (like primitive types, basically) is a fairly neat solution to a difficult problem. But all this comes down to the original Java 2 decision to implement generics as type erasure to maintain backwards-compatibility, something that C3 NOPEd out of as a result.
I’ve been reading the mailing lists and watched all videos on the topic and it is truly inspiring how much they managed to consolidate the design to something that always looked like java.
But while also going far deeper in granularity and understanding what it even means to be a value type and what optimizations can be done where
So == for value classes will basically be like memcmp(). That is a bit unfortunate, as it breaks encapsulation, exposing implementation details. Client code can use this to do case distinctions based on how a given value is internally represented. In a way, it’s worse than identity comparison, because identity comparison at least doesn’t expose internal state.
To see why, consider that to do any useful work, data from different objects (also from different types) has to be combined. To be able to do that in the OOP framework, the encapsulation has to be unwrapped. That's why Java code is littered with getters and setters that don't do any useful work at all, they just make it too painful to get any real work done.
Again, there is a place for objects and implementation hiding, but it's at the highest levels of an architecture where different components get integrated.
This also has huge implications in a language that emphasises dynamic loading like Java. And it also flies in the face of all of the pretenses that ABI compatibility is sacrosanct and no feature that breaka it can be considered, that the design team often touts.
But I'd say that GP's complaint about inequality leaking makes no sense anyways, because what could be more unequal than different implementation, or different internal state implying different behavior down the line? The public subset isn't some arbitrary interface that could have different implementations. And even then, "equals under interface I1" would have to be considered a very special type of "equality", not the general case.
The JEP also gives examples of classes where == would return false for instances that would behave exactly the same from an external perspective. They give examples mostly revolving around strings and other reference objects as fields of value objects; and some weirdness around float and double NaN. There's also the classical case of caching, where an object may store the inputs to a complex calculation, but can also cache the result of said calculation - and asking for the value can either perform the calculation, or return the cached result (though Java value classes don't fit this too well, given their limitations of being immutable).
Java separates checking identity and equality for objects. == basically checks if two pointers are the same. Equality is a subjective concept based on an interface (ie equals/hashCode). So this means:
new Integer(1000) == new Integer(1000) // true, used to be false
new Integer(1000).equals(new Integer(1000)) // true
new Integer(10) == new Long(10) // compiler error, used to false
new Integer(10) == new Integer(10) // true
You may still be able to get the old behavior through variables too.
Anyway, if value classes lose identity then == changes from pointer equality to bitwise equality. That will hopefully resolve a bunch of corner cases like this but it is a breaking change, technically.
new Integer(10) == new Integer(10) // true
https://github.com/openjdk/jdk/blob/jdk-27%2B27/src/java.bas...
iconst_1
invokestatic java/lang/Integer.valueOf:(I)Ljava/lang/Integer> By default, Java maintains a cache of Integer objects for values between -128 and +127.
[1]: https://stackoverflow.com/questions/3130311/weird-integer-bo...
[2]: https://dev.to/marzuk16/understanding-integer-caching-in-jav...
Years before the autoboxing/Integer.valueOf() caching stuff (and before generics), (I) used to have IntegerProvider that did similar stuff to higher ranges. Personally, I have considered autoboxing on integers net-negative for Java
wait, really? I thought introducing _such_ incompatibility was not allowed
It should work even for strings: They will surely continue to be heap-allocated, and memcmp-ing pointers (inside the new "structs") is exactly an identity comparison.
For example, you might have a value class for representing (limited-precision) fractions using two longs internally, for the numerator and denominator. For efficiency trade-off reasons, you don’t want to always shorten the fraction. But now client code can distinguish 2/3 from 4/6 using ==.
Scenarios of that sort are conceivable where this actually leaks sensitive information. In any case, it creates dependencies on implementation details where you don’t want to have them.
When designing a value class, you are now in the dilemma of either always having to normalize the representation, costing performance, or having your class be a funnel for leaking implementation details.
There is a lot wrong with that: complexity, bloat, and slowness.
> But now client code can distinguish 2/3 from 4/6 using ==
That's a great way to obfuscate code. Not a good idea. The right way to do the comparison is, just make a function called CompareRational().
They want basically to solve the main Java design flaw with (almost) everything is a reference paradigm. C++ and Rust have had value-types from day one.
> 64 bits, including the null flag
So, this basically makes every value-object optional, adds extra overhead and makes code less safe to null pointer dereference errors.
> but a class with, say, two int fields or one double may not fit in an atomic write and end up as an ordinary object on the heap anyway
So, the whole optimization is applied only for very small structs with no more than two scalars (or so). Did it worth to spend 10+ years of development to achieve this?
Java JEPs are piecemeal, there is plenty other JEPs building on top.
Value types, generic specialization, boxing - a quick skim makes it looks like they picked the same choices.
So where in other languages, the struct/class taxonomy is binary, Java allows more granular control, reflection the semantics of the underlying domain. Snd as it turns out, structs have a wide range of footguns, especially in a parallel context.
For example, Imagine you have an api like `void do(List<Foo> foos)`. In the erasure environment of the JVM that looks like `void do(List foos)`. From python it's pretty easy to call with a `foos = [Foo()]`. But not so much if your python implementation needs to figure out how and if it can coarse it's `List` type into a `List<Foo>` type.
Having reified generics in the CLR just lets you store more type information. There isn’t much of a trade off for CLR end-users.
Compare this to the constraints and workarounds that Kotlin and Scala have due to type-erasure on the JVM.
The creator of Scala disagrees: https://youtu.be/Xn_YpUtXWT4?t=850
The monomorphization of CLR generics is what NativeAOT does, though it doesn't support some C# features.
TypeScript is essentially C#, but with type-erasure and lacking the low-level struct & pass-by-reference features.
I do think the C#/CLR struct implementation is better though.
And as far as I'm aware, both kotlin and Scala don't really suffer due to type erasure.
That being said, it is easier to write a language on top of the JVM with good interop, since there are less ways to implement features. Essentially, your language has to interop with Java.
And it is harder to have good interop between CLR languages because there are more ways to implement features. Essentially, your language has to interop with C#.
Nowadays largely abandoned, and I think not everything survived the transition from .NET Framework into modern .NET.
The DLR is not "abandoned" so much as "complete". Everything did survive the transition into modern .NET and IronPython 3.4.2 runs just fine on .NET 6+ [1]. (For those trapped on the ugly side of the Python 2/3 split, even IronPython 2.7.12 runs on .NET 6.) Most of the "magic" of the DLR is shared with C# Linq in interesting ways (the System.Linq.Expressions AST) and sort of "has to survive" if only to properly support IQueryable<T> (and wilder relatives like IQbservable<T>, the Q is not a typo) even if most people aren't actively using DLR languages today (nor that much usage of C#'s `dynamic` keyword).
IronPython is a community supported (truly open source) language so doesn't get as much attention now as it did in the brief "first party" support era, so some may call that "abandoned" but F# has always lived in that gray space where it is primarily "community supported" more than "officially supported" by a dedicated team at Microsoft.
[1] https://github.com/IronLanguages/ironpython3/releases/tag/v3...
Even though most of the communication around dynamic was about COM support and Excel.
The COM support is by implementing IDynamicMetaObjectProvider in a cross-language reusable base class.
The C# `dynamic` keyword adds some smarts about IDynamicMetaObjectProvider to the C# compiler, but those smarts were never seen to be needed as a low level tool in the CLR itself. And again, once the C# compiles the IDynamicMetaObjectProvider calls, those mostly just result in System.Linq.Expressions for the JIT compiler to optimize in the same way it optimizes other usages of Linq.
I suppose DLR would be comparable to GraalVM/Truffle.
The difficulty of implementing a dynamically-typed language directly on the CLR and JVM are about the same. Though, it would probably be more efficient on the CLR with access to lower level operations for memory management.
I think an interesting project would be to implement a CIL interpreter on GraalVM.
GraalVM already handles LLVM bitcode, much cooler than plain MSIL.
And here there is another example where Java ecosystem ends up being better.
MSR had a compiler framework similar to GraalVM, called Phoenix, it was going to replace VS, LLVM style, instead it died and what is left are a couple of research papers.
Anonymous classes are still used (sometimes). It simply depends on the circumstance of the lambda.
For example, this will result in a new anonymous class being generated.
void foo(String s) {
stream.filter(i->s.equals(i));
}
What won't generate a new anonymous class is this sort of lambda
stream.filter(i->"foo".equals(i));
Never bothered to actually look into the generated bytecodes.
I was wrong, it looks like the case I gave is one which doesn't result in a new anonymous class being generated. Instead the lambda metafactory gets involved to avoid that allocation.
I apparently didn't see what I thought I saw. I thought that I had seen new `lambda.$1` classes being created in call stacks when debugging. Maybe I did, but the lambda was serializable (we have that in some unfortunate places in our code base).
There are still cases where new classes get generated, but that's pretty much just for serialization.
[1] https://cr.openjdk.org/~briangoetz/lambda/lambda-translation...
This is fine if you hand-roll all your code yourself, but I often use mapping libraries to lower the code footprint and the problems resulting from schema changes are subtle and fly under the radar. This is different from classes with hard construction guarantees, which Java would offer with their "integrity by default" mantra. Where you can opt out of integrity for performance benefits (which is also part of the design).
And Nullability in C# is an absolute nightmare. The type system has completely different rules for nullable types that generalize over classes and structs and there is no generic such as a "Nullable type".
It's just lots of minor annoyances that don't form a cohesive whole.
Structs are values, classes are entities with encapsulation.
The shape of the state would be structural. Whether or not the data in that shape is valid is behavioral.
Structs are useful when working with spans of memory.
Another example of a good usage of struct is Guid, which is 128 bits of data packed together.
The C# equivalent to Java ‘value class’ would be a class with a struct encapsulated for data. The data is flattened and allocated on the heap like Java. Similarly, escape analysis could stack allocate the class at runtime.
Structs in most languages simply bunch a couple constraints together to get another set of performance benefits, but there's no law stating that they couldn't be singled out. In the design of Valhalla, it states that types can come in 4 buckets:
1: Fully identity classes (total control, mutable)
2: Value Based classes (no mutability, but full integrity and dense memory layout)
3: Implicitly constructed values (forced empty default constructor for swift bulk array initialization)
4: Tearable Values (No cross-field integrity during runtime for parallel access)
And I bet that for a vast majority of developers, #4 will come to a shocking surprise, thinking "values are threat safe" because they are told to use immutables.
This way of splitting up structs is the real interesting part of Valhalla, but this shitty AI-generated article buries everything interesting.
You have to opt into force flattening, and then it’s the same as a struct, except it’s still heap allocated without escape analysis. You still have to implement synchronization to prevent tearing.
Static code analysis can give you a warning for potential tearing of structs.
DotNext.Threading provides Atomic<T> to enable high-performance atomic operations on structs without heap allocation.
https://dotnet.github.io/dotNext/features/core/atomic.html
The design of value classes just seems counteractive to its purpose: memory management. If I want to manage contiguous blocks of memory, let me manage contiguous blocks of memory. If I want to allocate something on the stack, let me allocate something on the stack.
The paradigms of struct vs object are too different and they’re trying to combine them into one.
Regarding #4, is this actually a done deal? I haven't dug into the JVM specifics, but I thought they would avoid allocating objects. And for now they just want to get the model right, while continue to optimize as time moves on. I think that's the right approach.
I actually see this way less critical because if you truly have performance-critical usage of structs, you know what you are doing. And if you know what you are doing, you will know about opting-in.
And for everything else? I think it's nice to have a range of benefits that come from having a value type without handing a gun to a monkey. Because the feature will be misused by people that don't know about tearing, thinking "value" is a free performance upgrade. And I do believe that it is the right mental model to reason about it.
I just don't see the huge issue. If the CLR has a way to provide atomic access to non-tearable structs, surely the JVM can too? We are talking CPU instructions here after all. Or am I missing something?
For me, a struct in C/C# can be modified and is passed by copy while a value class can not be modified and is passed by value.
I do not think you can do stack allocation in Java.
C# copies C++ behavior where you can pass a struct by value or reference, and you can mark the parameter as readonly. C# also has in/out parameters. Essentially, you can program in C# exactly like you would in C++.
https://learn.microsoft.com/en-us/dotnet/csharp/language-ref...
The footgun with C# structs are that you can accidentally box them onto the heap. To avoid that you can define `ref struct`s that cannot be boxed. `ref struct`s follow the C# disposable pattern.
https://learn.microsoft.com/en-us/dotnet/csharp/programming-...
https://learn.microsoft.com/en-us/dotnet/csharp/language-ref...
The mutability difference is that part of a struct can be modified in place, which value classes can’t: the value of a complete value-class variable (or array slot) can only be modified (reassigned) as a whole. This is presumably because object references to value-class objects can be created, and those objects should be immutable so their identity doesn’t matter.
The other solution is to stack allocate and pass a pointer but as i said, unlike in C#, i do not think it's possible to do that in Java.
In Go, you can stack allocate but when you send a pointer (that escapes), the compiler will heap allocate the object.
People really misuse/misunderstand this term: Java objects are passed by their pointers ("references") being copied.
The alternative is pass by reference, which is done by e.g. c++, rust, who actually have references (Java doesn't). A good litmus test is whether you can write a swap method that actually changes your local variables.
I do not know how this is called.
But under the hood it can (and will) do a modification in place.
The ramifications for backwards compatibility is that the JVM won't have CLR features such as stackalloc (allocation of blocks of memory on stack), ref parameters (pass-by-reference of stack allocated value types), and all the other low-level/high-performance programming features available in the CLR.
Why couldn't it be done? Like sure, it won't happen in every case (e.g. too big value classes), but for a typical local variable of a value type, it's a trivial optimization to make it stack allocated. Even now it happens quite often (requires escape analysis), but the semantics change of value classes allows for it to be done "freely".
Java chose to go with an L-world implementation where everything is still a reference type on the heap, but memory management is more efficient via flattening. That’s why it’s a ‘value class’ and not a ‘struct’.
Primitive wrappers are scalarized into registers.
Stack allocated value types would have different semantics and is incompatible with the L-world implementation. Sure, they could implement it, but it would be the Q-world implementation that they decided to forego.
They can do automatic stack allocation for optimization via escape analysis as you mentioned. But, stackalloc is user allocated.
https://learn.microsoft.com/en-us/dotnet/csharp/language-ref...
Java ‘value class’ only flattens if the total size of the class data fits within an atomic read/write op. You can force it to flatten, but you may have tearing like C# struct.
The false dichotomy of
> A struct in C# has identity and mutation, so the semantics of copying on assignment or passing have to be precisely defined, which gives a heavier model for the programmer and less freedom for the runtime.
Doesn't really match with what they're describing. While yes, it will not have identity in a java class ref sense, it of course will still have identity in being a unique structure in memory at a certain address. This is just splitting hairs about Java nomenclature.
No, it will not. The design allows multiple objects to share one structure in memory across multiple records, or not have such a structure at all (see Scalarization in the article).
Yes. I fear you are missing the point.
Again, not trying to turn this into a .NET vs Java thing, I'd have been much happier if they reached some new and interesting conclusions.
Well, it is - because they had to make it with almost perfect backwards compatibility for one of the most popular languages with trillions of lines of code produced over decades.
Sure, adding it to a new language is not hard. Adding it to Java which has primitives, generics and boxing, finding ways that seamlessly cover the differences between objects and primitives, while trying to plan for the future is hard.
As a general note, if you come to the conclusion that one of the best designer teams on Earth "basically copied what .NET did from year 1 is not a good look", then maybe your mental model needs adjusting on how these stuff works? Java has a public mailing list, you can browse through the related discussions. Implementation is the least of these things. But I can assure you they most definitely know what they are doing.
At what cost? A key benefit of value types is improved performance but AFAIK Valhalla doesn't even let you pass them by reference. Efficiently passing them through registers is great but won't help you out with larger value types.
That's materially distinct from Java's model of basically dynamic loading already compiled class files. Though class files do have "editions", and there are extra code to deal with different versions. But still, it should be possible to e.g. send a new value class to an old library's class that has never heard of them, and that should just work.
Oversimplifying a big semantic and backend change to a huge codebase on which some of the most crucial customer and government and business systems depend on, and which has to be made as seamless, correct, and performant as possible, to "they just copied .NET", just because .NET has the same functionality, is an even worse look.
It's a "HN "Dropbox is just rsync + some scripts"-style bad look.
top-level page: https://openjdk.org/projects/jdk/28/spec/
JEP status: https://bugs.openjdk.org/secure/Dashboard.jspa?selectPageId=...
I'd really like to see someone trace related developments in C#, Swift, Java, and Rust, since they all have been racing to catch up to hardware, and I believe they are cross-pollinating.
(My concern is how all this will affect the FFI memory shares.)
But Java's value types are a higher level semantic feature, these objects may do a Copy or a Clone based on heuristics. So probably not the exact analogue but of course rust being a lower level language it can express where and when memory is allocated.
The `Point[]` in the image tag of your LLM output crashed your image generation post processing.
Sad. Hope they can do this by the next LTS JDK.
Given that the JVM could already do escape analysis and allocate regular classes on the stack in certain scenarios, it's very unclear what benefit, if any, this will bring for normal processors for anything except the base wrapper types - even after implementing generic support and nullability for value types in a future JVM.
It’s when they land next part (nullability) it will shine fully - particularly on the intersection of not null and value. Alternatively if they introduce tearable semantics it will also shine - it would be possible to still optimize array of value classes, even if they are nullable (for example by having correspondent nullability mask).
So they are taking right step in a right direction. They are just trying to land this incrementally.
I'm not sure the no-tearing rule is particular helpful either. Like, this is something folks get wrong all the time in regular java. There's plenty of places where we use unsynchronized classes and expect synchronization to occur in the containing class or other explicit lock. If atomic operations are a requirement, and non-atomic value types get turned into references, then value types seem pointless.
I fear we're getting something called "Value types" with none of the actual benefits of value types. Like "we heard you want something called value types so here you are". No, we wanted a way to declare arrays of structured values without having to deref pointers, or to store structures inline as a field within an object. What I've read seems to be not that unless the structure's total size is 63 bits...
I really hope they give an escape hatch for this. It will make it really hard to extract a lot of the benefit of valhala if you can't make a thread unsafe value class. It's also one of those problems that will be quite hard to run into. You basically need something like this
class Bar {
static Foo value[] = new Foo[10];
static void setFooFromManyThreads(Foo foo) {
value[0] = foo;
}
value record Foo(int x, int y, int z) {};
}
The solution is also simple, a `synchronized{}` block will fix it if you need to have a tearable class that's written from multiple threads.
But the other thing is that for SIMD operations, you really need flattening, and that really does typically mean having something like `Foo(double x, double y, double z)` in play. It'd be a shame if the way we have to do this is a struct of arrays.
That's the tearing problem.
It gets worse because things you can't generally do in the JVM can happen. For example, if your value class contains a reference to an object but that reference just so happens to split a tear, it's possible one thread to see an invalid reference while another thread is writing that object. That could be fixed with some added padding based on the architecture to make sure stored references aren't tearable.
But tearing may still cause a logical issue of course. (Think of a date class where the day may still be 31 but the month was set to Feb on another thread).
Interestingly Go is memory unsafe on this issue, slices can tear and later code can read into an incorrect offset from the pointer. Java abstracts away pointers, so this issue is non-existant there.
You can assign the object again to overwrite it 'in place'.
> And a simple write-lock bit for fat Value Types would solve everything while maintaining most of the performance benefits (both on read and write)
They even already have an extra 'null' bit tacked on to the value object.
> In 1995, a memory access cost roughly the same as a CPU operation
Uhm... no?!
Here's a CS paper from 1993(!) about prefetching from cache(!!) because the cache was slower than the ALU. https://www.eecs.umich.edu/techreports/cse/93/CSE-TR-152-93....
It would perhaps make Java look a little bad to say that, in 1995, the prevailing attitude in certain circles was "If it's too slow, just wait for faster hardware - Moore's Law forever baby!" (Of course, Sun was selling, at the time, relatively fast hardware - the slower the software, the faster the required hardware)
The Z80 took 3 cycles to load from memory. A register to register transfer took 4 cycles (including fetching the instruction). Only one of those cycles was instruction execution.
I think the only reasonably mainstream scenario where the CPU would be significantly slower than memory would be the serial CPU designs such as the PDP-8/s.
That said, at the time people were doing cool stuff with 8-bit CPUs, they weren't running software remotely like what we're discussing here. That would have been done on a VAX, which had instruction and data caches.
What really happened, that the article is alluding to is that memory didn't get much faster in absolute terms since the 1980s. CPUs on the other hand did.
E.g. in the 1980s we had 60ns DRAM. Today DDR5 I believe allows about 10ns random access reads best case (6X). Over the same period CPU clock speeds have increased from about 8MHz to 5GHz (600X).
If I have a function that has a value `x` that erases to `java.lang.Object` (e.g. a parametric function with no lower bound); then it used to be safe to check for nullity and then synchronize on the object.
This is no longer safe: This can now throw `IdentityException` into your face. (it was _never_ a good idea)
In other words, a lot of old code must be reviewed.
I suspect that `-XX:DiagnoseSyncOnValueBasedClasses=2` will need to stay (with the semantics: if user tries to synchronize on identity-less object, then log a JFR event and make it a NOP, don't throw an exception)!
The current JEP text is a little too ambiguous to figure out whether that is the plan, anyways.
What will this code print:
Point a = new Point(10, 10);
Point b = a;
a.x = 100;
System.out.println(b.x);
This is a violation of the principle of uniformity. In The Psychology of Computer Programming, Weinberg explains that uniformity is a psychological principle which says that users/programmers expect that things that look similar should do similar things, and conversely that things that look different should do different things.
If a programming language lets two constructs look nearly identical at the use site while having meaningfully different semantics, it increases the cognitive burden on the reader. Programmers must inspect the type declaration or rely on tooling to understand whether assignment, equality, identity, and mutation behave like ordinary reference objects or like values. That can make code harder to reason about and maintain.
This could have been fixed by requiring the use of the "value" keyword not just at declaration time but also at use time like this:
value Point a = new Point(10, 10);
Point b = a;
a.x = 100;
System.out.println(b.x);That is, the situation you are afraid of should be impossible.
But the distinction still matters. Value-vs-reference semantics affect equality, identity, nullability, arrays, collections, boxing, and performance.
So this is not just an implementation detail. If a language hides that distinction at the use site, it increases the burden on the reader and makes code harder to reason about.
To avoid copying you have to explicitly declare a ref variable/parameter.
You can get the same immutability as value classes by using ‘readonly struct’s or ‘readonly record struct’s.
Java value classes are stranger because they are heap allocated by default and are only flattened/scalarized/stack-allocated when certain conditions are met. It’s the same as a class, but with extra restrictions, so that the JVM can possibly optimize memory layout at runtime.
No, there’s no way to know from those four lines that will happen, but we have that problem today. If Point was a record the same thing would happen.
value Point a = new Point(10, 10);
value Point b copy= a;
a.x uniq= 100;
System.out.println(b.x);
Since when? I’m pretty sure structs didn’t have identity last time I used C#, and that would be a very surprising thing to add.
If you want to change an element of such an array you need to create a new immutable struct which in practice it is quite fast, but a bit verbose to write.
That seems off. They're still objects, the new thing is that they can give up identity.
If sane generics had been introduced, the non-generic collection types would be a historical oddity by now and we wouldn’t be talking about how a future enhancement is going to undo the erasure decision.
Scalarization can fail in surprising ways just due to what a maximal atomic write can be on the target platform, and then it fall back to heap allocated objects.
Even if there's type erasure.
I much rather have the compiler balk at me than let me write something that may or may not work as expected.
if you really want a fun drawing get a human artist to do it. it doesn't need to be complicated, for example https://www.code-cartoons.com/ is mostly just stick figures and does an excellent job
but you don't even need any of that, a mermaid diagram would have worked perfectly fine too. instead you chose to use a technology that is known to be harmful
If you don't have the time or put in the effort to make your article, I'm not going to spend time and effort reading it. You really don't need some generic cartoon guy hovering over your graphs, draw them in MS paint or something.
1. Can someone remind me why it was so important/intentional at the start of the language that every object has identity? 2. Why is it important that we not synchronize on these value objects?
Not sure if it covers exactly the same terrain, but perusing the article, it seems to be the case, with a single instance being the degenerate case.
I've made something like this in the past. And I did it exactly because `List<Foo>` was too expensive and slow.
class FooSOA extends Collection<Foo> {
double x[];
double y[];
double z[];
Foo get(int index) { return new Foo(index); }
record Foo(int index) {
double x() { return FooSOA.this.x[i]; }
double y() { return FooSOA.this.y[i]; }
double z() { return FooSOA.this.z[i]; }
}
}What is unclear to me is why the decision to use a Point instance as a value or as a reference is made in the class definition rather than by the caller.
> Point[] point = new Point[10];
For the same class, I might need an array of values in one place and an array of references elsewhere within the same codebase.
Conversely, if it auto-copies now you have to contend with runtime state changing the pass semantics?
Let's take a stroll down memory lane. First of all, .NET literally started as a Java copy. On top of it, a non-cross-platform one for almost two decades! After having shamed Linux for so long Microsoft finally started porting .NET to other platforms in a non-backward compatible way. A lot of .NET proponents will tell you porting from legacy .NET to .NET Core (which was renamed once again to .NET) would be a quick fix, but it isn't. For example, the shop I used to work in had some important cryptographic libraries which were very painful to port. And then, there's .NET's simplistic garbage collector, which can be quite annoying because it tries to be a one-fit-all solution that basically cannot be tweaked at all, often resulting in unresolvable latency problems. There’s a lot of other stuff, like its ghetto-like ecosystem and the insane fragmentation of GUI libraries.
I also don't get the C# praise. Over the years, it has become quite the bloated language. It feels like Microsoft tries to implement every feature possible without realizing that an enterprise language is supposed to be streamlined. Async/await? Very ugly, very annoying. Java has solved this a lot better with virtual threads and structured concurrency.
I could go on, but these "language wars" are silly and pointless. Both platforms have their pros and cons. Besides, I have a lot of bad things to say about the JVM as well, but it's nice to see Valhalla finally beocming reality. Too late for me personally though.
Like what?
legacy .NET to .NET Core (which was renamed once again to .NET)
here's .NET's simplistic garbage collector ... it tries to be a one-fit-all solution that basically cannot be tweaked at all
No, it was not. What's called .NET now used to be .NET Core. And then there's .NET Framework which was commonly known as .NET.
> "cannot be tweaked at all"
Are you serious? Not only does the JDK have multiple GCs for different use cases (Serial, Parallel, G1, ZGC, Shenandoah), they have very refined tuning settings (https://wiki.openjdk.org/spaces/zgc/pages/34668579/Main#Main... / https://docs.oracle.com/en/java/javase/25/gctuning/garbage-f...). What does .NET let you do with the GC? Set the hard limit? Maybe turn on/off concurrent collection? That's not tuning, that's triviality.
Coming from someone claiming:
"language wars" are silly and pointless.
Language wars are silly and pointless. Someone tells me he/she uses language xyz, I basically don't care, do whatever works for you ,but God forbid you cross a .NET proponent. In case you haven't noticed, this is a post about Java. You mention Java, and the first thing that happens is a bunch of .NET maniacs popping up out of nowhere, telling you how Java copied this feature or how C# had that feature for years. What is this?
And that across 2819 commits.
Wow, that’s insane.
Java is generally backwards compatible, so unless you're using fat frameworks that use shady internals or known-deprecated APIs, you should generally be fine immediately upgrading to the latest LTS, possibly even non-LTS versions if you have confidence in your stack.
Mostly just hit the LTSes is what we've been doing and since about 17 it's been a pretty easy process in general.
Protip: If you ditch lombok everything gets a lot easier.
I do not think you can do stack allocation in Java.
-XX:MaxRamPercentage=70
1 comment
> "The defining trait: no identity"
I get that this makes objects behave like primitive types. Maybe thats reason enough. But is it necessary for the performance boost and de-fluffing the objects? Seems like an orthogonal objective
> There’s a catch worth knowing about here, though: flattened data has to be readable and writable atomically (otherwise it risks “tearing” under concurrent access).
Isn't this a race condition and "undefined bahvior"..? Having to limit yourself to atomic sizes seems like a huge limitation, to accomodate what is most likely buggy code. Is all the effort only gunna help lil toy ColorRGB examples?
> The points array is a million pointers. Each pointer leads to a separate Point object lying somewhere on the heap.
Does this happen in actuality? One would assume the allocator tries to put stuff sequentially on the heap? Its not a guarantee as with these Value Types, but I'd think you could get similar-ish perf with prefetching in cache. I dunno whats happening under the hood.. But when writing Clojure apps the JVM always reserves absurd amounts of heapspace on my machine (to my annoyance). Id assume it can find some place to do contiguous allocations..
Which i guess gets me to my last question... where are the benchmarks broski? It all sounds great, but does it actually yield the insane speedups promised?
Great article, well written. But a benchmark would have been a nice "punchline"
Yes. The one part of the JVM GC that can't run concurrently is heap compaction; objects that can be moved by copying and then deleting would be a huge help for that. And it would be awkward to say the object has an identity but can't be wait/notify'd, at which point you need somewhere for the monitor to go.
> Does this happen in actuality? One would assume the allocator tries to put stuff sequentially on the heap?
Yes. Of course it tries, but semantically the pointers are just pointers and the prefetcher can guess but the system still has to chase them.
It feels like an orthogonal objective and honestly arbitrary distinction, yes.
> Isn't this a race condition and "undefined bahvior"..? Having to limit yourself to atomic sizes seems like a huge limitation, to accomodate what is most likely buggy code.
I think they meant it like the appearance of atomic behavior from a java multithreading view.
> Does this happen in actuality?
Yes, it does happen. Having guarantees on this front leads to better performance.
> But when writing Clojure apps the JVM always reserves absurd amounts of heapspace on my machine (to my annoyance)
Might be a configuration problem?
Arguably flattening mostly makes sense for these only.
And yeah, you are right that allocations happen on something called a thread local allocation buffer, which is basically just a pointer bump in cost and objects allocated one after the other should be physically close in memory for the most part (though an object's creation may require a bunch of other object's creation that would sit in-between). But these have headers, so not as dense as they could be (though due to GCs being generational, they may end up actually closer in the next gen? The in-between temporary objects wouldn't survive for the most part)
The current code will help with `Integer[]`, `Char []`, etc, as well as combinations of `byte`, `char`, and `int`. Past that it doesn't really help much.
It would be fantastic if we could also flatten something like `Pair` or `Tuple`. However, even with compressed pointers, that is 64 bits, so that, plus the `null` bit, means it can't be flattened, which is a real shame. For various reasons, I have `List<Long>` in numerous places in my code, It would be great if that could also be flattened. However, since a Long is 64 bits, it _also_ can't be flattened. https://openjdk.org/jeps/8316779 would go a long way to to helping here, since then at least the null bit could be thrown away, which would allow more things to be flattened.
And then, if you want to go Wishlist land, something that would allow SSO (Small String Optimisation) would also be awesome, but that would require something akin to unions in Java, which we can _kind_ of do with sealed classes, but, since String is a final class, can't be retrofitted back into the language.
Does anyone know if Valhalla will flatten "simple" sealed classes, where every sealed class is small enough to be flattened? Since that would also be a powerful example to share.
In the current setup will a Pair Value Type be a compiler error, or will it silently just have bad perf?
Fun read.
Also, there is no exact analogue, C++ is just wholly different where you can specify copy/move/destruct semantics on a gradual basis.
Unless your company forces you to use Java for new projects, consider a change
I don’t know if this is fair way to try to disarm your critics. The only thing that’s remained after this decade is the slogan so it’s a real ship of Theseus question if Valhalla has shipped since what’s delivered doesn’t achieve it. Congrats on the accomplishment, but from looking at what ended up, I’m not sure it’s a huge improvement.
> The trouble is that this optimization is unpredictable and fragile.
Is this describing escape analysis or value classes? Because the list of exclusions where this does anything is so large and the conversion to a heap type under the hood is so transparent and opaque, I think it can describe this technique as well.
Also, the whole “works like an int” motto is violated - int is never null, int-> integer boxing is explicit and well understood.
> In the new model, the wrapper classes themselves become value classes (when preview is on, Integer, Long, Double, and company lose their identity
Oh neat, they sidestep that by changing the definition of an int. I’m sure it’ll be trivial to turn this on in the wild on code that may be relying on identity for boxed numerics. I think this alone shows this project can’t ever be turned on by default and now we’ll have a decade of two Java languages (one with value types and one without) as they try to convince everyone to migrate and then just turn it on (ie python3).
So much opportunity squandered and dismissing critics as always having something to complain about is a neat way to sidestep legitimate criticism that this approach is not going to work out for Java.