JEP 401: Value Objects (Preview) merged to OpenJDK master

mmfiguiere about 4 hours ago 30 commentsRead Article on github.com

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Discussion (30 Comments)Read Original on HackerNews

timmg•about 1 hour ago

I feel lonely in that: I mostly love Java as a language.

The lack of value types is the biggest impediment to certain types of performance. I am really looking forward to this evolution of the language.

MrBuddyCasino•19 minutes ago

Today it is a great language with a runtime that is unequaled. For heavy duty business backend server load, it is the standard choice, and rightfully so.

Do I love Spring? No. Do I prefer Typescript for my little side projects? Yes.

ludovicianul•11 minutes ago

I'm always amazed by how much thinking and work the Java leads put in rolling out changes that move the language forward, but make it backward compatible as much as possible.

parallax_error•17 minutes ago

Really cool, shame that strings can’t be fully indistinguishable like Integer despite their immutability

fallingbananna•7 minutes ago

Is there a theoretical reason why they can’t?

As a layman I would assume nothing is preventing it, other than the large amount of effort it would take to implement.

swiftcoder•about 1 hour ago

It's really nice to see movement here finally. Lack of value types has been one of the biggest performance pitfalls in Java for decades at this point

weinzierl•about 2 hours ago

If I understand this correctly then Integer becomes a value class and every instance of it loses its object identity.

I do not have a lot of knowledge about the details but from the outset it seems like a rather bold move to me.

agilob•about 2 hours ago

Java has a mechanism for Integer and Long objects caching using something that already looks like value object, cached objects can be compared using ==. hashCode of Integer already returns int, the boxed int value. Not much of value is lost.

swiftcoder•about 1 hour ago

Of particular note, all 1-byte Integers are interned, there is a pool of small Integers from -127 <-> 127 which are reused whenever possible.

I learned this the hard way, when a C++ JNI extension I was working on accidentally overwrote the pooled value for zero, and all hell broke loose...

agilob•12 minutes ago

> Integers from -127 <-> 127

The cache can be extended on startup with env var `java.lang.Integer.IntegerCache.high `

https://github.com/openjdk/jdk/blob/cc278dbb8a1ca0754d584270...

josefx•about 1 hour ago

Any project depending on Integer identity had years of warning that this change would come. Also given implicit primitive conversions and object pooling Integer isn't exaclty a prime candidate for object identity to begin with.

sheept•about 1 hour ago

It's pretty interesting that while both languages still receive new features, Java seems to stay ahead of JavaScript:

- Java has long had a modern replacement for Date, while JavaScript's recently standardized Temporal API still isn't supported in Safari.

- Java has switch expressions, while JavaScript, despite its Scheme influence, does not.

- And now Java is getting value objects, while JavaScript's equivalent tuples & records proposal has been withdrawn.[0]

JavaScript was not developed as a fork of Java, but much of its basic syntax still resembles Java, so I think it's fair to compare them.

[0]: https://github.com/tc39/proposal-record-tuple

HexDecOctBin•about 1 hour ago

What's the latest status? Is it still limited to 63-bits of data plus 1 bit for nullability?

DarkNova6•about 1 hour ago

Unless CPU instructions become widespread that allow to process 128 bits in one step, then yes. Java will have the same limitations as any other language. Other languages simply don't make this explicit.

spacechild1•11 minutes ago

IIUC value objects can have any size, it's just that 'reference flattening' requires the object to fit into a machine word. But this is only due to how Java represents object references and its atomicity guarantees.

Naturally, a language that properly supports value semantics does not have any of these limitations.

jeroenhd•21 minutes ago

We've had MMX for a while now, I don't think we need to wait much longer.

I don't really see why you would need specific hardware to express a type in a programming language, though.

jerven•11 minutes ago

Not for atomic writes, which is the important bit here. When dealing with concurrency the choice to make us will you allow tears when writing i.e. thread A writes aa and thread B writes bb. Will you allow the option of seeing ab or ba or only aa/bb. This is the thing that costs performance. Plus do you allow null which makes it harder too.

Smaug123•38 minutes ago

I don’t understand this comment - the .NET CLR supports arbitrarily large value types. Are you referring to something like “atomic flattening of those types” instead? Because the CLR doesn’t guarantee that, and therefore supports flattening.

ligarota•about 2 hours ago

The MR is closed

This is it https://github.com/openjdk/jdk/commit/cc278dbb8a1ca0754d5842...

germandiago•about 2 hours ago

2934 commits OMG... huge work.

andrybak•16 minutes ago

The way pull requests and commits work in the OpenJDK repository -- a bot squashes each pull request into one commit: https://github.com/openjdk/jdk/pull/31120#issuecomment-51378...

The final singular commit is cc278db (8389219: Implement JEP 401: Value Objects (Preview), 2026-07-31) https://github.com/openjdk/jdk/commit/cc278dbb8a1ca0754d5842...

fulafel•12 minutes ago

Is there a writeup on why they choose to destroy the history?

jerven•4 minutes ago

You can recover the history using their tooling build on top of their bugtracker and GitHub. Specifically they capture the discussions and all small changes over time in their skara tools and are prepared to leave GitHub if needed. They had multi de adres experience and had multiple prior code repos. Still do if i understand as the Oracle team has the sun and bea code repositories pre openjdk preserved.

thibaut_barrere•about 1 hour ago

Yes, massive respect for that type of perseverance on long term, important changes.

jurgenburgen•about 1 hour ago

Seems like a horrible way to work. Why could this not have landed as a large amount of smaller PRs in a more incremental fashion, maybe Java users could have gotten some value out of it earlier.

DarkNova6•about 1 hour ago

Out of all factors this certainly isn't it. If anything, more projects could learn from the way Valhalla was handled.

It started out as a highly invasive, highly disruptive and highly experimental branch that eventually turned into a beautiful specification that put semantics and performance payoff first and syntax seconds.

krzyk•about 1 hour ago

This is incremental. This change is the smallest possible one that could work. There are more coming in later.

estebank•about 2 hours ago

It's a project years in the making.

whytevuhuni•about 2 hours ago

How much of Valhalla is this? 50% of it? 90% of it?

pjmlp•about 2 hours ago

50% maybe.

There are other projects that depend having it in place, SIMD (vectors), reiffed generics, non nullable types.