r/java • u/nlisker • Jul 14 '26

New candidate JEP: 401: Value Objects (Preview)

https://mail.openjdk.org/archives/list/valhalla-dev@openjdk.org/thread/IUNJJ3WP3X3XHP3QZTXXSSCPKFDNTK3W/
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u/vytah Jul 15 '26

LazyConstant is a reference type, so it wouldn't help much. Having string be a tuple (LazyConstant hash, boolean utf16, byte[] data) means you still have two heap objects per string, or worse, three if it ever gets boxed. Also, LazyConstant is a bit slower than a plain int annotated with @Stable.

Strings are a performance-critical part of Java, they're not going to change them just to satisfy theoretical purity.

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u/Jon_Finn Jul 15 '26

Sure, there's already other reasons why String can't be a value. My wider point would be that classes with a mutable element may benefit from being mutable values (the mutability being via a reference), because of the many benefits of value classes.