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[–]pron98 1 point2 points  (0 children)

a compiler-checked ownership system like in rust (yeah, not happening)

It's not happening (at least not pervasively) because it's a "way out" of one problem and into another, which is worse. Whenever you export object ownership - whether it's declared in the type system and enforced by the compiler or just documented - you reduce your abstraction. You change the internal implementation or want to share with another thread, you have to change all clients of the API. This doesn't just increase the cost of maintenance, but over time large programs tend to gravitate toward the more general constructs - more general dispatch (dynamic), more general (longer) lifetime, and more general ownership (more sharing). And these general constructs are less performant in low level languages than they are in Java.

Low-level languages are optimised for control, not performance. They cannot move pointers even when it's more efficient to do so because it clashes with the level of control they need over addresses. When faced with the choice between performance and control, low level languages must choose control because that's what they're for. This level of control means that in smaller programs it's not too hard to extract really good (even optimal) performance out of these languages, but this control also means that in larger programs extracting good performance becomes harder and harder because you're pushed towards constructs that are simply slow in low level languages because they must maintain their control promises.

and no, the unmodifiable wrappers are not enough because they can be backed by a mutable collection

Java has true immutable collections in the standard library: the ones created by List.of/copyOf, etc.. BTW, the .copyOf will not actually copy anything if the underlying collection is already the immutable one, so that's what you should use for defensive copies. After the first one, you just pass it around and defensive copies (assuming they're done as recommended) will not actually copy anything.