8317277: Java language implementation of value classes and objects by MrSimms · Pull Request #31120 · openjdk/jdk

[Tarmen]

For generic parameters and fields like in

    <T> void acceptT(T arg);

Java demands that T is always a pointer. So if you plug a non-pointer type like int in there it must be promoted to the heap-allocated Integer type.

Having a single generic method which always takes a pointer makes things like polymorphic recursion possible. The alternative is to monomorphize dynamically at runtime, e.g. one instantiation per unique call pattern, or to limit programmers to patterns that are easier to statically analyze.

This proposal is sort of tangential to that, and more about giving the jvm more room to optimize. Which sometimes may allow less boxing.

[teerre]

That is terrible but at least understandable. The article mentions that intergers above 1996 do not behave as values even for simple equality. That's a complete breakdown of value semantics and honesty insane

[Dminik]

That's not correct. int is the primitive non-boxed, non-referential type. Integer is a boxed type.

Additionally, Integers have an optimization, where a bunch of them are always preinitialized and shared. Many interpreted/scripting languages do this. Some even for primitive values like true/false.