Why not auto-box Java primitive types for Generics?

So as far as I understand it, your proposed ArrayList<int> would be identical to ArrayList<Integer>. Is that right? (In other words, internally it still stores an Integer; and every time you put something in or get it out, it would automatically box/unbox it, but autoboxing/autounboxing already does that for ArrayList<Integer>.)

If it is the same, then I don't understand what the utility of having a duplicate syntax <int> is when it means the same thing as <Integer>. (In fact it will introduce additional problems, because for example int[] is not the same runtime type as Integer[], so if you have T[], and T is int, what would it mean?)

The generic type information is erased at run time. Check this link. Generics have more to do with compile time checking than run time checking. The autoboxing and unboxing are the run time operations. See the link. This is the reason that autoboxing should not work with Generics.