I think the code also has the option to read and store the address. However I also think it would have other problems. Heaps with less than 4GB size would put a

I think the code also has the option to read and store the address. However I also think it would have other problems. Heaps with less than 4GB size would put a limit on possible hash code values and object alignment requirements would make it even worse, so you never get use out of the full 32 bit hashCode. Then you have generational GCs and if I understand those correctly you could end up with a lot of objects that started out at the same address and if you call hashCode on them before they are moved to a long lived generation you almost guarantee a large amount of hash collisions down the line.