What tialaramex is saying is that, in the Java code, there will be a separate allocation for every `a_goose` that gets added to the ArrayList, whereas the Rust code only has a single allocation for the backing storage for the Vec (not counting the resizes that occur as the ArrayList/Vec grows (both cases have ways to preallocate the proper size to avoid any resizes)). The context of this subthread is just to explain why someone who has Java experience might be prone to overcorrection when it comes to avoiding heap allocations.