A dynamic array that uses int not Integer objects. In principle this is more efficient in time, but certainly in space. This is simple enough that you can access the data array directly, but make sure that you append elements only with add() so that you get dynamic sizing. Make sure to call ensureCapacity() when you are manually adding new elements. Doesn't impl List because it doesn't return objects and I mean this really as just an array not a List per se. Manipulate the elements at will. This has stack methods too. When runtime can be 1.5, I'll make this generic.