Java Performance - ArrayLists versus Arrays for lots of fast reads

Question

I have a program where I need to make 100,000 to 1,000,000 random-access reads to a List-like object in as little time as possible (as in milliseconds) for a cellular automa

Answer 1

There will be an overhead from using an ArrayList instead of an array, but it is very likely to be small. In fact, the useful bit of data in the ArrayList can be stored in registers, although you will probably use more (List size for instance).

You mention in your edit that you are using wrapper objects. These do make a huge difference. If you are typically using the same value repeatedly, then a sensible cache policy may be useful (Integer.valueOf gives the same results for -128 to 128). For primitives, primitive arrays usually win comfortably.

As a refinement, you might want to make sure the adjacent cells tend to be adjacent in the array (you can do better than rows of columns with a space filling curve).