Java speed comparison between HashMap and ArrayList

Question

I wonder if there are any comparison between searching elements in Hashmap vs ArrayList. The case which I encountered looks as follow: I'll have small amount of elements (usually 4-6 probably up to 10). I've integer Id of such element and I'll get a lot of calls which will search elements using id and execute some method on this element. It looks like good usecase for hashmap however I started to wonder if linear collection like ArrayList wouldn't be better here. For example because of CPU cache. And also to use search on map I need autoboxing to create Integer from primitive. Question is for this case better is do linear search and comparison of primitive ints or rather stick to hashmap?

Answer 1

如果您的 id 不是基于索引的，那么 ArrayList#get 将是O(n) （您必须遍历元素）而 HashMap#get 将是O(1) 。