Java has many types of Map, Set, and List implementations. And that's just in the core library. Here are some Map implementations that come with Java: TreeMap, a HashMap, A LinkedHashMap, ConcurrentHashMap, EnumMap. There are many more and they each have their own uses, features, and performance/memory characteristics.

I always wondered why languages like ruby, javascript, and python don't include a bit more choice on this front. It seems like sets are still somewhat of a novelty for javascript developers and people just wing it with half-assed solutions involving stupid O(N) contains operations.