Guava MultiSet对比地图？

Question

我对Multiset的理解是一个有频率的集合，但是我总是可以使用Map来表示频率，还有其他理由使用Multiset吗？

Answer 1

Advantages of a Multiset<E> over a Map<E, Integer> :

• No special code required when adding an element that is not already in the collection.
• Methods for handling the count of elements directly: count(E) , add(E, int) , etc.
• The intention of the code is clearer. A Multiset<E> obviously maps the elements to their counts. A Map<E, Integer> could map the elements to arbitrary integers.

See also:

Multiset Javadoc

Multiset explained in the Guava Wiki

Answer 2

To me, the most important point that sets Multiset apart from a Map is that it's a Collection : you just put stuff into it and you can get counts later. It conceptually fits the use cases for which it's designed where a Map does not. For those use cases, a Map is just a hack that kinda-sorta works OK since Java didn't provide anything more appropriate.