问题:

What is a "bag" in Java? I tried to find out from Google but I could not find a precise answer. I got idea from what I found on google that bags are similar to multisets. I want to know whether I am right or wrong because I didnt get proper answer through searching on google.

回答1:

Bag: Collection without order, may contain duplicates. The same as multiset:

In mathematics, the notion of multiset (or bag) is a generalization of the notion of set in which members are allowed to appear more than once.

from Wikipedia.

Note that duplicate is based on the equals( method in most JRE libraries.

回答2:

Core java contains no Bag class though the Collections interface does have this to say:

Bags or multisets (unordered collections that may contain duplicate elements) should implement this interface directly. (http://docs.oracle.com/javase/6/docs/api/java/util/Collection.html)

Other libraries such as Apache Commons Collections may contain implementations named Bag and Guava has Multisets.