有没有办法检查两个集合是否包含相同的元素，与订单无关？

Question

I've been looking for a method that operates like Arrays.equals(a1, a2) , but ignoring the element order. I haven't been able to find it in either Google Collections (something like Iterables.elementsEqual() , but that does account for ordering) and JUnit ( assertEquals() obviously just calls equals() on the Collection, which depends on the Collection implementation, and that's not what I want) It would be best if such a method would take Iterable s, but I'm also fine with simply taking Collection s Such a method would of course take into account any duplicate elements in the collection (so it can't simply test for containsAll() ).

Note that I'm not asking how to implement such a thing, I was just wondering if any of the standard Collections libraries have it.

Answer 1

Apache commons-collections has CollectionUtils#isEqualCollection :

Returns true if the given Collections contain exactly the same elements with exactly the same cardinality.

That is, if the cardinality of e in a is equal to the cardinality of e in b, for each element e in a or b.

Which is, I think, exactly what you're after.

Answer 2

This is three method calls and uses Google Collections Guava , but is possibly as simple as it gets:

HashMultiset.create(c1).equals(HashMultiset.create(c2));

Creating the temporary Multiset s may appear wasteful, but to compare the collections efficiently you need to index them somehow.

Answer 3

如果你想忽略秩序，那么如何测试集合是否相等？

new HashSet(c1).equals(new HashSet(c2))