Is there a way to check if two Collections contain the same elements, independent of order?

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 Colle

Answer 1

If you want to ignore order, then how about testing sets for equality?

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

Answer 2

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

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

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

Answer 3

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.