Is it faster to add to a collection then sort it, or add to a sorted collection?

Question

If I have a Map like this:

HashMap map;

and I want to obtain a collection of values sorted us

Answer 1

Collections.sort uses mergeSort which has O(nlog n).

TreeSet has Red-Black tree underlying, basic operations has O(logn). Hence n elements has also O(nlog n).

So both are same big O algorithm.