HashSet and TreeSet performance test

Question

I read about how TreeSet is slower than HashSet, (that adding elements into a TreeSet is slower) so i made a performance test, i\'m trying to find out if it\'s better to add

Answer 1

Well, when you talk about peformance of TreeSet and HashSet you should clearly understand how these structures are organized what consequences of its organization.

Typically TreeSet is a structure where all elements are organized in a binary tree. Thus adding a member or accessing it is ~O(log(N)).

In other hand HashSet is a structure similar to an array. The difference is that in an array index is an unique number, while in a HashSet each key needs to be translated into index with the help of a hash function. A hash function may produce the same results for different input data, the situation is called hash collision. A good hash function (yes, they could be bad and good) produces as many unique results on a given set of input data as possible.

So accessing data in a hash set costs calculations of a hash function (in Java usually this is .hashCode()) and possible conflict resolution. That is its estimated as O(1) i.e. a constant number of operations.

You should understand that O(1) is not always less than O(log(n)), it's less asymptotically and on big enough n. Also a proper choice of a hash function does matter.