Question

I discovered containsAll() (a List interface method) during some coding today, and it looks pretty slick. Does anyone know how much this costs in terms of performance/iterations?

The documentation didn’t offer much in terms of that.

Answer 1

• first, it iterates each element of the supplied collection
• then it iterates all elements of the list and compares the current element with them using .equals(..) (Note: this is about lists, as you specified in the question. Other collections behave differently)

So it’s O(n*m), where n and m are the sizes of both collections.

public boolean containsAll(Collection<?> c) {
    Iterator<?> e = c.iterator();
    while (e.hasNext())
        if (!contains(e.next()))
        return false;
    return true;
}