How Best to Compare Two Collections in Java and Act on Them?

Question

I have two collections of the same object, Collection oldSet and Collection newSet. The required logic is as follow:

Answer 1

public static boolean doCollectionsContainSameElements(
        Collection c1, Collection c2){

    if (c1 == null || c2 == null) {
        return false;
    }
    else if (c1.size() != c2.size()) {
        return false;
    } else {    
        return c1.containsAll(c2) && c2.containsAll(c1);
    }       
}