'java.util.AbstractSet#removeAll'
method determines which is the smaller of this set and the
specified collection, by invoking the size method on each. If this set has fewer elements, then the implementation iterates over
this set, checking each element returned by the iterator in turn to see if it is contained in the specified collection. If it is
so contained, it is removed from this set with the iterator's remove method. If the specified collection has fewer elements, then
the implementation iterates over the specified collection, removing from this set each element returned by the iterator, using this
set's remove method.
It means that if the collection to remove is of equal or larger size than the set, then the implementation of the
'java.util.List#contains'
method is called, which in many implementations they will perform costly linear
searches.
New in 2020.3