retainAll method
Implementation
void retainAll(Iterable<Object> elements) {
SplayTreeSet<E> retainSet = new SplayTreeSet<E>(_comparator, _validKey);
int modificationCount = _modificationCount;
for (Object object in elements) {
if (modificationCount != _modificationCount) {
throw new ConcurrentModificationError(this);
}
if (_validKey(object) && _splay(object) == 0) {
retainSet.add(_root.key);
}
}
if (retainSet._count != _count) {
_root = retainSet._root;
_count = retainSet._count;
_modificationCount++;
}
}