Java Utililty Methods Set Intersect

if (a == null || b == null) {
    return Collections.EMPTY_SET;
Set<T> small = (a.size() > b.size()) ? b : a;
Set<T> big = (a.size() > b.size()) ? a : b;
Set<T> intersection = new HashSet<T>(small);
intersection.retainAll(big);
return intersection;
...

if (s1 == null || s2 == null)
    return new HashSet<T>();
Set<T> result = new HashSet<T>(s1);
result.retainAll(s2);
return result;

if (isEmpty(set1) || isEmpty(set2)) {
    return Collections.emptyList();
Set<T> intersection = new LinkedHashSet<T>();
for (T item : set1) {
    if (item != null && set2.contains(item)) {
        intersection.add(item);
return intersection;

if (isEmpty(firstSet)) {
    return secondSet == null ? new HashSet<T>(0) : secondSet;
if (isEmpty(secondSet)) {
    return firstSet;
firstSet.retainAll(secondSet);
return firstSet;
...

HashSet n = new HashSet(one.size());
Iterator it = one.iterator();
while (it.hasNext()) {
    Object v = it.next();
    if (two.contains(v)) {
        n.add(v);
return n;

Set<T> s = set();
intersect(set1, set2, s);
return s;

Set<E> intersect = new HashSet<>();
for (E entryA : a) {
    if (b.contains(entryA)) {
        intersect.add(entryA);
for (E entryB : b) {
    if (a.contains(entryB)) {
...

for (String s : a) {
    if (b.contains(s))
        return true;
return false;

List<T> mid = new LinkedList<T>(left);
mid.removeAll(right);
Set<T> result = new TreeSet<T>(left);
result.removeAll(mid);
return result;

Set<E> set = new HashSet<>(set1);
set.retainAll(set2);
return Collections.unmodifiableSet(set);