public static final <E> Collection<Set<E>> of(Set<E> s) {

List<E> src = new ArrayList<>(s);

if (src.size() > 30) {

throw new IllegalArgumentException("Set too big " + s);

}

return new AbstractCollection<Set<E>>() {

@Override

public int size() {

return 1 << src.size();

}

@Override

public boolean contains(Object o) {

return o instanceof Set && src.containsAll((Set) o);

}

@Override

public Iterator<Set<E>> iterator() {

return new Iterator<Set<E>>() {

private int index = 0;

private int end = size();

@Override

public boolean hasNext() {

return index < end;

}

@Override

public Set<E> next() {

Set<E> result = new HashSet<>();

for (int i = 0, j = index; j != 0; i++, j >>= 1) {

if ((j & 1) == 1) {

result.add(src.get(i));

}

}

index++;

return result;

}

};

}

};

}

public static void main(String[] args) {

Set<Character> set = Set.of('a', 'b', 'c');

for (Set<Character> s : PowerSet.of(set)) {

System.out.println(s);

}

}