Java HashSet

public HashSet() {
        map = new HashMap<>();
    }
 
 public HashSet(Collection<? extends E> c) {
        map = new HashMap<>(Math.max((int) (c.size()/.75f) + 1, 16));
        addAll(c);
    }
public HashSet(int initialCapacity, float loadFactor) {
        map = new HashMap<>(initialCapacity, loadFactor);
    }
public HashSet(int initialCapacity) {
        map = new HashMap<>(initialCapacity);
    }
HashSet(int initialCapacity, float loadFactor, boolean dummy) {
        map = new LinkedHashMap<>(initialCapacity, loadFactor);
    }

public boolean add(E e) {
        return map.put(e, PRESENT)==null;
    }