HashSet源码解析

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 contains(Object o) {
    return map.containsKey(o);
}
public boolean add(E e) {
    return map.put(e, PRESENT) == null;
}
public boolean remove(Object o) {
    return map.remove(o) == PRESENT;
}
public void clear() {
    map.clear();
}
public int size() {
    return map.size();
}
public boolean isEmpty() {
    return map.isEmpty();
}
public Iterator<E> iterator() {
    return map.keySet().iterator();
}