jdk1.8 hashset源码

public class <E>
   	extends AbstractSet<E>
   	implements Set<E>, Cloneable, java.io.Serializable

private transient HashMap<E,Object> map;

public () {
       map = new HashMap<>();
   }

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

   public (int initialCapacity, float loadFactor) {
       map = new HashMap<>(initialCapacity, loadFactor);
   }

   public (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;
   }