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

private transient HashMap<E,Object> map;
//定義一個Object對象作為HashMap的value
private static final Object PRESENT = new Object();

    /**
     * Constructs a new, empty set; the backing <tt>HashMap</tt> instance has
     * default initial capacity (16) and load factor (0.75).
     */
    public HashSet() {
        map = new HashMap<>();
    }

public int size() {
        return map.size();
    }
public boolean isEmpty() {
        return map.isEmpty();
    }
public boolean contains(Object o) {
        return map.containsKey(o);
    }    
public boolean add(E e) {
        return map.put(e, PRESENT)==null;
	}
public V put(K key, V value) {
	    return putVal(hash(key), key, value, false, true);
	}
 /**
     * Returns an iterator over the elements in this set.  The elements
     * are returned in no particular order.
     *
     * @return an Iterator over the elements in this set
     * @see ConcurrentModificationException
     */
    public Iterator<E> iterator() {
        return map.keySet().iterator();
    }    

public Object clone() {
        try {
            HashSet<E> newSet = (HashSet<E>) super.clone();
            newSet.map = (HashMap<E, Object>) map.clone();
            return newSet;
        } catch (CloneNotSupportedException e) {
            throw new InternalError();
        }
    }

final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
               boolean evict) {
    Node<K,V>[] tab; Node<K,V> p; int n, i;
    //確認(rèn)初始化
    if ((tab = table) == null || (n = tab.length) == 0)
        n = (tab = resize()).length;
    //如果桶為空，直接插入新元素，也就是entry
    if ((p = tab[i = (n - 1) & hash]) == null)
        tab[i] = newNode(hash, key, value, null);
    else {
        Node<K,V> e; K k;
        //如果沖突，分為三種情況
        //key相等時讓舊entry等于新entry即可
        if (p.hash == hash &&
            ((k = p.key) == key || (key != null && key.equals(k))))
            e = p;
        //紅黑樹情況
        else if (p instanceof TreeNode)
            e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
        else {
            //如果key不相等，則連成鏈表
            for (int binCount = 0; ; ++binCount) {
                if ((e = p.next) == null) {
                    p.next = newNode(hash, key, value, null);
                    if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
                        treeifyBin(tab, hash);
                    break;
                }
                if (e.hash == hash &&
                    ((k = e.key) == key || (key != null && key.equals(k))))
                    break;
                p = e;
            }
        }
        if (e != null) { // existing mapping for key
            V oldValue = e.value;
            if (!onlyIfAbsent || oldValue == null)
                e.value = value;
            afterNodeAccess(e);
            return oldValue;
        }
    }
    ++modCount;
    if (++size > threshold)
        resize();
    afterNodeInsertion(evict);
    return null;
}

//Constructor - 1
public LinkedHashSet(int initialCapacity, float loadFactor)
{
      super(initialCapacity, loadFactor, true);              //Calling super class constructor
}
//Constructor - 2
public LinkedHashSet(int initialCapacity)
{
        super(initialCapacity, .75f, true);             //Calling super class constructor
}
//Constructor - 3
public LinkedHashSet()
{
        super(16, .75f, true);                //Calling super class constructor
}
//Constructor - 4
public LinkedHashSet(Collection<? extends E> c)
{
        super(Math.max(2*c.size(), 11), .75f, true);          //Calling super class constructor
        addAll(c);
}

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

//默認(rèn)構(gòu)造方法
public TreeSet() {
    this(new TreeMap<E,Object>());
}
//構(gòu)造包含指定 collection 元素的新 TreeSet，按照其元素的自然順序進行排序。
public TreeSet(Comparator<? super E> comparator) {
        this(new TreeMap<>(comparator));
}
//構(gòu)造新的空 TreeSet，根據(jù)指定比較器進行排序。
public TreeSet(Collection<? extends E> c) {
    this();
    addAll(c);
}
//構(gòu)造與指定有序 set 具有相同映射關(guān)系和相同排序的新 TreeSet
public TreeSet(SortedSet<E> s) {
    this(s.comparator());
    addAll(s);
}
TreeSet(NavigableMap<E,Object> m) {
    this.m = m;
}

public boolean add(E e) {
        return m.put(e, PRESENT)==null;
    }
public V put(K key, V value) {
    Entry<K,V> t = root;
    if (t == null) {
    //空樹時，判斷節(jié)點是否為空
        compare(key, key); // type (and possibly null) check
        root = new Entry<>(key, value, null);
        size = 1;
        modCount++;
        return null;
    }
    int cmp;
    Entry<K,V> parent;
    // split comparator and comparable paths
    Comparator<? super K> cpr = comparator;
    //非空樹，根據(jù)傳入比較器進行節(jié)點的插入位置查找
    if (cpr != null) {
        do {
            parent = t;
            //節(jié)點比根節(jié)點小，則找左子樹，否則找右子樹
            cmp = cpr.compare(key, t.key);
            if (cmp < 0)
                t = t.left;
            else if (cmp > 0)
                t = t.right;
                //如果key的比較返回值相等，直接更新值（一般compareto相等時equals方法也相等）
            else
                return t.setValue(value);
        } while (t != null);
    }
    else {
    //如果沒有傳入比較器，則按照自然排序
        if (key == null)
            throw new NullPointerException();
        @SuppressWarnings("unchecked")
            Comparable<? super K> k = (Comparable<? super K>) key;
        do {
            parent = t;
            cmp = k.compareTo(t.key);
            if (cmp < 0)
                t = t.left;
            else if (cmp > 0)
                t = t.right;
            else
                return t.setValue(value);
        } while (t != null);
    }
    //查找的節(jié)點為空，直接插入，默認(rèn)為紅節(jié)點
    Entry<K,V> e = new Entry<>(key, value, parent);
    if (cmp < 0)
        parent.left = e;
    else
        parent.right = e;
        //插入后進行紅黑樹調(diào)整
    fixAfterInsertion(e);
    size++;
    modCount++;
    return null;
}    

public V get(Object key) {
    Entry<K,V> p = getEntry(key);
    return (p==null ? null : p.value);
}