static final int TREEIFY_THRESHOLD = 8;

public V put(K key, V value) {
        return putVal(hash(key), key, value, false, true);
 }
 
 
final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
                   boolean evict) {
        Node<K,V>[] tab;
    Node<K,V> p;
    int n, i;
    //如果當前map中無資料，執行resize方法。並且返回n
        if ((tab = table) == null || (n = tab.length) == 0)
            n = (tab = resize()).length;
     //如果要插入的鍵值對要存放的這個位置剛好沒有元素，那麼把他封裝成Node物件，放在這個位置上即可
        if ((p = tab[i = (n - 1) & hash]) == null)
            tab[i] = newNode(hash, key, value, null);
    //否則的話，說明這上面有元素
        else {
            Node<K,V> e; K k;
        //如果這個元素的key與要插入的一樣，那麼就替換一下。
            if (p.hash == hash &&
                ((k = p.key) == key || (key != null && key.equals(k))))
                e = p;
        //1.如果當前節點是TreeNode型別的資料，執行putTreeVal方法
            else if (p instanceof TreeNode)
                e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
            else {
        //還是遍歷這條鏈子上的資料，跟jdk7沒什麼區別
                for (int binCount = 0; ; ++binCount) {
                    if ((e = p.next) == null) {
                        p.next = newNode(hash, key, value, null);
            //2.完成了操作後多做了一件事情，判斷，並且可能執行treeifyBin方法
                        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) //true || --
                    e.value = value;
           //3.
                afterNodeAccess(e);
                return oldValue;
            }
        }
        ++modCount;
    //判斷閾值，決定是否擴容
        if (++size > threshold)
            resize();
        //4.
        afterNodeInsertion(evict);
        return null;
    }