HashMap紅黑樹轉換條件是什麼？

以下為HashMap的put方法

    final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
                   boolean evict) {
        Node<K,V>[] tab; Node<K,V> p; int n, i;
        if ((tab = table) == null || (n = tab.length) == 0)
            n = (tab = resize()).length;
        if ((p = tab[i = (n - 1) & hash]) == null)
            tab[i] = newNode(hash, key, value, null);
        else {
            Node<K,V> e; K k;
            if (p.hash == hash &&
                ((k = p.key) == key || (key != null && key.equals(k))))
                e = p;
            // 這裡判斷節點是否已經轉化為紅黑樹節點
            else if (p instanceof TreeNode)
                e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
            else {
                for (int binCount = 0; ; ++binCount) {
                    // 判斷下一節點是否為空
                    if ((e = p.next) == null) {
                        // 如果是則將下個節點置為當前節點
                        p.next = newNode(hash, key, value, null);
                        // TREEIFY_THRESHOLD=8
                        // 條件一：  判斷如果當前bucket的位置連結串列長度是否大於8
                        if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
                            // 嘗試轉化紅黑樹
                            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;
    }
 

• 以上方法可以看見，若put完節點後，當前連結串列長度達到8則開始嘗試執行treeifyBin方法來轉化紅黑樹。接下來我們看下treeifyBin方法做了什麼

    final void treeifyBin(Node<K,V>[] tab, int hash) {
        int n, index; Node<K,V> e;
        // MIN_TREEIFY_CAPACITY=64
        // 條件二： 判斷當前陣列長度是否大於64，若不大於則進行resize操作
        if (tab == null || (n = tab.length) < MIN_TREEIFY_CAPACITY)
            resize();
        else if ((e = tab[index = (n - 1) & hash]) != null) {
            // 若滿足條件一二，則轉化為紅黑樹結構
            TreeNode<K,V> hd = null, tl = null;
            do {
                // 將所有節點都轉化為TreeNode
                TreeNode<K,V> p = replacementTreeNode(e, null);
                if (tl == null)
                    hd = p;
                else {
                    p.prev = tl;
                    tl.next = p;
                }
                tl = p;
            } while ((e = e.next) != null);
            if ((tab[index] = hd) != null)
                // 轉化為紅黑樹
                hd.treeify(tab);
        }
    }
 

後續看到此部落格，寫的更詳細：https://www.cnblogs.com/wangflower/p/12235595.html