2.     /**
    3.      * Moves and/or copies the nodes in each bin to new table. See
    4.      * above for explanation.
    5.      */
    6.     private final void transfer(Node<K,V>[] tab, Node<K,V>[] nextTab) {//tab 原数组 nextTab 新数组
    7.         int n = tab.length, stride;
    8.         if ((stride = (NCPU > 1) ? (n >>> 3) / NCPU : n) < MIN_TRANSFER_STRIDE)
    9.             stride = MIN_TRANSFER_STRIDE; // subdivide range
    10.         if (nextTab == null) {            // initiating 如果新数组为空，则初始化新数组
    11.             try {
    12.                 @SuppressWarnings("unchecked")
    13.                 Node<K,V>[] nt = (Node<K,V>[])new Node<?,?>[n << 1];//容量乘以2
    14.                 nextTab = nt;
    15.             } catch (Throwable ex) {      // try to cope with OOME
    16.                 sizeCtl = Integer.MAX_VALUE;
    17.                 return;
    18.             }
    19.             nextTable = nextTab;
    20.             transferIndex = n;
    21.         }
    22.         int nextn = nextTab.length;
    23.         ForwardingNode<K,V> fwd = new ForwardingNode<K,V>(nextTab);
    24.         boolean advance = true;
    25.         boolean finishing = false; // to ensure sweep before committing nextTab
    26.         for (int i = 0, bound = 0;;) { //开始搬迁
    27.             Node<K,V> f; int fh;
    28.             while (advance) {
    29.                 int nextIndex, nextBound;
    30.                 if (--i >= bound || finishing)
    31.                     advance = false;
    32.                 else if ((nextIndex = transferIndex) <= 0) {
    33.                     i = -1;
    34.                     advance = false;
    35.                 }
    36.                 else if (U.compareAndSwapInt
    37.                          (this, TRANSFERINDEX, nextIndex,
    38.                           nextBound = (nextIndex > stride ?
    39.                                        nextIndex - stride : 0))) {
    40.                     bound = nextBound;
    41.                     i = nextIndex - 1;
    42.                     advance = false;
    43.                 }
    44.             }
    45.             if (i < 0 || i >= n || i + n >= nextn) {
    46.                 int sc;
    47.                 if (finishing) {
    48.                     nextTable = null;
    49.                     table = nextTab;
    50.                     sizeCtl = (n << 1) - (n >>> 1);
    51.                     return;
    52.                 }
    53.                 if (U.compareAndSwapInt(this, SIZECTL, sc = sizeCtl, sc - 1)) {
    54.                     if ((sc - 2) != resizeStamp(n) << RESIZE_STAMP_SHIFT)
    55.                         return;
    56.                     finishing = advance = true;
    57.                     i = n; // recheck before commit
    58.                 }
    59.             }
    60.             else if ((f = tabAt(tab, i)) == null)
    61.                 //如果已经处理完了，就会把链表头替换为fwd(相当于一个标志位，表示处理完了)
    62.                 advance = casTabAt(tab, i, null, fwd);
    63.             else if ((fh = f.hash) == MOVED)
    64.                 //如果已经是fwd (MOVED) 了，则进入下一轮循环
    65.                 advance = true; // already processed
    66.             else {
    67.                 synchronized (f) {
    68.                     if (tabAt(tab, i) == f) {
    69.                         Node<K,V> ln, hn;
    70.                         if (fh >= 0) {
    71.                             // >= 0 表示为普通节点
    72.                             int runBit = fh & n;
    73.                             Node<K,V> lastRun = f;
    74.                             for (Node<K,V> p = f.next; p != null; p = p.next) {
    75.                                 int b = p.hash & n;
    76.                                 if (b != runBit) {
    77.                                     runBit = b;
    78.                                     lastRun = p;
    79.                                 }
    80.                             }
    81.                             if (runBit == 0) {
    82.                                 ln = lastRun;
    83.                                 hn = null;
    84.                             }
    85.                             else {
    86.                                 hn = lastRun;
    87.                                 ln = null;
    88.                             }
    89.                             for (Node<K,V> p = f; p != lastRun; p = p.next) {
    90.                                 int ph = p.hash; K pk = p.key; V pv = p.val;
    91.                                 if ((ph & n) == 0)
    92.                                     ln = new Node<K,V>(ph, pk, pv, ln);
    93.                                 else
    94.                                     hn = new Node<K,V>(ph, pk, pv, hn);
    95.                             }
    96.                             setTabAt(nextTab, i, ln);
    97.                             setTabAt(nextTab, i + n, hn);
    98.                             setTabAt(tab, i, fwd);
    99.                             advance = true;
    100.                         }
    101.                         else if (f instanceof TreeBin) {
    102.                             // 为负数(<=-2)，表示树节点
    103.                             TreeBin<K,V> t = (TreeBin<K,V>)f;
    104.                             TreeNode<K,V> lo = null, loTail = null;
    105.                             TreeNode<K,V> hi = null, hiTail = null;
    106.                             int lc = 0, hc = 0;
    107.                             for (Node<K,V> e = t.first; e != null; e = e.next) {
    108.                                 int h = e.hash;
    109.                                 TreeNode<K,V> p = new TreeNode<K,V>
    110.                                     (h, e.key, e.val, null, null);
    111.                                 if ((h & n) == 0) {
    112.                                     if ((p.prev = loTail) == null)
    113.                                         lo = p;
    114.                                     else
    115.                                         loTail.next = p;
    116.                                     loTail = p;
    117.                                     ++lc;
    118.                                 }
    119.                                 else {
    120.                                     if ((p.prev = hiTail) == null)
    121.                                         hi = p;
    122.                                     else
    123.                                         hiTail.next = p;
    124.                                     hiTail = p;
    125.                                     ++hc;
    126.                                 }
    127.                             }
    128.                             ln = (lc <= UNTREEIFY_THRESHOLD) ? untreeify(lo) :
    129.                                 (hc != 0) ? new TreeBin<K,V>(lo) : t;
    130.                             hn = (hc <= UNTREEIFY_THRESHOLD) ? untreeify(hi) :
    131.                                 (lc != 0) ? new TreeBin<K,V>(hi) : t;
    132.                             setTabAt(nextTab, i, ln);
    133.                             setTabAt(nextTab, i + n, hn);
    134.                             setTabAt(tab, i, fwd);
    135.                             advance = true;
    136.                         }
    137.                     }
    138.                 }
    139.             }
    140.         }
    141.     }