HashMap- resize()

    final Node<K,V>[] resize() {
        Node<K,V>[] oldTab = table;
        int oldCap = (oldTab == null) ? 0 : oldTab.length;
        int oldThr = threshold;
        int newCap, newThr = 0;
        //扩容的时候会用到，因为只有在有初始值的时候oldcap才能大于0
        if (oldCap > 0) {
        //oldCap达到了最大值，那么就等于最大值
            if (oldCap >= MAXIMUM_CAPACITY) {
                threshHold也等于最大值
                threshold = Integer.MAX_VALUE;
                return oldTab;
            }
            //如果oldCap移位后小于最大值，就给阈值也左移一位
            else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY &&
                     oldCap >= DEFAULT_INITIAL_CAPACITY)
                newThr = oldThr << 1; // double threshold
        }
        //初始化，有参数
        else if (oldThr > 0) // initial capacity was placed in threshold
            newCap = oldThr;
        //初始化，没有参数
        else {               // zero initial threshold signifies using defaults
            newCap = DEFAULT_INITIAL_CAPACITY;
            newThr = (int)(DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY);
        }
        //有参数初始化，给阈值赋值
        if (newThr == 0) {
            float ft = (float)newCap * loadFactor;
            newThr = (newCap < MAXIMUM_CAPACITY && ft < (float)MAXIMUM_CAPACITY ?
                      (int)ft : Integer.MAX_VALUE);
        }
        threshold = newThr;
        @SuppressWarnings({"rawtypes","unchecked"})
        //创建新的table
            Node<K,V>[] newTab = (Node<K,V>[])new Node[newCap];
        table = newTab;
        
        
        //如果不是初始化就做数据搬迁
        if (oldTab != null) {
        //对table遍历
            for (int j = 0; j < oldCap; ++j) {
                Node<K,V> e;
                //如果数组里面没有值，j
                if ((e = oldTab[j]) != null) {
                    oldTab[j] = null;
                    //table的里的值为空，就给赋值
                    if (e.next == null)
                        newTab[e.hash & (newCap - 1)] = e;
                    //如果式红黑树，就新搬迁数据
                    else if (e instanceof TreeNode)
                        ((TreeNode<K,V>)e).split(this, newTab, j, oldCap);
                    //如果式链表，就做数据搬迁
                    else { // preserve order
                        Node<K,V> loHead = null, loTail = null;
                        Node<K,V> hiHead = null, hiTail = null;
                        Node<K,V> next;
                        do {
                            next = e.next;
                            if ((e.hash & oldCap) == 0) {
                                if (loTail == null)
                                    loHead = e;
                                else
                                    loTail.next = e;
                                loTail = e;
                            }
                            else {
                                if (hiTail == null)
                                    hiHead = e;
                                else
                                    hiTail.next = e;
                                hiTail = e;
                            }
                        } while ((e = next) != null);
                        if (loTail != null) {
                            loTail.next = null;
                            newTab[j] = loHead;
                        }
                        if (hiTail != null) {
                            hiTail.next = null;
                            newTab[j + oldCap] = hiHead;
                        }
                    }
                }
            }
        }
        return newTab;
    }