// newCapacity為新的容量
void resize(int newCapacity) {
    // 小數(shù)組，臨時(shí)過(guò)度下
    Entry[] oldTable = table;
    // 擴(kuò)容前的容量
    int oldCapacity = oldTable.length;
    // MAXIMUM_CAPACITY 為最大容量，2 的 30 次方 = 1<<30
    if (oldCapacity == MAXIMUM_CAPACITY) {
        // 容量調(diào)整為 Integer 的最大值 0x7fffffff（十六進(jìn)制）=2 的 31 次方-1
        threshold = Integer.MAX_VALUE;
        return;
    }

    // 初始化一個(gè)新的數(shù)組（大容量）
    Entry[] newTable = new Entry[newCapacity];
    // 把小數(shù)組的元素轉(zhuǎn)移到大數(shù)組中
    transfer(newTable, initHashSeedAsNeeded(newCapacity));
    // 引用新的大數(shù)組
    table = newTable;
    // 重新計(jì)算閾值
    threshold = (int)Math.min(newCapacity * loadFactor, MAXIMUM_CAPACITY + 1);
}

void transfer(Entry[] newTable, boolean rehash) {
    // 新的容量
    int newCapacity = newTable.length;
    // 遍歷小數(shù)組
    for (Entry<K,V> e : table) {
        while(null != e) {
            // 拉鏈法，相同 key 上的不同值
            Entry<K,V> next = e.next;
            // 是否需要重新計(jì)算 hash
            if (rehash) {
                e.hash = null == e.key ? 0 : hash(e.key);
            }
            // 根據(jù)大數(shù)組的容量，和鍵的 hash 計(jì)算元素在數(shù)組中的下標(biāo)
            int i = indexFor(e.hash, newCapacity);

            // 同一位置上的新元素被放在鏈表的頭部
            e.next = newTable[i];

            // 放在新的數(shù)組上
            newTable[i] = e;

            // 鏈表上的下一個(gè)元素
            e = next;
        }
    }
}

final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
               boolean evict) {
    Node<K,V>[] tab; Node<K,V> p; int n, i;

    // 步驟①：tab為空則創(chuàng)建
    if ((tab = table) == null || (n = tab.length) == 0)
        n = (tab = resize()).length;

    // 步驟②：計(jì)算index，并對(duì)null做處理 
    if ((p = tab[i = (n - 1) & hash]) == null)
        tab[i] = newNode(hash, key, value, null);
    else {
        Node<K,V> e; K k;

        // 步驟③：節(jié)點(diǎn)key存在，直接覆蓋value
        if (p.hash == hash &&
            ((k = p.key) == key || (key != null && key.equals(k))))
            e = p;

        // 步驟④：判斷該鏈為紅黑樹
        else if (p instanceof TreeNode)
            e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);

        // 步驟⑤：該鏈為鏈表
        else {
            for (int binCount = 0; ; ++binCount) {
                if ((e = p.next) == null) {
                    p.next = newNode(hash, key, value, null);

                    //鏈表長(zhǎng)度大于8轉(zhuǎn)換為紅黑樹進(jìn)行處理
                    if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
                        treeifyBin(tab, hash);
                    break;
                }

                // key已經(jīng)存在直接覆蓋value
                if (e.hash == hash &&
                    ((k = e.key) == key || (key != null && key.equals(k))))
                    break;
                p = e;
            }
        }

        // 步驟⑥、直接覆蓋
        if (e != null) { // existing mapping for key
            V oldValue = e.value;
            if (!onlyIfAbsent || oldValue == null)
                e.value = value;
            afterNodeAccess(e);
            return oldValue;
        }
    }
    ++modCount;

    // 步驟⑦：超過(guò)最大容量 就擴(kuò)容
    if (++size > threshold)
        resize();
    afterNodeInsertion(evict);
    return null;
}

if ((p = tab[i = (n - 1) & hash]) == null)
    tab[i] = newNode(hash, key, value, null);

final Node<K,V>[] resize() {
    Node<K,V>[] oldTab = table;
    int oldCap = (oldTab == null) ? 0 : oldTab.length;
    int oldThr = threshold;
    int newCap, newThr = 0;
    if (oldCap > 0) {
        // 超過(guò)最大值就不再擴(kuò)充了，就只好隨你碰撞去吧
        if (oldCap >= MAXIMUM_CAPACITY) {
            threshold = Integer.MAX_VALUE;
            return oldTab;
        }
        // 沒(méi)超過(guò)最大值，就擴(kuò)充為原來(lái)的2倍
        else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY &&
                 oldCap >= DEFAULT_INITIAL_CAPACITY)
            newThr = oldThr << 1; // double threshold
    }
    else if (oldThr > 0) // initial capacity was placed in threshold
        newCap = oldThr;
    else {               // zero initial threshold signifies using defaults
        newCap = DEFAULT_INITIAL_CAPACITY;
        newThr = (int)(DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY);
    }
    // 計(jì)算新的resize上限
    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"})
        Node<K,V>[] newTab = (Node<K,V>[])new Node[newCap];
    table = newTab;
}