final Node[] resize() { Node[] oldTab = table; int oldCap = (oldTab == null) ? 0 : oldTab.length; int oldThr = threshold; int newCap, newThr = 0; if (oldCap > 0) { // 如果数组中元素超过设置的阈值 if (oldCap >= MAXIMUM_CAPACITY) { // 直接扩大到 MAX_VALUE threshold = Integer.MAX_VALUE; return oldTab; } // 预扩大，提前判断扩容的合理性 else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY && oldCap >= DEFAULT_INITIAL_CAPACITY) // 左移操作，相当于翻2倍 newThr = oldThr << 1; // double threshold } else if (oldThr > 0) // 如果旧的阈值大于0 newCap = oldThr; else { // 如果旧的阈值等于0 newCap = DEFAULT_INITIAL_CAPACITY; // 新的阈值是默认负载因子和默认初始容量的乘积 newThr = (int)(DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY); } // 如果新的阈值为0 if (newThr == 0) { float ft = (float)newCap * loadFactor; newThr = (newCap < MAXIMUM_CAPACITY && ft < (float)MAXIMUM_CAPACITY ? (int)ft : Integer.MAX_VALUE); } // 将新的阈值设为当前阈值 threshold = newThr; @SuppressWarnings({"rawtypes","unchecked"}) Node[] newTab = (Node[])new Node[newCap]; // 将新的桶数组设置为当前桶数组 table = newTab; if (oldTab != null) { // 遍历旧的桶数组 for (int j = 0; j < oldCap; ++j) { Node e; // 如果桶不为空 if ((e = oldTab[j]) != null) { oldTab[j] = null; // 如果桶只有一个键值对 if (e.next == null) // 计算新的索引位置，将键值对放入新的桶中 newTab[e.hash & (newCap - 1)] = e; // 如果是树中的节点 else if (e instanceof TreeNode) ((TreeNode)e).split(this, newTab, j, oldCap); else { // 如果桶有多个键值对 Node loHead = null, loTail = null; Node hiHead = null, hiTail = null; Node 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; // 将低位链表设置为新桶的头节点 newTab[j] = loHead; } if (hiTail != null) { hiTail.next = null; // 将高位链表设置为新桶的头节点 newTab[j + oldCap] = hiHead; } } } } } // 返回新的桶数组 return newTab; }