源码分析

/**
 * Initializes or doubles table size. If null, allocates in accord with initial
 * capacity target held in field threshold. Otherwise, because we are using
 * power-of-two expansion, the elements from each bin must either stay at same
 * index, or move with a power of two offset in the new table.
 * 初始化或加倍表大小。如果为空，则根据字段threshold中的initialcapacity目标进行分配。否则，因为      * 我们使用的是二次幂展开，所以每个bin中的元素要么保持在相同的下标，要么在新表中以二次幂偏移量移动。
 * @return the table
 */
final Node<K, V>[] resize() {
	Node<K, V>[] oldTab = table;//原table
	int oldCap = (oldTab == null) ? 0 : oldTab.length;//原容量
	int oldThr = threshold;//原阈值
	int newCap, newThr = 0;//新容量、新阈值
	if (oldCap > 0) {//原容量大于0
		if (oldCap >= MAXIMUM_CAPACITY) {//原容量大于等于最大容量
			threshold = Integer.MAX_VALUE;//Integer.MAX_VALUE作为阈值
			return oldTab;
		} else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY && oldCap >= DEFAULT_INITIAL_CAPACITY)//原容量的2倍小于最大容量，且原容量大于默认初始化容量
			newThr = oldThr << 1; //新阈值为原阈值的2倍（即原容量扩容，阈值也跟着扩容）
	} else if (oldThr > 0) // 原阈值大于0
		newCap = oldThr;//将原阈值作为新容量
	else { // 初始化容量为0，使用默认容量和默认阈值
		newCap = DEFAULT_INITIAL_CAPACITY;
		newThr = (int) (DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY);
	}
	if (newThr == 0) {//新阈值为0
		float ft = (float) newCap * loadFactor;//新容量乘以负载因子获得临时变量ft
		newThr = (newCap < MAXIMUM_CAPACITY && ft < (float) MAXIMUM_CAPACITY ? (int) ft : Integer.MAX_VALUE);//新容量小于最大容量并且临时变量ft也小于最大容量，将ft作为新阈值，否则将Integer.MAX_VALUE作为新阈值
	}
	threshold = newThr;//新阈值作为阈值
	@SuppressWarnings({ "rawtypes", "unchecked" })
	Node<K, V>[] newTab = (Node<K, V>[]) new Node[newCap];//根据新容量创建新数组
	table = newTab;//新数组作为HashMap的数组
	if (oldTab != null) {//以下为将原数组中的数据进行重新分配
		for (int j = 0; j < oldCap; ++j) {
			Node<K, V> e;
			if ((e = oldTab[j]) != null) {
				oldTab[j] = null;
				if (e.next == null)
					newTab[e.hash & (newCap - 1)] = e;
				else if (e instanceof TreeNode)
					((TreeNode<K, V>) e).split(this, newTab, j, oldCap);
				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;
					}
				}http://yezishuju.com/
			}
		}
	}
	return newTab;
}