Hashtable 负载因子Load Factor

负载因子(load factor)，它用来衡量哈希表的 空/满 程度，一定程度上也可以体现查询的效率，计算公式为:

The ratio of the number of elements in the hash table to the table size is
called the load factor. Studies have shown that hash table performance is best
when the load factor is 1.0, or when the table size exactly equals the number
of elements.

public Hashtable(int capacity, float loadFactor);

负载因子 = 总键值对数 / 箱子个数