java-hashmap

Capacity : 桶的size
threshold : 下次扩容的size阈值
loadFactor : 负载因子, 用于计算threshold .

loadFactor 负载因子越高, 扩容的阈值越高, 桶越少, hash冲突越大, 查询性能越低, 存储空间占用小.
loadFactor 负载因子越低，扩容的阈值越高，hash冲突少, 查询性能高, 存储空间占用大.

举例, 要总共插入16个元素,
开始：默认Capacity = 16, loadFactor =0.75, threshold = 16 * 0.75 = 12.

插入到12个元素, 检查loadFactor，开始扩容，resize：
Capacity = 32, loadFactor =0.75, threshold = 32 * 0.75 = 24.