为什么 AND(&) 运算符用于计算 Hashmap 中的最终索引 为什么不用 modulo(%) 运算符，即 hashValue & ()

Question

I am trying to understand HashMap implementation. I found after calculating key hash value, final hash value is generated using AND operator (hashValue & (n-1)) where n is size of bucket.Could someone explain why modulo is not used which will also guarantee output range within bucket size.

Answer 1

& runs faster, in exchange for working only for powers of two. (Specifically, x & (n - 1) == x % n if x is nonnegative and n is a power of two. x & (n - 1) also does what you want for a hash table -- even if x is negative, x & (n - 1) isn't -- unlike x % n .)

That's the complete and only reason.