Question

I am looking at the implementation of HashMap in Java and am stuck at one point.

How is the indexFor function calculated?

static int indexFor(int h, int length) {
   return h & (length-1);
}

Thanks

Answer 1

It’s not calculating the hash, it’s calculating the bucket.

The expression h & (length-1) does a bit-wise AND on h using length-1, which is like a bit-mask, to return only the low-order bits of h, thereby making for a super-fast variant of h % length.