Why ArrayList grows at a rate of 1.5, but for Hashmap it's 2?

Question

As per Sun Java Implementation, during expansion, ArrayList grows to 3/2 it\'s initial capacity whereas for HashMap the expansion rate is double. What is reason behind this?

Answer 1

The way HashMap is designed/implemented its underlying number of buckets must be a power of 2 (even if you give it a different size, it makes it a power of 2), thus it grows by a factor of two each time. An ArrayList can be any size and it can be more conservative in how it grows.