Why is vector array doubled?

Question

Why does the classic implementation of Vector (ArrayList for Java people) double its internal array size on each expansion instead of tripling or quadrupling it?

Answer 1

Any multiple is a compromise. Make it too big and you waste too much memory. Make it too small and you waste much time for reallocations and copying. I guess that doubling is there because it works and is very easy to implement. I also saw a proprietary STL-like library that uses 1.5 as multiplier for the same - I guess its developers considered doubling wasting too much memory.