Why does java.util.Arrays.sort(Object[]) use 2 kinds of sorting algorithms?

Question

I found that java.util.Arrays.sort(Object[]) use 2 kinds of sorting algorithms(in JDK 1.6).

pseudocode:

if(array.length<7)
   inserti         


        

Answer 1

Quoted from: http://en.wikipedia.org/wiki/Insertion_sort

Some divide-and-conquer algorithms such as quicksort and mergesort sort by 
recursively dividing the list into smaller sublists which are then sorted. 
A useful optimization in practice for these algorithms is to use insertion 
sort for sorting small sublists, where insertion sort outperforms these more 
complex algorithms. The size of list for which insertion sort has the advantage 
varies by environment and implementation, but is typically between eight and 
twenty elements.