Why does Java 6 Arrays#sort(Object[]) change from mergesort to insertionsort for small arrays?

Question

Java 6\'s mergesort implementation in Arrays.java uses an insertion-sort if the array length is less than some threshold. This value is hard-coded to 7. As th

Answer 1

Insertion sort is n(n-1)/2 and merge sort is n*(log n with base 2 ).

Considering this -

1. For Array of Length 5 => Insetion sort = 10 and merge sort is 11.609
2. For Array of Length 6 => Insetion sort = 15 and merge sort is 15.509
3. For Array of Length 7 => Insetion sort = 21 and merge sort is 19.651
4. For Array of Length 8 => Insetion sort = 28 and merge sort is 24

From above data it is clear, till length 6, insetion sort is faster and after 7, merge sort is efficient.

That explains why 7 is used.