Length of an array is a public final int, so no calculation is done.

see here

http://docs.oracle.com/javase/specs/jls/se7/html/jls-10.html#jls-10.7

That is not true.

i<length

and

i<arr.length

have exactly the same cost.

The difference would be, when comparing to collection size, such as ArrayList and using .size() method, but here it doesn't matter.