time complexity or hidden cost of .length in java

Question

I was looking at a project in java and found a for loop which was written like below:

for(int i=1; i

        

Answer 1

in java arrays are fixed. Once you declare it you can not change that array's size in memory (if you tried to change the array size it will make a new array in memory).

Because of this we get O(1) length lookup. As we know the total size in memory of the array. If we also look up the size in memory of the first index we can do a quick calculation to get length at O(1) speed. As no matter how big our array is, its going take the same amount of time to lookup the size in memory and lookup the first index's size