Although looping through the list twice is one way of doing it, the faster way of doing it is to only loop once (or just use Collections.reverse)
Try it with one loop, it's much easier to read and performs better (your double loop is probably overwriting values in the backward array):
for (int i = 0; i < arraysize; i++){
backward[arraysize-i-1] = arr[i];
}
(Wrote the above on my phone, so apologies for any potential errors)