you can get the size of the arrayList trivially (.size())

check this size is > 0

for (int i = arraySize - 50 ; i < arraySize ; i++) {
  arrayName.get(i).doWhatever();
}

@koogy if size >=0 and <50 then your solution will crash because i will start as a negative number in the loop

Try this modification

for (int i = max(arrayName.size() - 50, 0) ; i < arrayName.size(); i++) {
  arrayName.get(i).doWhatever();
}

yeah, you're right. my check is wrong. i should've been vaguer 8)

I tried your suggestions, and it gives me the results I wanted! Many thanks!