RunTime Complexity of ArrayList.contains function

Question

In java.util.ArrayList data structure, the function contains has time complexity of O(n) or O(1)?
I heard that java implement it in such way that it will be O(1) so if it true I'll be glad to know how it made like that.
thanks

Answer 1

I feel its highest possibility would be n but I think it just searches from start to finish. im sir you can look at the javadocs to find out!