How to find which element has been removed in an array?

Question

Java

It's a simple problem, but one I couldn't answer. There is an array of ints or bytes, we delete some element in it by forming a new array without this element. The arrays are unsorted. How, given these 2 arrays, to find out which element was removed? Naturally, without enumeration, the most effective / quick solution is needed.
The task is common, but if we take the context of the language, then we take java. Maybe there are some standard methods that I did not know about.

Answer 1

Half division. O(logN)

Answer 2

At the time of formation, remember the value or index of the deleted element