Java. How to fix ConcurrentModificationException in this code?

Question

Java

This code throws java.util.ConcurrentModificationException when creating a large number of threads. And in the 84th line, sometimes there is an output beyond the aisles of the array (-1). If it's not difficult, write what's wrong in the code...
https://github.com/Drunya2/BattleShip/blob/master/...

Answer 1

At a minimum, using a non-thread-safe ArrayList is not correct when multithreading, which is why you get the ConcurrentModificationException. Here is a nice overview of Concurrent Collections