I got curious with System.exit(0) so I put (1) to see what happens but didn't see any difference between a 0 or 1.

Exit terminates a process, in this case the java program you are running. 0 shows successful termination and any number other than 0 indicates faulty termination. You might not be able to see much but when you run a software and it throws an error code... ex. error 984, that often happens which the use of such exit function that returns a certain exit code which helps indicate a specific error and terminates the process. So basically the 0, 1 etc you placed in that exit method, is returned to the operating system to indicate if it was terminated successfully or not, that's why you don't see much of a difference.