What does this code exactly mean? What does the 0 stand for?

Question

System.exit(0);

Answer 1

It terminates the currently running Java Virtual Machine.The argument serves as a status code, by convention, a nonzero status code indicates abnormal termination. This will stop the jvm normally :D

Answer 2

It exits your program, and 0 is the exit code. 0 means it went fine, whereas other values indicate that it didn't.