You are so careful... This means you can teach yourself.
System.exit(0) means that application ends normally.
System.exit(1) means that application ends
becaue of error.
Java appication is just one process on your machine. Your system may monitor and catch the status of your Java application. In Unix system, there are various error levels...
1, 2, 3,,.. The system can judge what happened with your application by catching these number.
However, if we just do small exercises, these numbers do not matter because we do not catch them.