Java exit codes and meanings

There is no definition for what exit code 23 means. Exit codes have no convention on what the values represent other than that a nonzero status code indicates abnormal termination. Zero indicates success but even then it is completely dependent as to whether the developer adheres to this 'standard'.

In your Java application, when you call System.exit(n);, then the Java runtime environment will return n as the exit code back to the operating system.

What the number means depends on the program you are running - not Java itself, but the program you are running produces this number. There are no standard numbers. Look in the documentation of the program that produces this exit code to find out what it means.