CODEWITHSUNDEEP
javaexit-code
bane
bane

Reputation: 831

Why do we have exit codes in Java?

In Java, we use System.exit(int) to exit the program. The reason for an "exit value" in C was that the exit value was used to check for errors in a program. But in Java, errors are reflected by an Exception being thrown, thus they can be handled easily. So why do we have exit values in Java at all?

Upvotes: 6

Views: 10509

Answers (4)

Dev
Dev

Reputation: 146

Long story short, Exit codes are simplified signals to the user who encounters an exception while running a Java program. Since we assume that most of the users do not understand stack trace data of an exception, these simple non zero custom code will tell them that something is wrong and this should be reported to the vendor. So the vendor gets the code and he knows the stack trace associated with that code and tries to repair the system. This is an abstraction provided by the programmers so that users don't have to read and report voluminous stack traces. A very good analogy here is the getErrorCode() method in SQLException class. This method also closes the current JVM that is running on the client machine. This implies that this terminates all the threads that are in the JVM. This method calls the exit method in the class Java.lang.Runtime. If you go to the documentation of this method, you will understand how virtual machine is shut down.

This is the link http://docs.oracle.com/javase/6/docs/api/java/lang/Runtime.html#exit%28int%29

Upvotes: 0

asteri
asteri

Reputation: 11572

For the same reason.

Exit codes are exclusively used by parties and applications outside of the program for debugging and handling purposes. A super-application can definitely handle a return code better than trying to parse a stack trace.

Also, if you are creating an application for an end-user, you would much rather exit gracefully from your app than post a bunch of stack trace information, for a couple of reasons: one, you will just be scaring them with lots of crazy-looking techno-gibberish, and two, stack traces often reveal sensitive and confidential information about the way the program is structured fundamentally (giving a potential attacker more knowledge about the system).

For a real-world example, I was working on a Java Batch program which used exit codes for its jobs. A user could see whether the job executed successfully or not based on whether the exit code was "0". If it was anything else, they could contact technical support, armed with the additional information of the exit code, and the help desk would have all the necessary information based on that exit code to help them out. It works much nicer than trying to ask a non-technical end-user, "Okay, so what Exception are you getting?"

Upvotes: 3

Rahul
Rahul

Reputation: 16335

exit values are returned to the callers to signal the successful or insuccessful completion of the program. The caller may not be able to catch the exception and handle it accordingly.

For eg. 0 exit value means successful completion whereas non-zero return value means some error in execution.

Also, System.exit() will make all the threads in the application to stop at that point itself.

Upvotes: 0

Peter Lawrey
Peter Lawrey

Reputation: 533520

exit values are returned to the calling program e.g. the shell. An Exception cannot be caught by an external program.

BTW When you throw an Exception it is caught by that thread or that thread dies, the finally blocks are still called for that thread. When you call System.exit(), all threads stop immediately and finally blocks are not called.

Upvotes: 14

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