How do I use System.exit() in Java

Question

I've been learning Java for some months now and I came across this:

System.exit(int status);

I think you can use it to test your code depending on what "value" you give to it.

e.g if I want to check if a loop was used or worked as it should , I could do:

if(value == 1){
    System.out.println("Hi");
    System.exit(0);
}

But after a bit of testing it came out that I actually cant see the "value" after the loop executed.

Am I thinking of this right? Is there any other use of this code?

Related with System.exit() values: stackoverflow.com/questions/2434592/… — Egl
– Egl, Commented Jun 17, 2015 at 17:56
All processes in every common OS return an 'exit code' when they terminate. This code is usually 0 if the process was successful, or some other process-specific code if the process failed (exception thrown, invalid arguments, etc.). The value to the System.exit function is that code. — Colonel Thirty Two
– Colonel Thirty Two, Commented Jun 17, 2015 at 18:02
System.exit() shuts down the VM no matter if there are still threads running or how deeply nested the call stack is. Its the "get me out of here" call. The return code has no meaning to the VM itself - but its a simple and universally supported way of communicating that value to whatever environment started the VM. E.g. in a shell script, the script can act depending on the return code from the VM. — Durandal
– Durandal, Commented Jun 17, 2015 at 18:17

Mureinik · Accepted Answer · 2015-06-17 17:51:35Z

7

System.exit(value) terminates the JVM and uses value as the return value of the process. So, for instance, in *nix systems, you could use:

$ echo `java MyJavaClass`

answered Jun 17, 2015 at 17:51

Mureinik

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1 Comment

Bill Over a year ago

So i need echo to display (print) it's value? cause i am testing it in eclipse and no value is being printed.

GregH · Accepted Answer · 2015-06-17 17:52:22Z

2

The java.lang.System.exit() method terminates the currently running Java Virtual Machine.

The argument serves as a status code; by convention, a nonzero status code indicates abnormal termination.

Likewise, a 0 status code returns a normal termination;

System.exit(0) //exit signaling the process terminated successfully

System.exit(-1) //exit signaling the process did not terminate successfully

answered Jun 17, 2015 at 17:52

GregH

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Comments

Patricia Shanahan · Accepted Answer · 2015-06-17 18:26:00Z

1

To check the exit code in Eclipse, switch to the "Debug" view. For example, immediately after running:

public class Test {
  public static void main(String[] args) {
    System.exit(55);
  }
}

the top left window in the Debug view contains:

<terminated>Test [Java Application] 
    <terminated, exit value: 55>C:\Program Files\Java\jre1.8.0_31\bin\javaw.exe (Jun 17, 2015, 11:21:15 AM)

answered Jun 17, 2015 at 18:26

Patricia Shanahan

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Amir Afghani · Accepted Answer · 2015-06-17 17:52:43Z

0

System.exit(value)

will cause the program to terminate with the given value. Traditionally (on unix systems at least), 0 has been designated as the numeric value that will indicate successful execution of a program. All non-zero values indicate a failure mode that the calling environment will know how to interpret.

I think you can use it to test your code depending on what "value" you give to it.

I wouldn't use this methodology to test my code. Instead consider writing unit tests to test your code.

answered Jun 17, 2015 at 17:52

Amir Afghani

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user4668606 · Accepted Answer · 2015-06-17 17:51:55Z

-1

The documentation would (as usual) help a lot -.- . System.exit terminates the JVM.

answered Jun 17, 2015 at 17:51

user4668606

4 Comments

Bill Over a year ago

i couldnt figure it out thats why i asked, is that all it does ? cause i read that the value you use actually does something

user4668606 Over a year ago

@Bill as any other program, the return-value is 0, if the program was terminated on purpose, or some other value, if an error occured during runtime

Bill Over a year ago

yeah i got this but if i use this code in eclipse and run it no value will be printed , so all it does is to terminate the programm and all i need is a "break;" and this code (System.out()) is useless.

user4668606 Over a year ago

@Bill i guess the console will log something like "process terminated with exit-code ...". but unless you want to terminate the complete program, you shouldn't use System.exit

Colonel Thirty Two · Accepted Answer · 2015-06-17 18:00:54Z

-2

System.exit() Method can be use to terminate program so when you use this method it will terminate program as it reached to parameter value of System.exit() method.

edited Jun 17, 2015 at 18:00

Colonel Thirty Two

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answered Jun 17, 2015 at 17:59

Suresh Parmar

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