In this article we want to explain the Java System.exit method in Java.
1. Syntax and functionality of the Java System.exit
The java.lang.System.exit() method exits current program by terminating running Java virtual machine. This method takes a status code as an argument. Following is the syntax for java.lang.System.exit() method:
public static void exit(int status)
1.1 Parameters
status − This is the exit status.
exit(0) : means a normal exit.
exit(1) or exit(-1) or any other non-zero value – means an abnormal exit.
Now lets see Example01 to understand it better:
Exit class
public class Exit {
public static void main(String[] args)
{
String arr[] = {"It", "is", "time", "to", "exit"};
for (int i = 0; i < arr.length; i++)
{
if (arr[i].equalsIgnoreCase("exit"))
{
System.out.println("exit...");
// Terminate JVM
System.exit(0);
}
else
System.out.println(arr[i] + " ");
}
System.out.println("End of Program");
}
}
Output is:
It is time to exit...
When we call the System.exit the subsequent code after the System.exit is effectively unreachableand yet, the compiler does not know about it.
System.exit(0);
System.out.println("This line is unreachable");It’s not a good idea to shut down a program with System.exit(0). Because it gives us the same result of exiting from the main method and also stops the subsequent lines from executing, also the thread invoking System.exit blocks until the JVM terminates. If a shutdown hook submits a task to this thread, it leads to a deadlock.
2. When to use System.exit() ?
Actually when there is an abnormal condition and we need to exit the program immediately.
Also, if we have to terminate the program from a place other than the main method, System.exit is one way of achieving it.
Also a script can rely on the exit codes of commands it invokes. For example, instead of throwing an exception, we can return an abnormal exit code that can then be interpreted by the calling script.
Now lets see Example02:
ReadFile class
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
public class ReadFile {
public static void main(String[] args) {
try {
BufferedReader br = new BufferedReader(new FileReader("myFile.txt"));
System.out.println(br.readLine());
br.close();
} catch (IOException e) {
System.out.println("Exiting using System.exit()");
System.exit(-1);
} finally {
System.out.println("Exiting the program");
}
}
}
Output is:
Exiting using System.exit()
In this example, we tried to read a file. If the file does not exist, we exit the program with System.exit() from the catch block. Please note that the finally block does not get executed if the file is not found. Because the System.exit() on the catch block exits the JVM and does not allow the finally block to be executed.
So as you see usage of System.exit() method suit better for script-based applications or wherever the status codes are interpreted. This is a convenient way to handle shutdown in bigger programs, where all parts of the program can’t (and shouldn’t) be aware of each other. Then, if someone wants to quit, he can simply call System.exit(), and the shutdown hooks (if properly set up) take care of doing all necessary shutdown ceremonies such as closing files, releasing resources etc.
3. Download the Source Code
You can download the full source code of this example here: Java System.exit() Example
