What is the System.exit() function in Java?

Overview

This static System.exit() function ceases JVMJava Virtual Machine’s execution.

The status argument value tells us about the termination behavior.

Note: The status argument value calls the class runtime method, Runtime.getRuntime().exit(n), to get the current status.

Here, n can have the values -1, 0, or 1.

Syntax

public static void exit(int status)

Parameters

status : This is a mode of termination.

status > 0: stipulates abnormal termination.
status < 0: stipulates abnormal termination.
status = 0: normal termination of program execution.

Return value

This function does not return any value. It returns a SecurityException when it does not allow an exit on a specified status code.

Code

The code snippets below illustrate how the System.exit() function works on different status values.

`status = 0`

Let’s consider exit(0), where JVM will terminate at 0. This means a normal termination of the program:

// Load libraries
import java.util.*;
import java.lang.*;
// Main Class
public class EdPresso {
	// main method
	public static void main(String[] args)
	{
		int num[] = {12, 9, 13, 24, 35, 36, 7, 18, 4, 3};
		// iterator for num array
		for (int i = 0; i < num.length; i++) {
			if (num[i] <= 10) {
				System.out.println("--- exit(0) method called ---");
				System.exit(0); // Terminate java virtual machines
			}
			else{
				if(num[i] % 2 ==0){
					System.out.println("num["+i+"] = " + num[i]);
				}
				else
				{
					System.out.println("num["+i+"] = " + num[i]);
					System.out.println("--- exit(-1) method called ---");
					System.exit(-1);	
				}
			}
		}
		System.out.println("Code successfully ending the main()");
	}
}

Explanation

Line 14: The program exits successfully. That’s why the status value 0 is used. It signals JVMJava Virtual Machine to mark the program execution complete.
Line 24: We can also use non-zero values for abnormal program termination. By using 1,-1 as our termination values, the programmer has the advantage of setting some errors.
Line 29: We try to print that the main function terminates successfully and does not execute because of exit().

`status = 1`

Now let’s consider exit(1), where JVM will terminate at 1. This means an abnormal termination of the program:

// Load libraries
import java.util.*;
import java.lang.*;
import java.io.*;

// Main Class
public class EdPresso {
    // main method
    public static void main(String[] args) throws Exception {

        try {
            BufferedReader br = new BufferedReader(new FileReader("data.csv"));
            int i;
            while ((i = br.read()) != -1) {
                System.out.print((char) i);
            }
        } catch (IOException e) {
            System.out.println("Exception: " + e);
            System.out.println("\nJVM Ceased at +1");
            System.exit(1);
        }
    }
}

// Load libraries
import java.util.*;
import java.lang.*;
import java.io.*;

// Main Class
public class EdPresso {
    // main method
    public static void main(String[] args) throws Exception {
        try {
            // trying to read a csv file
            BufferedReader buffer = new BufferedReader(new FileReader("Olivetti.csv"));
            System.out.println("File is ready");
        } 
        catch (IOException e) {
            System.out.println(e + "\nJVM Ceased at -1");
            // JVM abnormal termination
            System.exit(-1);
        }
    }
}