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);

        }

    }

}

Explanation

  • Line 12: In the try{} block, we use the FileReader() method to read a data.csv file.
  • Line 18: If an exception comes in the catch(){} block ,it throws the File not found exception. Then it prints it on the console.
  • Line 20: If an exception comes, it means we did not find a specified file and JVM should terminate with an error value > 0.

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 {

            // 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);

        }

    }

}

Explanation

  • Line 12: In the try{} block, we use the FileReader() method to read a Olivetti.csv file.
  • Line 16: If an exception comes in the catch(){} block, we print a File not found exception.
  • Line 18: If an exception comes, it means that we did not find a specified file and JVM should terminate (halt the program execution) with an errored value < 0, that is, -1
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