System.exit(1) and return

Question

import java.io.FileNotFoundException;
import java.util.Formatter;
import java.util.FormatterClosedException;
import java.util.NoSuchElementException;
import java.util.Scanner;

public class CreateTextFile
{
    private Formatter formatter;

    public void openFile()
    {
        try
        {
            formatter = new Formatter("clients.txt");
        }

        catch (SecurityException securityException)
        {
            System.err.println("You do not have permission to access this file");
            System.exit(1);
        }

        catch (FileNotFoundException fileNotFoundException)
        {
            System.err.println("Error opening or creating the file");
            System.exit(1);
        }
    }

    public void addRecords()
    {
        AccountRecord accountRecord = new AccountRecord();
        Scanner scanner = new Scanner(System.in);

        System.out.printf("%s%n%s%n%s%n%s%n", "To terminate input, type the end-of-file indicator", "when you are prompted to enter input", "On Unix/Linux/Mac OS X type <control> d then press Enter", "On Windows type <ctrl> z then press Enter");

        while (scanner.hasNext())
        {
            try
            {
                accountRecord.setAccountNumber(scanner.nextInt());
                accountRecord.setFirstName(scanner.next());
                accountRecord.setLastName(scanner.next());
                accountRecord.setBalance(scanner.nextDouble());

                if (accountRecord.getAccountNumber() > 0)
                    formatter.format("%d %s %s %,.2f%n", accountRecord.getAccountNumber(), accountRecord.getFirstName(), accountRecord.getLastName(), accountRecord.getBalance());
                else
                    System.out.println("Account number must be greater than 0");
            }

            catch (FormatterClosedException formatterClosedException)
            {
                System.err.println("Error writing to file");
                return;
            }

            catch (NoSuchElementException noSuchElementException)
            {
                System.err.println("Invalid input. Try again");
                scanner.nextLine();
            }

            System.out.printf("%s %s%n%s", "Enter account number (>0),", "first name, last name and balance.", "?");
        }
        scanner.close();
    }

    public void closeFile()
    {
        if (formatter != null)
            formatter.close();
    }
}

I was just wondering why in openFile() the catch blocks are terminated with System.exit() and the catch blocks in addRecords() terminate with return. Is there a recommended way of when each should be used?

Answer 1

They do different things. return simply returns from the function to its caller and the program continues running. System.exit() terminates the program; control does not return to the caller.

You should use System.exit() when your program encounters an unrecoverable error and there is no point in the program continuing to run. Use return when your program can gracefully recover, or when the program should perform cleanup/closeout actions before exiting.

See also this more extended discussion of System.exit().