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?

score 14 · Accepted Answer · edited May 23 '17 at 11:54

14

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().

edited May 23 '17 at 11:54

Community

1
1

answered Jan 02 '14 at 17:06

TypeIA

16,916
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3

Technically, a method should throw an exception if final cleanup may be needed, but good answer. – Mad Physicist Jan 02 '14 at 17:07

score 1 · Answer 2 · answered Jan 02 '14 at 17:10

The return should have been a break, just leaving the while-loop, so that scanner.close() is done.

System.exit is bad style, but feasible for a command line program. Not catching the exception would be somewhat the same: termination with a message, but then with a stack trace too. In this letting the function throw an exception would be the preferable way.

score 0 · Answer 3 · answered Dec 11 '15 at 17:10

return statement is used inside a method to come out of it.System.exit(0) is used in any method to come out of program. System.exit(0) terminates the program narmally.Whereas System.exit(1) terminates the program because of some error encountered in the program.

score -3 · Answer 4 · answered Feb 08 '17 at 12:26

-3

System.exit() terminates the program at the line of invocation. System.exit(1) terminates the program if an error occurs.

answered Feb 08 '17 at 12:26

Hemin

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System.exit(1) and return

4 Answers4