How do I repeat an entire program until manually terminated?

Question

My code works fine except for the part where I am supposed to ask the user if they would like to quit the program. It's a simple y/n that should trigger the entire program to repeat if 'n' is entered and terminates when 'y' is entered. I know i need to use a while loop but i just can't figure out exactly how I need to write it in code so that it works like expected.

import java.util.*;

public class MilitaryTime 

{

public static void main (String [] args)    
{

            Scanner in = new Scanner(System.in);
            int hour1, minute1, hour2, minute2;

            System.out.print("Please enter the first time: ");
            int time1 = in.nextInt();
            System.out.println();
            hour1 = time1 / 100;
            minute1 = time1 % 100;

            System.out.print("Please enter the second time: ");
            int time2 = in.nextInt();
            System.out.println();
            hour2 = time2 / 100;
            minute2 = time2 % 100;

            System.out.println("Time elapsed: " + (Math.abs(hour1 - hour2) + " Hours, " + (Math.abs(minute1 - minute2) + " Minutes \n")));

            System.out.print("Do you want to quit? (y/n): ");
            String answer = in.next();

            while (answer != "n")
            {

            }

    }

}

^^ i.e. change `while (answer != "n")` to `while(!answer.equals("n"))` — drew moore, Jun 22 '14 at 21:08

score 1 · Accepted Answer · answered Jun 22 '14 at 21:15

You should probably split your code in (at least) two different methods, but I'll just try to point out a way to achieve what you want with minimal changes:

public static void main (String [] args)    
{
    String answer = null;  // you have no answer yet...
    do {   // ... but you want to execute your stuff at least once
        Scanner in = new Scanner(System.in);
        int hour1, minute1, hour2, minute2;

        System.out.print("Please enter the first time: ");
        int time1 = in.nextInt();
        System.out.println();
        hour1 = time1 / 100;
        minute1 = time1 % 100;

        System.out.print("Please enter the second time: ");
        int time2 = in.nextInt();
        System.out.println();
        hour2 = time2 / 100;
        minute2 = time2 % 100;

        System.out.println("Time elapsed: " + (Math.abs(hour1 - hour2) + " Hours, " + (Math.abs(minute1 - minute2) + " Minutes \n")));

        System.out.print("Do you want to quit? (y/n): ");
        answer = in.next();
    } while (!answer.equalsIgnoreCase("n"));

}

score 0 · Answer 2 · answered Jun 22 '14 at 21:09

0

Until then rerun the main method.

while (answer.equals("n")) // comment by drewmoore; its helpfull for strings..
{
    // you said, program should repeat if n is pressed. 
    // so, if answer is equal to n then execute the main function.
    main();
}

This would execute until the user presses some other button.

Secondly, you don't need to use while loop. This can be done using if too.

answered Jun 22 '14 at 21:09

Afzaal Ahmad Zeeshan

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(1) Where exactly would the code that invokes `main()` be located ? I assume you wanted to advice that all that code should be extracted in a method other than `main`. (2) Since the `answer` is only available after the first iteration, this can only be achieved with a `do...while` loop. – Costi Ciudatu Jun 22 '14 at 21:21

How do I repeat an entire program until manually terminated?

2 Answers2