用户输入正确的格式后，如何使扫描仪可重复几次

Question

I am trying convert the value of money from dollars to how much of each type of coin, in cent. I want to make this code repeatable without needing to rerun the script. The problem i came across is listed below;

• What is the other way to make this repeatable/ way to improve my code
• After use type the second input instead the code outputting the first output
• The catch exception invalidation checker won't work after second try
• How do i make this code repeatable in the format below

public class MakeChange {

    public static void main(String[] args) throws Exception {
        Scanner input = new Scanner(System.in);
        System.out.print("Enter a dollar amount:");
        boolean isValidAmount = false;
        String amountInString = input.nextLine();
        double amount = 0;
        try {
            if (amountInString.isEmpty() || amountInString.equals(" ")) {
                System.out.println("INVALID");
            }
        } catch (InputMismatchException e) {
            e.printStackTrace();
        }

        if (amountInString.chars().allMatch(Character::isAlphabetic)) {
            System.out.println("INVALID");
        } else {
            amount = Double.parseDouble(amountInString);
            isValidAmount = true;
            convert(amount);
        }
        while (isValidAmount = true) {
            System.out.print("Enter a dollar amount:");
            amountInString = input.nextLine();
            convert(amount);
        }
    }

    private static void convert(double amount) {
        int toonies;
        int loonies;
        int quarters;
        int dimes;
        int nickels;
        int remainingCents;

        remainingCents = (int) (amount * 100 + .5);
        toonies = remainingCents / 200;
        remainingCents %= 200;
        loonies = remainingCents / 100;
        remainingCents %= 100;
        quarters = remainingCents / 25;
        remainingCents %= 25;
        dimes = remainingCents / 10;
        remainingCents %= 10;
        nickels = remainingCents / 5;
        remainingCents %= 5;

        System.out.println("toonies:" + toonies + ";" + " loonies:" + loonies + ";" + " quarters:" + quarters + ";"
                + " dimes:" + dimes + ";" + " nickels:" + nickels);

    }
}

(Example expected format)

Enter a dollar amount:12 toonies:6; loonies:0; quarters:0; dimes:0; nickels:0 Enter a dollar amount:42 toonies:10; loonies:0; quarters:2; dimes:0; nickels:0 (Current problem) Enter a dollar amount:12 toonies:6; loonies:0; quarters:0; dimes:0; nickels:0 Enter a dollar amount:42' toonies:6; loonies:0; quarters:0; dimes:0; nickels:0

Answer 1

You can change the boolean into a method isValidAmount:

private static boolean isValidAmount(String input) {

      if (input.isEmpty() || input.equals(" ")) {
        System.out.println("INVALID input:" + input);
        return false;
      }

    if (input.chars().allMatch(Character::isAlphabetic)) {
      System.out.println("INVALID input: " + input );
      return false;
    } else {
      return true;
    }
  }

You can then move the boolean isValid to your while loop:

public static void main(String[] args) throws Exception {
    Scanner input = new Scanner(System.in);
    System.out.print("Enter a dollar amount:");
    String amountInString;

    while ((amountInString = input.nextLine()) != null && isValidAmount(amountInString)) {
      // remove the  System.out.print("Enter a dollar amount:"); from the while loop
      double amount = Double.parseDouble(amountInString);
      convert(amount);
    }
  }

this way the isValidAmount boolean is refreshed each iteration.

For formatting purposes place the System.out.print("Enter a dollar amount:"); in the convert method instead of the while loop.

private static void convert(double amount) {
        int toonies;
        int loonies;
        int quarters;
        int dimes;
        int nickels;
        int remainingCents;

        remainingCents = (int) (amount * 100 + .5);
        toonies = remainingCents / 200;
        remainingCents %= 200;
        loonies = remainingCents / 100;
        remainingCents %= 100;
        quarters = remainingCents / 25;
        remainingCents %= 25;
        dimes = remainingCents / 10;
        remainingCents %= 10;
        nickels = remainingCents / 5;
        remainingCents %= 5;

        System.out.println("toonies:" + toonies + ";" + " loonies:" + loonies + ";" + " quarters:" + quarters + ";"
                + " dimes:" + dimes + ";" + " nickels:" + nickels + ";" + " remainingCents:" + remainingCents);
        System.out.print("Enter a dollar amount:");

    }

The output for a few lines will now be:

Enter a dollar amount:26.50 toonies:13; loonies:0; quarters:2; dimes:0; nickels:0; remainingCents:0 Enter a dollar amount:2315.90 toonies:1157; loonies:1; quarters:3; dimes:1; nickels:1; remainingCents:0 Enter a dollar amount:1222 toonies:611; loonies:0; quarters:0; dimes:0; nickels:0; remainingCents:0 Enter a dollar amount:0.05 toonies:0; loonies:0; quarters:0; dimes:0; nickels:1; remainingCents:0 Enter a dollar amount:0.01 toonies:0; loonies:0; quarters:0; dimes:0; nickels:0; remainingCents:1