Treat Inputmismatchexception calculator

Question

I am making a calculator in java oo, and I would like to treat this exception but I don’t know how.

This is the main class.

public class Principal {

    public static void main(String[] args) {


        Calculadora calc = null;

        int opc = -1, num1, num2;
        Scanner sc = new Scanner(System.in);

        do {

            System.out.println("Entre com o primeiro numero: ");
            num1 = sc.nextInt();

            System.out.println("Entre com o segundo numero: ");
            num2 = sc.nextInt();

            menu();
            opc = sc.nextInt();


switch (opc) {

        case 0:
            break;

        case 1:

             calc = new Calculadora(new Soma(), num1, num2);
             System.out.println("\nResultado: " + calc);

            break;

        case 2:

            calc = new Calculadora(new Subtracao(), num1, num2);
            System.out.println("Resultado: " + calc + "\n");

            break;

        default:
            System.out.println("Opcao Invalida.");

            break;
    }


        } while(opc != 0);
    }

    static void menu() {

        System.out.println("\tEscolha uma Opcao ");
        System.out.println("0: Sair");
        System.out.println("1: Somar");
        System.out.println("2: Subtracao");
        System.out.print("Opcao: ");

    }
}

Answer 1

Do you really need a calculator class? Okay. There are several ways to treat the exception, I will present one of them, where he understands that something typed wrong should disregard and enter again with the data, no matter where the error was, but gives sophistication. I did so:

public class Principal {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        do {
            try {
                System.out.println("Entre com o primeiro numero: ");
                int num1 = sc.nextInt();
                System.out.println("Entre com o segundo numero: ");
                int num2 = sc.nextInt();
                menu(); //completa desnecessidade fazer isso
                int opc = sc.nextInt();
            } catch (InputMismatchException) {
                System.out.println("Você digitou algo irregular, vamos começar de novo");
                continue;
            }
            switch (opc) {
                case 0:
                    break;
                case 1:
                     System.out.println("\nResultado: " + new Calculadora(new Soma(), num1, num2));
                    break;
                case 2:
                    System.out.println("Resultado: " + new Calculadora(new Subtracao(), num1, num2) + "\n");
                    break;
                default:
                    System.out.println("Opcao Invalida.");
                    break;
            }
        } while (opc != 0);
    }

    static void menu() {
        System.out.println("\tEscolha uma Opcao ");
        System.out.println("0: Sair");
        System.out.println("1: Somar");
        System.out.println("2: Subtracao");
        System.out.print("Opcao: ");
    }
}

I put in the Github for future reference.

I improved the code as a whole. I couldn’t test because I didn’t make a Minimum, Complete and Verifiable Example. I take this opportunity to say that I do not like how Java treats input wrong data. Particularly I prefer to do without the use of exception and treat the error individually by the normal flow. It gives more work, but it gets better. But this is not the way Java works, although it can be done normally.

To do it right, in practice you’d have to write your own parser to avoid the exception.