Stopping a while loop

I'm developing a system with JFrame from a pharmacy. It's a matter of faculty. In the box operator enters the quantity X of product that the customer chooses from a list of n products and then with the unit value of each product that is worth Y. At the end the system must show the total value of the purchase by multiplying X * Y =?. This code is simple to make and use the terminal or do it without problems. An example of how I control the loop through the terminal.

while (n == 0){
        System.out.printf("\nEscolha:\n\t1 - Inserir novo produto\n\t0 - Valor Total");
            k = input.nextInt();
            if(k == 1){
                System.out.println("Quantidade de produtos: ");
                    //recebe
                System.out.println("Valor unitário");
                    //recebe
                    valorFinal = valorFinal + (quantidade * valorUnitario);
            }
            if(k == 0){
                //qualquer coisa
                n++;
                //interrompe o laço e imprime o valor
            }
    }

Using JFrame it does not work like this, since it does not have the user to choose option 1 or 0. In this case I thought about creating a button [Add Product] and every time it was clicked the seller would add the products and the unit value and when it clicked on the [End Value] button the loop would be interrupted and the result would be shown.

int n = 0;
    double valorFinal = 0;

    while(n == 0){
        resposta = JOptionPane.showConfirmDialog(null, "Cadastrar nova compra?");
        if(resposta == JOptionPane.YES_OPTION){
            double qtdIten = Double.valueOf(jTextField1.getText());
            double valor = Double.valueOf(jTextField2.getText());

             valorFinal = (valorFinal + (valor * qtdIten));

        }
        else{
            jTextArea1.setText("Valor da compra: "+valorFinal);
            n++;
        }
    }

In a very amateurish way I made this attempt with a JOptionPane but it did not work.