“Calculadora Java JoptionPane” Respostas de código

Calculadora Java JoptionPane

import java.util.Scanner;
import javax.swing.JOptionPane;
 
public class Calculator
{
    public static void main(String [] args)
    {
        Scanner norbel = new Scanner(System.in);
 
        int answer;
 
        String FNumber = JOptionPane.showInputDialog("Enter first Integer: ");
        int fnum = Integer.parseInt(FNumber);
        fnum = norbel.nextInt();     
        String operator = JOptionPane.showInputDialog("Operation:\n 1.Addition\n 2.Subtraction\n 3.Multiplication\n 4.Division\n");
        Integer opt = Integer.parseInt(operator);
 
 
        if(opt == 1)
        {
            String opt1 = JOptionPane.showInputDialog("Enter second Integer: ");
            int snum = Integer.parseInt(opt1);
            snum = norbel.nextInt();
            answer = fnum + snum;
            String ans = "Answer" +answer+ "!";
            JOptionPane.showMessageDialog(null,answer);
 
        if(opt == 2)
        {
            String opt2 = JOptionPane.showInputDialog("Enter second Integer: ");
            int snum = Integer.parseInt(opt2);
            snum = norbel.nextInt();
            answer = fnum -  snum;
            String ans = "Answer" +answer+ "!";
            JOptionPane.showMessageDialog(null,ans);
        }
        if(opt == 3)
        {
            String opt3 = JOptionPane.showInputDialog("Enter second Integer: ");
            int snum = Integer.parseInt(opt3);
            snum = norbel.nextInt();
            answer = fnum * snum;
            String ans = "Answer" +answer+ "!";
            JOptionPane.showMessageDialog(null,ans);
        }
        if(opt == 4)
        {
            String opt4 = JOptionPane.showInputDialog("Enter second Integer: ");
            int snum = Integer.parseInt(opt4);
            snum = norbel.nextInt();
            answer = fnum / snum;
            String ans = "Answer" +answer+ "!";
            JOptionPane.showMessageDialog(null,ans);
        }
        else
        {
            String error = "Error";
            JOptionPane.showMessageDialog(null, error);
        }
 
    }
}