狂神说java计算器代码，有错误请指出谢谢

    public static void main(String[] args) {
        System.out.println("欢迎使用计算机");
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入第一个数");
        double i =scanner.nextDouble();
        System.out.println("请选择操作");
        System.out.println("1加，2减，3乘，4除");
        int j = scanner.nextInt();//对j赋值为加减乘除4个符号
        System.out.println("请输入第二个数");
        double z = scanner.nextDouble();
        while (j == 4 && z == 0){ // 除数不可为0
            System.out.println("除数不能为0，请重新输入第二个数");
            z = scanner.nextDouble();
        }
        double result = 0;
        switch (j){
            case 1:
                result=(double)i + z;
                break;
            case 2:
                result=i - z;
                break;
            case 3:
                result=i * z;
                break;
            case 4:
                result=i / z;
                break;
            default:
                break;
        }
        System.out.println("计算结果为"+result);
        scanner.close();
        }
    }