怎么测试接收的数字不是数字然后输出一句话

Question

  public static void main(String[] args) {        Scanner sc = new Scanner(System.in);        //接收成绩        System.out.println("请输入成绩");        int t = sc.nextInt();        if (t >= 90 && (t <= 100)) {            System.out.println("A");        } else if (t >= 80 && (t < 90)) {            System.out.println("B");        } else if (t >= 70 && (t < 80)) {            System.out.println("C");        } else if (t >= 60 && (t < 70)) {            System.out.println("D");        } else if (t >= 0 && (t < 60)) {            System.out.println("E");        }    }}