public static void main(String[] args) {
      Scanner scan = new Scanner(System.in);
      System.out.println("숫자를 입력해줘");
      int num = 0;
      boolean isOk = false;
      while(!isOk) {
      try{
         num = Integer.parseInt(scan.nextLine());
         isOk = true;
      }catch(NumberFormatException nfe) {
         System.out.println("입력하라는 숫자입력");
      }
}