將數字的每一位分離(Dome)

import java.util.Scanner;
public class reward {
public static void main(String[] args) {
    int cardnumber; 
    System.out.println("請輸入會員卡卡號末四位數字：");
    Scanner input = new Scanner(System.in);
    cardnumber= input.nextInt();
    int gewei = cardnumber% 10; 
    int shiwei = cardnumber/ 10 % 10; 
    int baiwei = cardnumber/ 100 % 10; 
    int qianwei = cardnumber/ 1000;
    int sum = gewei + shiwei + baiwei + qianwei;
    System.out.println("會員卡號末位四位數字" + cardnumber + "各位之和： " + sum);
    boolean isLuck=sum>20;
    System.out.println("該使用者是幸運客戶嗎？" +isLuck);
    }
}