Java校验银行卡是否正确的核心代码

/**    * 校验银行卡卡号    *    * @param cardId    * @return    */   public static boolean checkBankCard(String cardId) {     char bit = getBankCardCheckCode(cardId         .substring(0, cardId.length() - 1));     return cardId.charAt(cardId.length() - 1) == bit;   }   /**    * 从不含校验位的银行卡卡号采用 Luhm 校验算法获得校验位    *    * @param nonCheckCodeCardId    * @return    */   public static char getBankCardCheckCode(String nonCheckCodeCardId) {     int cardLenth = nonCheckCodeCardId.trim().length();     if (nonCheckCodeCardId == null || cardLenth == 0         || !nonCheckCodeCardId.matches("//d+")) {       throw new IllegalArgumentException("不是银行卡的卡号!");     }     char[] chs = nonCheckCodeCardId.trim().toCharArray();     int luhmSum = 0;     for (int i = chs.length - 1, j = 0; i >= 0; i--, j++) {       int k = chs[i] - '0';       if (j % 2 == 0) {         k *= 2;         k = k / 10 + k % 10;       }       luhmSum += k;     }     return (luhmSum % 10 == 0) ? '0' : (char) ((10 - luhmSum % 10) + '0');   }