android银行卡号验证算法详解

public class CheckIdCard {  /**   * 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));    if (bit == 'N') {      return false;    }    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) {    if (nonCheckCodeCardId == null        || nonCheckCodeCardId.trim().length() == 0        || !nonCheckCodeCardId.matches("//d+")) {      // 如果传的不是数据返回N      return 'N';    }    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');  }}