信用卡验证-技术上正确，但错误w/算法？

Question

import java.util.Scanner;

public class CreditCardTester{

public static void main(String[] args){

    Scanner scanner = new Scanner(System.in);
    String retry = ("y");
    String n = null;

    while(retry.equalsIgnoreCase("y")){ // allows program to keep running even if the user enters in a capital Y
        int lengthCheck = 1;
        System.out.println("Please enter your 8-digit credit card number");

    // check to see whether the input number is exactly 8 digits
        while(lengthCheck==1){
            n = scanner.next();
                if(n.length()==8)
                    lengthCheck=0;
                else
                    System.out.println("Please make sure the credit card number you have entered is 8 digits");
        } // end inner while loop

    // instantiate CardNumber and check validity
    CardNumber number = new CardNumber(n);
    number.check();
    if (number.isValid())
        System.out.println("The number you entered is a valid credit card number.");
    else
        System.out.println("The number you entered is not a valid credit card number. Would you like to enter in another number? (y/n)");
    retry = scanner.next();

    } // end outer while loop

}

}

public class CardNumber {

private String number;
private boolean valid;

public CardNumber(String n){
    number = n;
    valid = true;
}

private void check1(){
    int a = Integer.parseInt(number.substring(7));
    int b = Integer.parseInt(number.substring(5,6));
    int c = Integer.parseInt(number.substring(3,4));
    int d = Integer.parseInt(number.substring(1,2));

    int oddsum = a + b + c + d;

    int e = (Integer.parseInt(number.substring(6,7))) * 2;
    int f = (Integer.parseInt(number.substring(4,5))) * 2;
    int g = (Integer.parseInt(number.substring(2,3))) * 2;
    int h = (Integer.parseInt(number.substring(0,1))) * 2;

    String ee = String.valueOf(e);
    String ff = String.valueOf(f);
    String gg = String.valueOf(g);
    String hh = String.valueOf(h);

    int evensum = (Integer.parseInt(ee.substring(0))) + (Integer.parseInt(ff.substring(0))) + (Integer.parseInt(gg.substring(0))) + (Integer.parseInt(hh.substring(0)));

    int totalsum = evensum + oddsum;
    if (!(totalsum%10 == 0))
    valid=false;
}

public void check(){
    check1();
}

public boolean isValid(){
    return valid;
}

}

我相信还有一个更好的方法来做到这一点，所以所有的建议都很感激！

Answer 1

信用卡号验证称为Luhn算法。下面是一个java实现程序http://www.xinotes.org/notes/note/595/

对于您的代码，我认为这里是：

 int evensum = (Integer.parseInt(ee.substring(0))) + (Integer.parseInt(ff.substring(0))) + (Integer.parseInt(gg.substring(0))) + (Integer.parseInt(hh.substring(0)));

你的意思是把两个数字求和：

int evensum = Integer.parseInt(ee.substring(0,1)) +  Integer.parseInt(ee.substring(1)) ...