我想运行一个程序，它可以根据输入的号码确定信用卡号码的有效性和类型。编译器显示我的编码有错误的通知，但我无法检测到它在哪里。该程序也无法运行。下面是编码，

    import java.util.*;

    public class CreditCard {

        public static void main(String args[]) {
                String CType;(String number) {
                    if (number.startsWith("4"))
                        return "Visa";
                    else if (number.startsWith("5"))
                        return "MasterCard";
                    else if (number.startsWith("6"))
                        return "Discover";
                    else if (number.startsWith("37"))
                        return "American Express";
                    else
                        return "Unknown type";
                };
            Scanner input = new Scanner(System.in);

            System.out.println("Enter a credit card number: ");
            long number = input.nextLong();

            long total = sumOfEvenPlaces(number) + (sumOfOddPlaces(number)*2);

            if (isValid(total)) {
                System.out.println("The "+CType+" card number is valid");
            } else {
                System.out.println("The "+CType+" card number is invalid.");
            }
        }



        public static boolean isValid(long total) {
            if (total % 10 != 0) {
            } else {
                        return true;
                }
            return false;
        }

        public static int sumOfEvenPlaces(long number) {
            int sum = 0;
            int remainder;
            while (number % 10 != 0 || number / 10 != 0) {
                remainder = (int) (number % 10);

                sum = sum + getDigit(remainder * 2);
                number /= 100;
            }
            return sum;
        }

        public static int getDigit(int number) {
            if (number > 9) {
                return (number % 10 + number / 10);
            } 
            return number;
        }

        public static int sumOfOddPlaces(long number) {
            int sum = 0;
            int remainder;
            number /= 10;
            while (number % 10 != 0 || number / 10 != 0) {
                remainder = (int) (number % 10);
                sum = sum + getDigit(remainder * 2);
                number /= 100;
            }
            return sum;
        }
    }

最佳答案

我用枚举检测卡片类型:

package com.gabrielbauman.gist;

import java.util.regex.Pattern;

public enum CardType {

    UNKNOWN,
    VISA("^4[0-9]{12}(?:[0-9]{3}){0,2}$"),
    MASTERCARD("^(?:5[1-5]|2(?!2([01]|20)|7(2[1-9]|3))[2-7])\\d{14}$"),
    AMERICAN_EXPRESS("^3[47][0-9]{13}$"),
    DINERS_CLUB("^3(?:0[0-5]\\d|095|6\\d{0,2}|[89]\\d{2})\\d{12,15}$"),
    DISCOVER("^6(?:011|[45][0-9]{2})[0-9]{12}$"),
    JCB("^(?:2131|1800|35\\d{3})\\d{11}$"),
    CHINA_UNION_PAY("^62[0-9]{14,17}$");

    private Pattern pattern;

    CardType() {
        this.pattern = null;
    }

    CardType(String pattern) {
        this.pattern = Pattern.compile(pattern);
    }

    public static CardType detect(String cardNumber) {

        for (CardType cardType : CardType.values()) {
            if (null == cardType.pattern) continue;
            if (cardType.pattern.matcher(cardNumber).matches()) return cardType;
        }

        return UNKNOWN;
    }

}

然后您可以执行 CardType.detect("cardnumbergoeshere") 并返回 CardType.VISA 等。

单元测试在 the gist 结束.

为了验证，我有:

public boolean isValid(String cardNumber) {
    int sum = 0;
    boolean alternate = false;
    for (int i = cardNumber.length() - 1; i >= 0; i--) {
        int n = Integer.parseInt(cardNumber.substring(i, i + 1));
        if (alternate) {
            n *= 2;
            if (n > 9) {
                n = (n % 10) + 1;
            }
        }
        sum += n;
        alternate = !alternate;
    }
    return (sum % 10 == 0);
}

应该这样做。

编辑:修复了 DINERS_CLUB 中的转义字符

关于java - 信用卡类型和验证，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/20377978/