Validando cartão de crédito em java

import java.io.BufferedReader;
import java.io.InputStreamReader;

public class CCUtils {
public static final int INVALID = -1;
public static final int VISA = 0;
public static final int MASTERCARD = 1;
public static final int AMERICAN_EXPRESS = 2;
public static final int EN_ROUTE = 3;
public static final int DINERS_CLUB = 4;

private static final String [] cardNames =
{ "Visa" ,
"Mastercard",
"American Express",
"En Route",
"Diner's CLub/Carte Blanche",
};

/**
* Valid a Credit Card number
*/
public static boolean validCC(String number)
throws Exception {
int CardID;
if ( (CardID = getCardID(number)) != -1)
return validCCNumber(number);
return false;
}

/**
* Get the Card type
* returns the credit card type
* INVALID = -1;
* VISA = 0;
* MASTERCARD = 1;
* AMERICAN_EXPRESS = 2;
* EN_ROUTE = 3;
* DINERS_CLUB = 4;
*/
public static int getCardID(String number) {
int valid = INVALID;

String digit1 = number.substring(0,1);
String digit2 = number.substring(0,2);
String digit3 = number.substring(0,3);
String digit4 = number.substring(0,4);

if (isNumber(number)) {
/* ----
** VISA prefix=4
** ---- length=13 or 16 (can be 15 too!?! maybe)
*/
if (digit1.equals("4")) {
if (number.length() == 13 || number.length() == 16)
valid = VISA;
}
/* ----------
** MASTERCARD prefix= 51 ... 55
** ---------- length= 16
*/
else if (digit2.compareTo("51")>=0 && digit2.compareTo("55")<=0) {
if (number.length() == 16)
valid = MASTERCARD;
}
/* ----
** AMEX prefix=34 or 37
** ---- length=15
*/
else if (digit2.equals("34") || digit2.equals("37")) {
if (number.length() == 15)
valid = AMERICAN_EXPRESS;
}
/* -----
** ENROU prefix=2014 or 2149
** ----- length=15
*/
else if (digit4.equals("2014") || digit4.equals("2149")) {
if (number.length() == 15)
valid = EN_ROUTE;
}
/* -----
** DCLUB prefix=300 ... 305 or 36 or 38
** ----- length=14
*/
else if (digit2.equals("36") || digit2.equals("38") ||
(digit3.compareTo("300")>=0 && digit3.compareTo("305")<=0)) {
if (number.length() == 14)
valid = DINERS_CLUB;
}
}
return valid;

/* ----
** DISCOVER card prefix = 60
** -------- lenght = 16
** left as an exercise ...
*/

}

public static boolean isNumber(String n) {
try {
double d = Double.valueOf(n).doubleValue();
return true;
}
catch (NumberFormatException e) {
e.printStackTrace();
return false;
}
}

public static String getCardName(int id) {
return (id > -1 && id < cardNames.length ? cardNames[id] : "");
}

public static boolean validCCNumber(String n) {
try {
/*
** known as the LUHN Formula (mod10)
*/
int j = n.length();

String [] s1 = new String[j];
for (int i=0; i < n.length(); i++) s1[i] = "" + n.charAt(i);

int checksum = 0;

for (int i=s1.length-1; i >= 0; i-= 2) {
int k = 0;

if (i > 0) {
k = Integer.valueOf(s1[i-1]).intValue() * 2;
if (k > 9) {
String s = "" + k;
k = Integer.valueOf(s.substring(0,1)).intValue() +
Integer.valueOf(s.substring(1)).intValue();
}
checksum += Integer.valueOf(s1[i]).intValue() + k;
}
else
checksum += Integer.valueOf(s1[0]).intValue();
}
return ((checksum % 10) == 0);
}
catch (Exception e) {
e.printStackTrace();
return false;
}
}

/*
** For testing purpose
**
** java CCUtils [credit card number] or java CCUtils
**
*/
public static void main(String args[]) throws Exception {
String aCard = "";

if (args.length > 0)
aCard = args[0];
else {
BufferedReader input =
new BufferedReader(new InputStreamReader(System.in));
System.out.print("Card number : ");
aCard = input.readLine();
}
if (getCardID(aCard) > -1) {
System.out.println("This card is supported.");
System.out.println("This a " + getCardName(getCardID(aCard)));
System.out.println
("The card number " + aCard + " is "
+ (validCC(aCard)?" good.":" bad."));
}
else
System.out.println("This card is invalid or unsupported!");
}
}