Java Luhn algorithm Card Number Generator

   import java.util.List;
   import java.util.Stack;
   import java.util.Vector;

   public class RandomCardNumberGenerator {


public static final String[] MASTERCARD_PREFIX_LIST = new String[] { "0626" };


public static final String[] VISA_PREFIX_LIST = new String[] { "4539",
        "4556", "4916", "4532", "4929", "40240071", "4485", "4716", "4" };

public static final String[] MASTERCARD_PREFIX_LIST2 = new String[] { "51",
        "52", "53", "54", "55" };

public static final String[] AMEX_PREFIX_LIST = new String[] { "34", "37" };

public static final String[] DISCOVER_PREFIX_LIST = new String[] { "6011" };

public static final String[] DINERS_PREFIX_LIST = new String[] { "300",
        "301", "302", "303", "36", "38" };

public static final String[] ENROUTE_PREFIX_LIST = new String[] { "2014",
        "2149" };

public static final String[] JCB_PREFIX_LIST = new String[] { "35" };

public static final String[] VOYAGER_PREFIX_LIST = new String[] { "8699" };


static String strrev(String str) {
    if (str == null)
        return "";
    String revstr = "";
    for (int i = str.length() - 1; i >= 0; i--) {
        revstr += str.charAt(i);
    }

    return revstr;
}

static String completed_number(String prefix, int length) 
{

    String ccnumber = prefix;

    while (ccnumber.length() < (length - 1)) {
        ccnumber += new Double(Math.floor(Math.random() * 10)).intValue();
    }

    String reversedCCnumberString = strrev(ccnumber);

    List<Integer> reversedCCnumberList = new Vector<Integer>();
    for (int i = 0; i < reversedCCnumberString.length(); i++) {
        reversedCCnumberList.add(new Integer(String
                .valueOf(reversedCCnumberString.charAt(i))));
    }

    int sum = 0;
    int pos = 0;

    Integer[] reversedCCnumber = reversedCCnumberList
            .toArray(new Integer[reversedCCnumberList.size()]);
    while (pos < length - 1) {

        int odd = reversedCCnumber[pos] * 2;
        if (odd > 9) {
            odd -= 9;
        }

        sum += odd;

        if (pos != (length - 2)) {
            sum += reversedCCnumber[pos + 1];
        }
        pos += 2;
    }

    int checkdigit = new Double(
            ((Math.floor(sum / 10) + 1) * 10 - sum) % 10).intValue();
    ccnumber += checkdigit;

    return ccnumber;

}

public static String[] credit_card_number(String[] prefixList, int length,int howMany) 
{

    Stack<String> result = new Stack<String>();
    for (int i = 0; i < howMany; i++) {
        int randomArrayIndex = (int) Math.floor(Math.random()
                * prefixList.length);
        String ccnumber = prefixList[randomArrayIndex];
        result.push(completed_number(ccnumber, length));
    }

    return result.toArray(new String[result.size()]);
}

public static String[] generateMasterCardNumbers(int howMany) {
    return credit_card_number(MASTERCARD_PREFIX_LIST, 16, howMany);
}

public static String generateMasterCardNumber() {
    return credit_card_number(MASTERCARD_PREFIX_LIST, 16, 1)[0];
}

public static boolean isValidCreditCardNumber(String creditCardNumber) {
    boolean isValid = false;

    try {
        String reversedNumber = new StringBuffer(creditCardNumber)
                .reverse().toString();
        int mod10Count = 0;
        for (int i = 0; i < reversedNumber.length(); i++) {
            int augend = Integer.parseInt(String.valueOf(reversedNumber
                    .charAt(i)));
            if (((i + 1) % 2) == 0) {
                String productString = String.valueOf(augend * 2);
                augend = 0;
                for (int j = 0; j < productString.length(); j++) {
                    augend += Integer.parseInt(String.valueOf(productString
                            .charAt(j)));
                }
            }

            mod10Count += augend;
        }

        if ((mod10Count % 10) == 0) {
            isValid = true;
        }
    } catch (NumberFormatException e) {
    }

    return isValid;
}

private static int sumToSingleDigit(int k)
{
    if (k < 10)
    return k;
    return sumToSingleDigit(k / 10) + (k % 10);
}

 }