Add random card number generator

Author: sualeh

src/test/java/com/example/CardNumberGenerator.java

@@ -0,0 +1,57 @@
+/*
+ *
+ * Credit Card Number
+ * https://github.com/sualeh/credit_card_number
+ * Copyright (c) 2014-2024, Sualeh Fatehi.
+ *
+ */
+
+package com.example;
+
+import java.util.Random;
+
+public class CardNumberGenerator {
+
+  public static int calculateCheckDigit(final String cardNumber) {
+    int sum = 0;
+    boolean alternate = true;
+
+    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 (10 - sum % 10) % 10;
+  }
+
+  public static String generateRandomCardNumber(final String bin) {
+    final Random random = new Random();
+    final StringBuilder cardNumber = new StringBuilder(bin);
+
+    // Generate the remaining digits except the last one
+    while (cardNumber.length() < 15) {
+      cardNumber.append(random.nextInt(10));
+    }
+
+    // Calculate the check digit
+    final int checkDigit = calculateCheckDigit(cardNumber.toString());
+    cardNumber.append(checkDigit);
+
+    return cardNumber.toString();
+  }
+
+  public static void main(final String[] args) {
+    final String bin = args[0];
+    final String cardNumber = generateRandomCardNumber(bin);
+    System.out.println("Generated Card Number: " + cardNumber);
+  }
+}