Question

Design and implement an ADT in JAVA that represents a credit card. it should include the customer name, the account number, credit limit, the reward points and the account balance. The initialization operation should set the data to client-supplied values. The credit limit will be initializes to $5000 and reward points to 0. Next, write a method to validate the card number using the Luhn Algorithm and implement it as a part of initialization process. If the number is invalid, throw a custom exception with the message "Invalid Account Number".

Answer 1

Here is the completed code for this problem including test code (Test.java). Comments are included, go through it, learn how things work and let me know if you have any doubts or if you need anything to change. If you are satisfied with the solution, please rate the answer. Thanks

//CreditCard.java

public class CreditCard {

    // attributes

    private String customerName;

    private String accountNumber;

    private double creditLimit;

    private int rewardPoints;

    private double accountBalance;

    // constructor to initialize all fields

    public CreditCard(String customerName, String accountNumber,

             double creditLimit, int rewardPoints, double accountBalance) {

         // using isValid method, validating account number, if it is not valid,

         // throwing a CreditCardException

         if (!isValid(accountNumber)) {

             throw new CreditCardException("Invalid Account Number");

         }

         // if credit limit, or account balance is negative, throwing exception

         if (creditLimit < 0) {

             throw new CreditCardException("Invalid Credit Limit");

         }

         if (accountBalance < 0) {

             throw new CreditCardException("Invalid Account Balance");

         }

         // if reward points is negative, making it 0 (not throwing exception as

         // this is not very important)

         if (rewardPoints < 0) {

             rewardPoints = 0;

         }

         // assigning validated values

         this.customerName = customerName;

         this.accountNumber = accountNumber;

         this.creditLimit = creditLimit;

         this.rewardPoints = rewardPoints;

         this.accountBalance = accountBalance;

    }

    // private helper method to check if cardNum is a valid credit card number

    // using Luhn's algorithm

    private boolean isValid(String cardNum) {

         int sum = 0; // checksum

         // flag variable which will be true for every second digit from the rear

         // and false for any other digits

         boolean second = false;

         // looping through each characters on the card in reverse order

         for (int i = cardNum.length() - 1; i >= 0; i--) {

             // if current character is not a digit, returning false

             if (!Character.isDigit(cardNum.charAt(i))) {

                 return false;

             }

             // converting char to digit

             int digit = Character.digit(cardNum.charAt(i), 10);

             // if this is not a second digit, simply adding to sum

             if (!second) {

                 // adding digit to sum

                 sum += digit;

             } else {// otherwise

                 // doubling digit

                 int doubled = digit * 2;

                 // extracting last and first digits

                 int lastDigit = doubled % 10;

                 int firstDigit = doubled / 10;

                 // adding to sum

                 sum += lastDigit + firstDigit;

             }

             // inversing the value of second

             second = !second;

         }

         // checking if checksum ends with 0

         if (sum % 10 == 0) {

             // valid

             return true;

         } else {

             // invalid

             return false;

         }

    }

    // getters and setters

    public double getCreditLimit() {

         return creditLimit;

    }

    public void setCreditLimit(double creditLimit) {

         if (creditLimit > 0)

             this.creditLimit = creditLimit;

    }

    public int getRewardPoints() {

         return rewardPoints;

    }

    public void setRewardPoints(int rewardPoints) {

         if (rewardPoints > 0)

             this.rewardPoints = rewardPoints;

    }

    public double getAccountBalance() {

         return accountBalance;

    }

    public void setAccountBalance(double accountBalance) {

         if (accountBalance > 0)

             this.accountBalance = accountBalance;

    }

    public String getCustomerName() {

         return customerName;

    }

    public String getAccountNumber() {

         return accountNumber;

    }

    // returns a String containing field values

    public String toString() {

         return "customerName=" + customerName + ", accountNumber="

                 + accountNumber + ", creditLimit=" + creditLimit

                 + ", rewardPoints=" + rewardPoints + ", accountBalance="

                 + accountBalance;

    }

}

// CreditCardException class to represent a custom exception

class CreditCardException extends RuntimeException {

    public CreditCardException(String msg) {

         super(msg);

    }

}

//Test.java (tester program)

public class Test {

    public static void main(String[] args) {

         // inside a try catch block, creating and displaying two Cards

         try {

             // 12345678903555 is a valid credit card number

             CreditCard card1 = new CreditCard("Oliver", "745111417143",

                      20000, 100, 15000);

             // displaying the card details

             System.out.println("Card1: " + card1);

             // 745111417144 is NOT a valid credit card number, hence will

             // throw exception

             CreditCard card2 = new CreditCard("John", "745111417144", 42000,

                      0, 10000);

             System.out.println("Card2: " + card2);

         } catch (CreditCardException ex) {

             System.out.println("Error: " + ex.getMessage());

         }

    }

}

/*OUTPUT*/

Card1: customerName=Oliver, accountNumber=745111417143, creditLimit=20000.0, rewardPoints=100, accountBalance=15000.0

Error: Invalid Account Number