Introduction - If you have any usage issues, please Google them yourself
The existing Banking System
has three classes: Bank, Customer and Account. Each customer has at most one account and now one
credit card. Credit cards are being delivered to the customers using postal services including four-digit
pin codes. Each credit card is associated to exactly one bank account. A credit card holds credit card
number and customer id. No one can read the credit card number but the ATM machine. ATM machine
provides only two types of services: withdraw money and checking the balance.