NewBankAccountController creates a new BankAccountController with the specified BankAccount.

BankAccount represents a bank account with a balance.

BankAccountCommand is a class responsible for writing data to the BankAccount.

BankAccountController is a class responsible for handling user input and coordinating between the view, query, and command objects.

BankAccountQuery is a class responsible for reading data from the BankAccount.

BankAccountView is a class responsible for displaying the BankAccount balance to the user.

Experience 2: Chúng ta có thể không cần define interface cho BankAccount struct bởi vì mục đích interface lúc này là giúp ta có thể dễ quản lý và sử dụng ở các package khác.