class Customer {
    private String _name;              // Name of customer
    private final String _customerID;  // Logon ID
    private String _password;          // Logon password
    private Address _shippingAddress;  // Address to ship items to
    private Address _billingAddress;   // Billing address (if provided)

    // The name of a customer can be retrieved and set:
    public String getName() {return _name;}
    public void setName(String name) {_name = name;}

    // A customer ID can only be retrieved; it cannot be
    // changed:
    public String getCustomerID() {return _customerID;}
    
    // A password can only be set and validated with validate(),
    // not retrieved:
    public void setPassword(String password) {
        _password = password;
    }

    public Address getShippingAddress() { return _shippingAddress;}

    // If no billing address is supplied, it's the same as the
    // shipping address:
    public Address getBillingAddress() {
        if (_billingAddress != null)
            return _billingAddress;
        else
            return _shippingAddress;
    }

    // Check id and password to see if logon should succeed:
    public boolean validate(String id, String password) {
        return true;
    }

    // Access the customer's shopping cart:
    public ShoppingCart getCart() {return null;}

    // Bill the customer for a completed order:
    public void bill(Order order) {}
};