Best practice for adding a bidirectional relation in OO model

Question

I\'m struggling to come up with a good way of adding a bidirectional relation in OO model. Let\'s say there is a Customer who can place many Orders, that is to say there is a on

Answer 1

If you are maintaining the bidirectional relationship in Customer.placeOrder(Order), why don't you do the same thing in Order.setCustomer(Customer)?

class Order {
    private Customer customer;
    public void setCustomer (Customer c) {
        customer = c;
        c.getOrders().add(this);
        // ... or Customer.placeOrder(this)
    }
}

It seems like duplicating code but it solves the problem. The simpler thing to do though is to avoid bidirectional relationships where possible.