3.3 将实值对象改为引用对象

【1】源代码

#include <QString>
class Customer
{
public:
    Customer(QString name)
    {
        m_name = name;
    }

    QString getName()
    {
        return m_name;
    }

private:
    QString m_name;
};

class Order
{
public:
    Order(QString customerName)
    {
       m_pCustomer = new Customer(customerName);
    }

    QString getCustomerName()
    {
       return m_pCustomer->getName();
    }

    void setCustomer(QString customerName)
    {
       m_pCustomer = new Customer(customerName);
    }

private:
    Customer *m_pCustomer;
};

static int numberOfOrdersFor(QList<Order> orders, QString customer)
{
    int result = 0;
    QList<Order>::iterator iter = orders.begin();
    while (iter != orders.end())
    {
       Order order = (Order)(*iter++);
       if (order.getCustomerName().compare(customer) == 0)
       {
           ++result;
       }
    }

    return result;
}

到目前为止，客户Customer对象还是值对象value object。

即就算多份订单属于同一客户，但每个订单order对象还是拥有各自的客户Customer对象。

我希望改变这一现状：使得一旦发现同一客户拥有多份不同的订单，那么所有这些订单Order对象只可以共享同一个客户Customer对象。

【2】将实值对象改为引用对象

#include <QString>
class Customer
{
public:
    Customer(QString name)
    {
        m_name = name;
    }

    QString getName()
    {
        return m_name;
    }

private:
    QString m_name;
};

class Order
{
public:
    Order(int nID, Customer *pCustomer)
    {
       m_nID = nID;
       m_pCustomer = pCustomer;
    }

    int getID()
    {
        return m_nID;
    }
    Customer* getCustomer()
    {
        return m_pCustomer;
    }

private:
    int m_nID;
    Customer *m_pCustomer; // 引用对象
};

class CustomerList
{
public:
    CustomerList()
    {
        loadCustomers();
    }

    Customer *getByName(QString name)
    {
        QList<Customer*>::iterator iter = m_pCustomerList.begin();
        while (iter != m_pCustomerList.end())
        {
            if ((*iter)->getName().compare(name) == 0)
            {
                return (*iter);
            }
            ++iter;
        }

        m_pCustomerList.append(new Customer(name));
        return (m_pCustomerList.back());
    }

private:
    void loadCustomers()
    {
       m_pCustomerList.append(new Customer("Wang"));
       m_pCustomerList.append(new Customer("Liu"));
       m_pCustomerList.append(new Customer("Sun"));
    }

private:
    QList<Customer*> m_pCustomerList;
};


int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    CustomerList customList;
    QList<Order*> OrderList;
    OrderList.append(new Order(1, customList.getByName("Liu")));
    OrderList.append(new Order(2, customList.getByName("Wang")));
    OrderList.append(new Order(3, customList.getByName("Sun")));
    OrderList.append(new Order(4, customList.getByName("Liu")));
    OrderList.append(new Order(5, customList.getByName("Wang")));
    OrderList.append(new Order(6, customList.getByName("Sun")));
    OrderList.append(new Order(7, customList.getByName("Zheng")));
    for (int i = 0; i < OrderList.size(); ++i)
    {
        qDebug() << "order ID :: " << OrderList[i]->getID() << "Customer :: " << OrderList[i]->getCustomer();
    }

    return a.exec();
}

// run out:
/*
order ID ::  1 Customer ::  0x206348
order ID ::  2 Customer ::  0x206250
order ID ::  3 Customer ::  0x206a28
order ID ::  4 Customer ::  0x206348
order ID ::  5 Customer ::  0x206250
order ID ::  6 Customer ::  0x206a28
order ID ::  7 Customer ::  0x206da8
*/

【3】总结

从一个类衍生出许多彼此相等的实例，希望将它们替换为同一个对象。将这个值对象变为引用对象。

Good Good Study, Day Day Up.

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