3.3 将实值对象改为引用对象

【1】源代码

 1 #include <QString>
 2 class Customer
 3 {
 4 public:
 5     Customer(QString name)
 6     {
 7         m_name = name;
 8     }
 9 
10     QString getName()
11     {
12         return m_name;
13     }
14 
15 private:
16     QString m_name;
17 };
18 
19 class Order
20 {
21 public:
22     Order(QString customerName)
23     {
24        m_pCustomer = new Customer(customerName);
25     }
26 
27     QString getCustomerName()
28     {
29        return m_pCustomer->getName();
30     }
31 
32     void setCustomer(QString customerName)
33     {
34        m_pCustomer = new Customer(customerName);
35     }
36 
37 private:
38     Customer *m_pCustomer;
39 };
40 
41 static int numberOfOrdersFor(QList<Order> orders, QString customer)
42 {
43     int result = 0;
44     QList<Order>::iterator iter = orders.begin();
45     while (iter != orders.end())
46     {
47        Order order = (Order)(*iter++);
48        if (order.getCustomerName().compare(customer) == 0)
49        {
50            ++result;
51        }
52     }
53 
54     return result;
55 }

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

  1 #include <QString>
  2 class Customer
  3 {
  4 public:
  5     Customer(QString name)
  6     {
  7         m_name = name;
  8     }
  9 
 10     QString getName()
 11     {
 12         return m_name;
 13     }
 14 
 15 private:
 16     QString m_name;
 17 };
 18 
 19 class Order
 20 {
 21 public:
 22     Order(int nID, Customer *pCustomer)
 23     {
 24        m_nID = nID;
 25        m_pCustomer = pCustomer;
 26     }
 27 
 28     int getID()
 29     {
 30         return m_nID;
 31     }
 32     Customer* getCustomer()
 33     {
 34         return m_pCustomer;
 35     }
 36 
 37 private:
 38     int m_nID;
 39     Customer *m_pCustomer; // 引用对象
 40 };
 41 
 42 class CustomerList
 43 {
 44 public:
 45     CustomerList()
 46     {
 47         loadCustomers();
 48     }
 49 
 50     Customer *getByName(QString name)
 51     {
 52         QList<Customer*>::iterator iter = m_pCustomerList.begin();
 53         while (iter != m_pCustomerList.end())
 54         {
 55             if ((*iter)->getName().compare(name) == 0)
 56             {
 57                 return (*iter);
 58             }
 59             ++iter;
 60         }
 61 
 62         m_pCustomerList.append(new Customer(name));
 63         return (m_pCustomerList.back());
 64     }
 65 
 66 private:
 67     void loadCustomers()
 68     {
 69        m_pCustomerList.append(new Customer("Wang"));
 70        m_pCustomerList.append(new Customer("Liu"));
 71        m_pCustomerList.append(new Customer("Sun"));
 72     }
 73 
 74 private:
 75     QList<Customer*> m_pCustomerList;
 76 };
 77 
 78 
 79 int main(int argc, char *argv[])
 80 {
 81     QCoreApplication a(argc, argv);
 82 
 83     CustomerList customList;
 84     QList<Order*> OrderList;
 85     OrderList.append(new Order(1, customList.getByName("Liu")));
 86     OrderList.append(new Order(2, customList.getByName("Wang")));
 87     OrderList.append(new Order(3, customList.getByName("Sun")));
 88     OrderList.append(new Order(4, customList.getByName("Liu")));
 89     OrderList.append(new Order(5, customList.getByName("Wang")));
 90     OrderList.append(new Order(6, customList.getByName("Sun")));
 91     OrderList.append(new Order(7, customList.getByName("Zheng")));
 92     for (int i = 0; i < OrderList.size(); ++i)
 93     {
 94         qDebug() << "order ID :: " << OrderList[i]->getID() << "Customer :: " << OrderList[i]->getCustomer();
 95     }
 96 
 97     return a.exec();
 98 }
 99 
100 // run out:
101 /*
102 order ID ::  1 Customer ::  0x206348
103 order ID ::  2 Customer ::  0x206250
104 order ID ::  3 Customer ::  0x206a28
105 order ID ::  4 Customer ::  0x206348
106 order ID ::  5 Customer ::  0x206250
107 order ID ::  6 Customer ::  0x206a28
108 order ID ::  7 Customer ::  0x206da8
109 */

【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.

顺序选择循环总结