<First Head设计模式>装饰器模式使用前的代码设计

今天读到了<First Head设计模式>装饰器这一章,对文中一开始的例子比较感兴趣.文中介绍了一个咖啡售卖系统如何设计的问题.一开始是通过设计一个基类来计算所用的调料的价格,而用子类来计算特定品种的整体价格.

这里面比较感兴趣的是文中有一个子类的实现: 在子类中直接通过父类名::方法来调用父类的方法,之前不怎么用继承,感到比较新奇,就自己码代码尝试了下.

程序的UML图大致如下,真正重要的函数是cost()函数,用来得出咖啡的最终价格.

 1 //Beverage.h
 2 #pragma once
 3 #include <iostream>
 4 using namespace std;
 5 
 6 class Beverage
 7 {
 8 public:
 9     Beverage(bool bMilk, bool bSugar, double dCostMilk, double dCostSugar);
10     virtual ~Beverage();    //基类析构用virtual,为了保证多态析构时能够找到子类的析构函数(不用virtual,基类指针是找不到子类的析构函数的位置的)
11 
12     virtual double cost();
13     bool HasMilk();
14     bool HasSugar();
15 protected:
16 private:
17     bool m_bMilk;
18     bool m_bSugar;
19     double m_dCostMilk;
20     double m_dCostSugar;
21 };

 1 //Beverage.cpp
 2 #include "Beverage.h"
 3 
 4 Beverage::~Beverage()
 5 {
 6     cout << "Beverage is Over~" << endl;
 7 }
 8 
 9 Beverage::Beverage(bool bMilk, bool bSugar, double dCostMilk, double dCostSugar):
10 m_bMilk(bMilk), m_bSugar(bSugar), m_dCostMilk(dCostMilk), m_dCostSugar(dCostSugar)
11 {
12     cout << "Beverage Begins~" << endl;
13 }
14 
15 bool Beverage::HasMilk()
16 {
17     return m_bMilk;
18 }
19 
20 bool Beverage::HasSugar()
21 {
22     return m_bSugar;
23 }
24 
25 //计算配料最终花了多少钱
26 double Beverage::cost()
27 {
28     double sum0 = 0;
29     if(HasMilk())
30     {
31         sum0 += m_dCostMilk;
32     }
33 
34     if (HasSugar())
35     {
36         sum0 += m_dCostSugar;
37     }
38     return sum0;
39 }

//DarkRoastCoffee.h
#pragma once
#include "Beverage.h"

class DarkRoastCoffee : public Beverage
{
public:
    DarkRoastCoffee(double myCost,bool bMilk, bool bSugar, double dCostMilk, double dCostSugar);

    ~DarkRoastCoffee();

    double cost();
    char * Description();
    double GetMyCost();

private:
    double m_dMyCost;
};

 1 //DarkRoastCoffee.cpp
 2 #include "DarkRoastCoffee.h"
 3 
 4 //在子类的构造函数中,调用父类的有参构造函数.  注意初始化成员列表需要放在函数定义中,因为最后的")"后面要跟着"{"
 5 DarkRoastCoffee::DarkRoastCoffee(double myCost,bool bMilk, bool bSugar, double dCostMilk, double dCostSugar):Beverage(bMilk, bSugar, dCostMilk, dCostSugar), m_dMyCost(myCost)
 6 {
 7     cout << "DarkRoastCoffee Begins~" << endl;
 8 }
 9 
10 double DarkRoastCoffee::GetMyCost()
11 {
12     return m_dMyCost;
13 }
14 
15 DarkRoastCoffee::~DarkRoastCoffee()
16 {
17     cout << "DarkRoastCoffee is Over~" << endl;
18 }
19 
20 double DarkRoastCoffee::cost()
21 {
22     return    Beverage::cost() + GetMyCost();    

//注意此时用了父类::方法,这里的Beverage::cost()不必是static,因为在该方法执行时父类对象已经创建了(若是在无继承关系的别的类中,cost必须要是static了)
//当然这里Beverage::cost()也不能是static,因为static函数不能为virtual.
24 }

输出结果:

 1 //CoffeeCost.cpp
 2 
 3 #include "Beverage.h"
 4 #include "DarkRoastCoffee.h"
 5 
 6 int main()
 7 {
 8     DarkRoastCoffee dc(10, false, true, 2, 4);
 9     cout << dc.cost() << endl;
10     return 0;
11 }

新战场:https://blog.csdn.net/Stephen___Qin