第43课 继承的概念和意义

面向对象的高端课程都是和继承相关的,例如设计模式。

思考:

类与类之间是否存在直接的关联关系?

生活中的例子:

组合关系的程序描述:

 1 #include <iostream>
 2 #include <string>
 3 
 4 using namespace std;
 5 
 6 class Memory
 7 {
 8 public:
 9     Memory()
10     {
11         cout << "Memory()" << endl;
12     }
13     ~Memory()
14     {
15         cout << "~Memory()" << endl;
16     }
17 };
18 
19 class Disk
20 {
21 public:
22     Disk()
23     {
24         cout << "Disk()" << endl;
25     }
26     ~Disk()
27     {
28         cout << "~Disk()" << endl;
29     }   
30 };
31 
32 class CPU
33 {
34 public:
35     CPU()
36     {
37         cout << "CPU()" << endl;
38     }
39     ~CPU()
40     {
41         cout << "~CPU()" << endl;
42     }    
43 };
44 
45 class MainBoard
46 {
47 public:
48     MainBoard()
49     {
50         cout << "MainBoard()" << endl;
51     }
52     ~MainBoard()
53     {
54         cout << "~MainBoard()" << endl;
55     }    
56 };
57 
58 class Computer
59 {
60     Memory mMem;
61     Disk mDisk;
62     CPU mCPU;
63     MainBoard mMainBoard;
64 public:
65     Computer()
66     {
67         cout << "Computer()" << endl;
68     }
69     void power()
70     {
71         cout << "power()" << endl;
72     }
73     void reset()
74     {
75         cout << "reset()" << endl;
76     }
77     ~Computer()
78     {
79         cout << "~Computer()" << endl;
80     }
81 };
82 
83 int main()
84 {   
85     Computer c;
86     
87     return 0;
88 }

运行结果如下:

组合关系的特点:

实际工程中先考虑组合关系。组合关系能满足需求就用组合关系。

继承关系:

 

 示例:

子类继承了父类的mv和其他成员函数,所以打印出100。

子类不但可以继承父类的代码,而且还可以添加新代码,继承还有另一个层面的意义,那就是代码复用,如下:

 C语言使用已经存在的代码只能复制粘贴,C++则可以通过继承。

完成的程序如下:

 1 #include <iostream>
 2 #include <string>
 3 
 4 using namespace std;
 5 
 6 class Parent
 7 {
 8     int mv;
 9 public:
10     Parent()
11     {
12         cout << "Parent()" << endl;
13         mv = 100;
14     }
15     void method()
16     {
17         cout << "mv = " << mv << endl;
18     }
19 };
20 
21 class Child : public Parent
22 {
23 public:
24     void hello()
25     {
26         cout << "I'm Child calss!" << endl;
27     }
28 };
29 
30 int main()
31 {   
32     Child c;
33     
34     c.hello();
35     c.method();
36     
37     return 0;
38 }

 重要规则:

示例程序:

Child对象可以直接当做Parent对象使用的。

继承的意义:

继承示例:

  1 #include <iostream>
  2 #include <string>
  3 
  4 using namespace std;
  5 
  6 class Memory
  7 {
  8 public:
  9     Memory()
 10     {
 11         cout << "Memory()" << endl;
 12     }
 13     ~Memory()
 14     {
 15         cout << "~Memory()" << endl;
 16     }
 17 };
 18 
 19 class Disk
 20 {
 21 public:
 22     Disk()
 23     {
 24         cout << "Disk()" << endl;
 25     }
 26     ~Disk()
 27     {
 28         cout << "~Disk()" << endl;
 29     }   
 30 };
 31 
 32 class CPU
 33 {
 34 public:
 35     CPU()
 36     {
 37         cout << "CPU()" << endl;
 38     }
 39     ~CPU()
 40     {
 41         cout << "~CPU()" << endl;
 42     }    
 43 };
 44 
 45 class MainBoard
 46 {
 47 public:
 48     MainBoard()
 49     {
 50         cout << "MainBoard()" << endl;
 51     }
 52     ~MainBoard()
 53     {
 54         cout << "~MainBoard()" << endl;
 55     }    
 56 };
 57 
 58 class Computer
 59 {
 60     Memory mMem;
 61     Disk mDisk;
 62     CPU mCPU;
 63     MainBoard mMainBoard;
 64 public:
 65     Computer()
 66     {
 67         cout << "Computer()" << endl;
 68     }
 69     void power()
 70     {
 71         cout << "power()" << endl;
 72     }
 73     void reset()
 74     {
 75         cout << "reset()" << endl;
 76     }
 77     ~Computer()
 78     {
 79         cout << "~Computer()" << endl;
 80     }
 81 };
 82 
 83 class HPBook : public Computer
 84 {
 85     string mOS;
 86 public:
 87     HPBook()
 88     {
 89         mOS = "Windows 8";
 90     }
 91     void install(string os)
 92     {
 93         mOS = os;
 94     }
 95     void OS()
 96     {
 97         cout << mOS << endl;
 98     }
 99 };
100 
101 class MacBook : public Computer
102 {
103 public:
104     void OS()
105     {
106         cout << "Mac OS" << endl;
107     }
108 };
109 
110 int main()
111 {   
112     HPBook hp;
113     
114     hp.power();
115     hp.install("Ubuntu 16.04 LTS");
116     hp.OS();
117     
118     cout << endl;
119     
120     MacBook mac;
121     
122     mac.OS();
123     
124     return 0;
125 }

运行结果如下:

 小结:

原文地址:https://www.cnblogs.com/wanmeishenghuo/p/9574350.html