类的综合案例——纯虚函数与抽象类( 加强对接口与多态，以及派生类构造函数的理解 )

注意派生类构造函数的写法。
  1 #include <iostream>
  2 
  3 using namespace std;
  4 
  5 enum COLOR { Red, Green, Blue, Yellow, White, Black, Brown };
  6 
  7 class Animal
  8 {
  9 public:
 10     Animal() = default;
 11     Animal(int);
 12     virtual ~Animal();
 13     virtual int GetAge() const { return itsAge; }
 14     virtual void SetAge(int age) { itsAge = age; }
 15     virtual void Sleep() const = 0;                //抽象基类，有5个纯虚函数
 16     virtual void Eat() const = 0;
 17     virtual void Reproduce() const = 0;  //繁殖
 18     virtual void Move() const = 0;
 19     virtual void Speak() const = 0;
 20 private:
 21     int itsAge;
 22 };
 23 
 24 Animal::Animal(int age): itsAge(age)
 25 {
 26     cout << "Animal构造函数被调用...
";
 27 }
 28 Animal::~Animal()
 29 {
 30     cout << "Animal析构函数被调用...
";
 31 }
 32 
 33 class Mammal : public Animal
 34 {
 35 public:
 36     Mammal() = default;
 37     Mammal(int age) : Animal(age)   //将age传递给基类Animal的构造函数,使用基类的构造函数构造派生类的基类部分的成员
 38     {
 39         cout << "Mammal构造函数被调用...
";
 40     }
 41     virtual ~Mammal()
 42     {
 43         cout << "Mammal析构函数被调用...
";
 44     }
 45     virtual void Reproduce() const      //只覆盖了基类Animal的Reproduce函数,基类的其他4个纯虚函数没有重写，所以Mammal类还是一个抽象类(一个具有4个纯虚函数的抽象类)
 46     {
 47         cout << "Mammal reproduction depicted...
";
 48     }
 49 };
 50 
 51 class Fish : public Animal
 52 {
 53 public:
 54     Fish() = default;
 55     Fish(int age) : Animal(age)     //将age传递给基类Animal的构造函数,使用基类的构造函数构造派生类的基类部分的成员
 56     {
 57         cout << "Fish构造函数被调用...
";
 58     }
 59     virtual ~Fish()
 60     {
 61         cout << "Fish的析构函数被调用...
";
 62     }
 63     virtual void Sleep() const { cout << "Fish sleeping...
"; }     //Fish类实现了Animal类的所有纯虚函数，所以Fish类不是抽象类
 64     virtual void Eat() const { cout << "fish eating...
"; }
 65     virtual void Reproduce() const { cout << "fish reproducing...
"; }
 66     virtual void Move() const { cout << "Fish moving...
"; }
 67     virtual void Speak() const { cout << "Fish speaking...
"; };
 68 };
 69 
 70 class Horse : public Mammal
 71 {
 72 public:
 73     Horse() = default;
 74     Horse(int age, COLOR color) : Mammal(age), itsColor(color)
 75     {
 76         cout << "Horse构造函数被调用...
";
 77     }
 78     virtual ~Horse()
 79     {
 80         cout << "Horse析构函数被调用...
";
 81     }
 82     virtual void Speak() const { cout << "Horse speaking
"; }//由于Horse继承于Mammal,Mammal已经实现了Animal的Reproduce纯虚函数，所以horse只需实现剩余4个纯虚函数即可
 83     virtual void Sleep() const { cout << "Horse sleeping...
"; }
 84     virtual void Eat() const { cout << "Horse eating"; }
 85     virtual void Move() const { cout << "Horse Moving...
"; }
 86     virtual COLOR GetItsColor() const { return itsColor; }    //在继承关系中，最好将所有成员函数都声明为虚函数
 87 protected:
 88     COLOR itsColor;   //COLOR为前面定义的枚举类型
 89 };
 90 
 91 class Dog : public Mammal
 92 {
 93 public:
 94     Dog() = default;
 95     Dog(int age, COLOR color) : Mammal(age), itsColor(color)
 96     {
 97         cout << "Dog构造函数被调用...
";
 98     }
 99     virtual ~Dog()
100     {
101         cout << "Dog析构函数被调用...
";
102     }
103     virtual void Sleep() const { cout << "Dog sleeping...
"; }     
104     virtual void Eat() const { cout << "Dog eating...
"; }
105     virtual void Reproduce() const { cout << "Dog reproducing...
"; }  //覆盖了父类Mammal的reproduce函数
106     virtual void Move() const { cout << "Dog moving...
"; }
107     virtual void Speak() const { cout << "Dog speaking...
"; }
108 protected:
109     COLOR itsColor;
110 };
111 
112 int main()
113 {
114     Animal *pAnimal = nullptr;
115     int choice;
116     bool fQuit = false;
117     while (fQuit == false)
118     {
119         cout << "(1)Dog (2)Horse (3)Fish (0)Quit: ";
120         cin >> choice;
121         
122         switch (choice)         //pAnimal可以指向其任意的子类对象
123         {                       //此处体现了类的多态性
124         case 1:                
125             pAnimal = new Dog(5, Brown);
126             break;
127         case 2:
128             pAnimal = new Horse(4, Black);
129             break;
130         case 3:
131             pAnimal = new Fish(5);
132             break;
133         default:
134             fQuit = true;
135             break;
136         }
137         if (fQuit == false)
138         {
139             pAnimal->Speak();
140             pAnimal->Eat();
141             pAnimal->Reproduce();
142             pAnimal->Move();
143             pAnimal->Sleep();
144             delete pAnimal;
145             cout << endl;
146         }
147     }
148 
149     return 0;
150 }