继承和多类的基础（C++）

代码一：

#include <iostream>
using namespace std;

class Fish
{
public:
bool isFreshWaterFish;

void Swim()
{
if (isFreshWaterFish)
cout << "Swims in lake" << endl;
else
cout << "Swims in sea" << endl;
}
};

class Tuna: public Fish
{
public:
Tuna()
{
isFreshWaterFish = false;
}
};

class Carp: public Fish
{
public:
Carp()
{
isFreshWaterFish = true;
}
};

int main()
{
Carp myLunch;
Tuna myDinner;

cout << "Getting my food to swim" << endl;

cout << "Lunch: ";
myLunch.Swim();

cout << "Dinner: ";
myDinner.Swim();

return 0;
}

通过公有继承，Tuna和Carp类将暴露基类共有方法swim

代码二：

#include <iostream>
using namespace std;

class Fish
{
public:
void Swim()
{
cout << "Fish swims!" << endl;
}
};

class Tuna:public Fish
{
public:
// override Fish::Swim
void Swim()
{
cout << "Tuna swims!" << endl;
}
};

void MakeFishSwim(Fish& InputFish)
{
// calling Fish::Swim
InputFish.Swim();
}

int main()
{
Tuna myDinner;

// calling Tuna::Swim
myDinner.Swim();

// sending Tuna as Fish
MakeFishSwim(myDinner);

return 0;
}

其中void MakeFishSwim(Fish& InputFish)将传入都看作Fish基类

代码三：

class Fish
{
public:
virtual void swim()
{
cout <<"Fish swim!!!"<<endl;
}
};
class Tuna :public Fish
{
public:
void swim()
{
cout << "Tuna swim in the sea" << endl;

}
};

class Carp :public Fish
{
public:
void swim()
{
cout << "Carp can swim in the lake" << endl;
}
};

void MakeFishSwim(Fish&inputFish)
{
//
inputFish.swim();

}
int main()
{
Carp myLunch;
Tuna myDinner;

MakeFishSwim(myDinner);
MakeFishSwim(myLunch);

system("pause");
return 0;

}

其中virtual 虚函数的优先级在派生类之后，这是典型的降级