49-多态的概念和意义

1、函数重写（override）回顾

2、多态的概念和意义

3、

4、

#include <iostream>
#include <string>

using namespace std;

class Parent
{
public:
virtual void print()
{
cout << "I'm Parent." << endl;
}
};

class Child : public Parent
{
public:
void print()
{
cout << "I'm Child." << endl;
}
};

void how_to_print(Parent* p)
{
p->print();     // 展现多态的行为
}

int main()
{
Parent p;
Child c;

how_to_print(&p);    // Expected to print: I'm Parent.
how_to_print(&c);    // Expected to print: I'm Child.

return 0;
}
I'm Parent.
I'm Child.

5、多态意义

6、静态联编和动态联编

#include <iostream>
#include <string>

using namespace std;

class Parent
{
public:
virtual void func()
{
cout << "void func()" << endl;
}

virtual void func(int i)
{
cout << "void func(int i) : " << i << endl;
}

virtual void func(int i, int j)
{
cout << "void func(int i, int j) : " << "(" << i << ", " << j << ")" << endl;
}
};

class Child : public Parent
{
public:
void func(int i, int j)
{
cout << "void func(int i, int j) : " << i + j << endl;
}

void func(int i, int j, int k)
{
cout << "void func(int i, int j, int k) : " << i + j + k << endl;
}
};

void run(Parent* p)
{
p->func(1, 2);     // 展现多态的特性
// 动态联编
}

int main()
{
Parent p;

p.func();         // 静态联编
p.func(1);        // 静态联编
p.func(1, 2);     // 静态联编

cout << endl;

Child c;

c.func(1, 2);     // 静态联编

cout << endl;

run(&p);       //动态联编
run(&c);       //动态联编

return 0;
}
void func()
void func(int i) : 1
void func(int i, int j) : (1, 2)

void func(int i, int j) : 3

void func(int i, int j) : (1, 2)
void func(int i, int j) : 3

7、小结

#include <iostream>
#include <string>

using namespace std;

class Boss
{
public:
int fight()
{
int ret = 10;

cout << "Boss::fight() : " << ret << endl;

return ret;
}
};

class Master
{
public:
virtual int eightSwordKill()
{
int ret = 8;

cout << "Master::eightSwordKill() : " << ret << endl;

return ret;
}
};

class NewMaster : public Master
{
public:
int eightSwordKill()
{
int ret = Master::eightSwordKill() * 2;

cout << "NewMaster::eightSwordKill() : " << ret << endl;

return ret;
}
};

void field_pk(Master* master, Boss* boss)
{
int k = master->eightSwordKill();
int b = boss->fight();

if( k < b )
{
cout << "Master is killed..." << endl;
}
else
{
cout << "Boss is killed..." << endl;
}
}

int main()
{
Master master;
Boss boss;

cout << "Master vs Boss" << endl;

field_pk(&master, &boss);

cout << "NewMaster vs Boss" << endl;

NewMaster newMaster;

field_pk(&newMaster, &boss);

return 0;
}
Master vs Boss
Master::eightSwordKill() : 8
Boss::fight() : 10
Master is killed...
NewMaster vs Boss
Master::eightSwordKill() : 8
NewMaster::eightSwordKill() : 16
Boss::fight() : 10
Boss is killed...