c++类和对象---多态
1、多态的基本概念
多态是c++面向对象的三大特性之一
多态分为两类：
1、静态多态：函数重载和运算符重载属于静态多态，复用函数名
2、动态多态：派生类和虚函数实现运行时多态
静态多态和动态多态的区别
1、静态多态的函数地址早绑定 - 编译阶段确定函数地址
2、动态多态的函数地址晚绑定 - 运行阶段确定函数地址
动态多态满足条件：
1、有继承关系
2、子类重写父类虚函数（完全相同）
动态多态使用
父类指针或者引用，指向子类对象
class animal
{
public:
virtual void speak()
{
cout << "动物在说话" << endl;
}
int a_age;
};
class cat : public animal
{
void speak()
{
cout << "喵喵喵喵" << endl;
}
};
class dog : public animal
{
void speak()
{
cout << "汪汪汪汪" << endl;
}
};
//地址早绑定，在编译阶段确定函数地址
//如果想执行让猫说话，那么就不能让函数地址早绑定，做法，在父类的函数前加virtual，变成虚函数
void doSpeak(animal & animal)
{
animal.speak();
}
int main()
{
cat cat1;
doSpeak(cat1);
dog dog1;
doSpeak(dog1);
system("pause");
return 0;
}喵喵喵喵
汪汪汪汪
请按任意键继续. . .
案例：
分别利用普通写法和多态技术，实现两个操作数进行运算的计算器类
多态的优点：
1、代码组织结构清晰，可读性强
2、有利于前期和后期的扩展和维护
using namespace std;
//普通写法
class calculator
{
public:
int getResult(string oper)
{
if (oper == "+")
{
return m_num1 + m_num2;
}
else if (oper == "-") {
return m_num1 - m_num2;
}
else if (oper == "/") {
return m_num1 / m_num2;
}
else if (oper == "*") {
return m_num1 * m_num2;
}
}
int m_num1;
int m_num2;
};
void test01()
{
calculator c;
c.m_num1 = 10;
c.m_num2 = 2;
cout << c.m_num1 << "+" << c.m_num2 << "=" << c.getResult("+") << endl;
cout << c.m_num1 << "-" << c.m_num2 << "=" << c.getResult("-") << endl;
cout << c.m_num1 << "/" << c.m_num2 << "=" << c.getResult("/") << endl;
cout << c.m_num1 << "*" << c.m_num2 << "=" << c.getResult("*") << endl;
}
//多态实现计算器
class AbstractCalculator
{
public:
virtual int getResult()
{
return 0;
}
int m_num1;
int m_num2;
};
class addCalculator : public AbstractCalculator
{
public:
int getResult()
{
return m_num1 + m_num2;
}
};
class jianCalculator : public AbstractCalculator
{
public:
int getResult()
{
return m_num1 - m_num2;
}
};
class chengCalculator : public AbstractCalculator
{
public:
int getResult()
{
return m_num1 * m_num2;
}
};
void test02()
{
AbstractCalculator * abc = new addCalculator;
abc->m_num1 = 10;
abc->m_num2 = 2;
cout << abc->m_num1 << "+" << abc->m_num2 << "=" << abc->getResult() << endl;
delete abc;
abc = new jianCalculator;
abc->m_num1 = 10;
abc->m_num2 = 2;
cout << abc->m_num1 << "-" << abc->m_num2 << "=" << abc->getResult() << endl;
delete abc;
abc = new chengCalculator;
abc->m_num1 = 10;
abc->m_num2 = 2;
cout << abc->m_num1 << "*" << abc->m_num2 << "=" << abc->getResult() << endl;
delete abc;
}
int main()
{
//test01();
test02();
system("pause");
return 0;
}2、纯虚函数和抽象类
在多态中，通常父类中虚函数的实现是毫无意义的，主要都是调用子类重写的内容
因此可以将虚函数改为纯虚函数
纯虚函数语法：virtual 返回值类型 函数名 （参数列表） = 0；
当类中有了纯虚函数，这个类也称为抽象类
抽象类特点：
1、无法实例化对象
2、子类必须重写抽象类中的纯虚函数，否则也属于抽象类
//纯虚函数
class AbstractCalculator
{
public:
virtual int getResult() = 0;
int m_num1;
int m_num2;
};
class addCalculator : public AbstractCalculator
{
public:
};
class jianCalculator : public AbstractCalculator
{
public:
virtual int getResult()
{
return m_num1 - m_num2;
}
};
class chengCalculator : public AbstractCalculator
{
public:
int getResult()
{
return m_num1 * m_num2;
}
};
void test01()
{
/*
报错，纯虚函数属于抽象类，无法实例化对象
AbstractCalculator a;
new AbstractCalculator b;
*/
//addCalculator c;报错，子类没有重写父类中的纯虚函数，也不能实例化对象
jianCalculator abc;
abc.m_num1 = 10;
abc.m_num2 = 2;
cout << abc.m_num1 << "-" << abc.m_num2 << "=" << abc.getResult() << endl;
}
int main()
{
test01();
system("pause");
return 0;
}
案例2：制做饮品的大致流程：煮水-冲泡-倒入杯中-加入辅料
class abstractDrink
{
public:
virtual void boil() = 0;
virtual void brew() = 0;
virtual void pourInCup() = 0;
virtual void putSome() = 0;
void makeDrink()
{
boil();
brew();
pourInCup();
putSome();
}
};
class coffee : public abstractDrink
{
virtual void boil()
{
cout << "煮水" << endl;
}
virtual void brew()
{
cout << "冲咖啡" << endl;
}
virtual void pourInCup()
{
cout << "倒入杯中" << endl;
}
virtual void putSome()
{
cout << "加入咖啡伴侣" << endl;
}
};
class tea : public abstractDrink
{
virtual void boil()
{
cout << "煮水" << endl;
}
virtual void brew()
{
cout << "冲茶" << endl;
}
virtual void pourInCup()
{
cout << "倒入杯中" << endl;
}
virtual void putSome()
{
cout << "加入白糖" << endl;
}
};
void doWork(abstractDrink * abs)
{
abs->makeDrink();
delete abs;
}
void test01()
{
doWork(new coffee);
cout << "--------" << endl;
doWork(new tea);
}
int main()
{
test01();
system("pause");
return 0;
}3、虚析构和纯虚析构
多态使用时，如果子类中有属性开辟到堆区，那么父类指针在释放时无法调用到子类的析构代码
解决方式：将父类中的析构函数改为虚析构或纯虚析构
虚析构和纯虚析构共同点：
1、可以解决父类指针释放子类对象
2、都需要具体的函数实现
区别：
1、如果是纯虚析构，该类属于抽象类，无返实例化对象
虚析构语法：
virtual ~类名（）{}
纯虚析构语法：（需要声明也需要函数实现）！！！
类内声明：virtual ~类名（） = 0；
类外函数实现：类名：：~类名（）{}
class animal
{
public:
animal()
{
cout << "animal构造函数调用" << endl;
}
//虚析构
/*virtual ~animal()
{
cout << "animal析构函数调用" << endl;
}*/
//纯虚析构
virtual ~animal() = 0;
//纯虚函数
virtual void speak() = 0;
};
animal::~animal()
{
cout << "animal纯虚析构函数调用" << endl;
}
class cat : public animal
{
public:
cat(string name)
{
cout << "cat构造函数调用" << endl;
m_name = new string(name);
}
virtual void speak()
{
cout << *m_name << "喵喵喵" << endl;
}
~cat()
{
if (m_name != NULL)
{
cout << "cat析构函数调用" << endl;
delete m_name;
m_name = NULL;
}
}
string *m_name;
};
void test01()
{
animal * animal = new cat("tom");
animal->speak();//父类指针在析构时候，不会调用子类中析构函数，导致子类中如果有堆区属性，出现内存泄露
//解决方法，将父类析构函数变为虚析构，析构函数前面加“virtual”
delete animal;
}
int main()
{
test01();
system("pause");
return 0;
}animal构造函数调用
cat构造函数调用
tom喵喵喵
cat析构函数调用
animal纯虚析构函数调用
请按任意键继续. . .
总结：
- 虚析构或纯虚析构就是用来解决通过父类指针释放子类对象
- 如果子类中没有堆区数据，可以不写为虚析构或纯虚析构
- 拥有纯虚析构函数的类也属于抽象类
案例3
class CPU
{
public:
virtual void caculate() = 0;
};
class vidaoCard
{
public:
virtual void display() = 0;
};
class memory
{
public:
virtual void storage() = 0;
};
class computer
{
public:
computer(CPU * cpu, vidaoCard * vc, memory * mem)
{
m_cpu = cpu;
m_vc = vc;
m_mem = mem;
}
void work()
{
m_cpu->caculate();
m_vc->display();
m_mem->storage();
}
~computer() {
if (m_cpu != NULL)
{
delete m_cpu;
m_cpu = NULL;
}
if (m_vc != NULL)
{
delete m_vc;
m_vc = NULL;
}
if (m_mem != NULL)
{
delete m_mem;
m_mem = NULL;
}
}
private:
CPU * m_cpu;
vidaoCard * m_vc;
memory * m_mem;
};
class intercpu : public CPU
{
virtual void caculate()
{
cout << "inter的cpu开始工作" << endl;
}
};
class intervidao : public vidaoCard
{
virtual void display()
{
cout << "inter的vidaocard开始工作" << endl;
}
};
class intermemory : public memory
{
virtual void storage()
{
cout << "inter的memory开始工作" << endl;
}
};
class lenovocpu : public CPU
{
virtual void caculate()
{
cout << "lenovo的cpu开始工作" << endl;
}
};
class lenovovidao : public vidaoCard
{
virtual void display()
{
cout << "lenovo的vidaocard开始工作" << endl;
}
};
class lenovomemory : public memory
{
virtual void storage()
{
cout << "lenovo的memory开始工作" << endl;
}
};
void test01()
{
CPU * interCPU = new intercpu;
vidaoCard * intercard = new intervidao;
memory * intermem = new intermemory;
computer * computer1 = new computer(interCPU, intercard, intermem);
computer1->work();
delete computer1;
}
int main()
{
test01();
system("pause");
return 0;
}