1. 多态的基本概念1
多态的基本概念
多态是c++面向对象三大特性之一
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
#include <iostream>
using namespace std;
class Animal
{
public:
/*void speak()
{
cout << "动物在说话" << endl;
}*/
//虚函数
virtual void speak()
{
cout << "动物在说话" << endl;
}
};
class Cat :public Animal
{
public:
//函数重写 函数返回值类型 函数名 参数列表 完全相同
void speak()
{
cout << "小猫在说话" << endl;
}
};
class Dog :public Animal
{
public:
void speak()
{
cout << "小狗在说话" << endl;
}
};
//执行说话的函数
//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,那么这个函数第地址就不能提前绑定,需要在运行阶段进行绑定,就是地址晚绑定
//1.动态多态满足条件
//2.子类要重写父类中的虚函数
//动态多态使用
//父类的指针或者引用 指向子类对象
void doSpeak(Animal &animal) //Animal & animal = cat;
{
animal.speak();
}
void test01()
{
Cat cat;
doSpeak(cat);
Dog dog;
doSpeak(dog);
}
void test02()
{
cout << "sizeof Animal=" << sizeof(Animal) << endl;
}
int main()
{
test01(); //第一次执行结果是动物在说话
test02(); //不加virtual是1 加了是4
system("pause");
return 0;
}
3. 多态案例一——计算机类
多态优点:
代码组织结构清晰--哪里出错了很容易看出
可读性强
利于前期和后期的扩展以及维护
#include <iostream>
using namespace std;
#include <string>
//多态案例
// 分别利用普通写法和多态技术,设计实现两个操作数进行运算的计算机类
//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;
}
//如果想扩展新的功能,需要修改源码
//在真是开发中 提倡 开闭原则
//开闭原则:对扩展进行开放,对修改进行关闭
}
int m_Num1;
int m_Num2;
};
void test01()
{
//创建一个计算器对象
Calculator c;
c.m_Num1 = 10;
c.m_Num2 = 10;
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;
}
//利用多态实现计算器
//实现计算器的基类
class AbstractCalculator
{
public:
virtual int getResult()
{
return 0;
}
int m_Num1;
int m_Num2;
};
//加法计算器类
class AddCalculator :public AbstractCalculator
{
public:
int getResult()
{
return m_Num1 + m_Num2;
}
};
//减法计算器类
class SubCalculator :public AbstractCalculator
{
public:
int getReseult()
{
return m_Num1 - m_Num2;
}
};
//乘法计算器类
class MulCalculator :public AbstractCalculator
{
public:
int getResult()
{
return m_Num1 * m_Num2;
}
};
void test02()
{
//多态使用条件
//父类指针或者引用指向子类对象
//加法运算
AbstractCalculator * abc = new AddCalculator;
abc->m_Num1 = 100;
abc->m_Num2 = 100;
cout << abc->m_Num1 << "+" << abc->m_Num2 << " = " << abc->getResult() << endl;
//用完后记得销毁
delete abc;
//减法运算
abc = new SubCalculator;
abc->m_Num1 = 100;
abc->m_Num2 = 100;
cout << abc->m_Num1 << "-" << abc->m_Num2 << " = " << abc->getResult() << endl;
//用完后记得销毁
delete abc;
//乘法运算
abc = new MulCalculator;
abc->m_Num1 = 100;
abc->m_Num2 = 100;
cout << abc->m_Num1 << "*" << abc->m_Num2 << " = " << abc->getResult() << endl;
//用完后记得销毁
delete abc;
}
int main()
{
//test01();
test02();
system("pause");
return 0;
}
4. 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:
无法实例化对象
子类必须重写抽象类中的纯虚函数,否则也属于抽象类
#include <iostream>
using namespace std;
//纯虚函数和抽象类
class Base
{
public:
/*virtual void func()
{
}
改为*/
virtual void func() = 0;//纯虚函数,只要有一个纯虚函数,这个类称为抽象类
//抽象类特点:
//无法实例化对象
// 子类必须重写抽象类中的纯虚函数,否则也属于抽象类
};
class Son :public Base
{
public:
//virtual void func() {}; //重写后 Son s; 不报错了
virtual void func()
{
cout << "func函数调用" << endl;
}
};
void test01()
{
//抽象类无法实例化对象
//Base b; //报错
//new Base; //报错
// 子类必须重写抽象类中的纯虚函数,否则也属于抽象类
//Son s; ///报错
Son s;
Base * base = new Son;
base->func();
}
int main()
{
test01();
system("pause");
return 0;
}
5. 多态案例二——饮品类
制作饮品大致流程为:煮水-冲泡-倒入杯中-加入辅助佐料
利用多态技术实现本案例,提供抽象制作饮品基类,提供子类制作咖啡和茶叶
#include <iostream>
using namespace std;
class AbstractDrinking
{
public:
//煮水
virtual void Boil() = 0;
//冲泡
virtual void Brew() = 0;
//倒入杯中
virtual void PourInCup() = 0;
//加入辅助佐料
virtual void PutSomething() = 0;
//制作饮品
void makeDrink()
{
Boil();
Brew();
PourInCup();
PutSomething();
}
};
//制作咖啡
class Coffee :public AbstractDrinking
{
public:
//煮水
virtual void Boil()
{
cout << "煮水" << endl;
}
//冲泡
virtual void Brew()
{
cout << "冲泡咖啡" << endl;
}
//倒入杯中
virtual void PourInCup()
{
cout << "倒入杯子" << endl;
}
//加入辅助佐料
virtual void PutSomething()
{
cout << "加入辅料" << endl;
}
};
//制作茶叶
class Tea :public AbstractDrinking
{
public:
//煮水
virtual void Boil()
{
cout << "煮水" << endl;
}
//冲泡
virtual void Brew()
{
cout << "冲泡茶叶" << endl;
}
//倒入杯中
virtual void PourInCup()
{
cout << "倒入杯子" << endl;
}
//加入辅助佐料
virtual void PutSomething()
{
cout << "加入辅料" << endl;
}
};
//制作函数
void doWork(AbstractDrinking * abs) //AbstractDrinking * abs = new Coffee
{
abs->makeDrink();
delete abs; //释放
}
void test01()
{
//制作咖啡
doWork(new Coffee);
cout << "----------------------" << endl;
//制作茶叶
doWork(new Tea);
}
int main()
{
test01();
system("pause");
return 0;
}
6. 虚析构和纯虚析构
多态使用后,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
的析构函数,
解决方法:将父类中的析构函数改为虚析构和纯虚析构
虚析构和纯虚析构共性:
可以解决父类指针释放子类对象
都需要有具体的函数实现
虚析构和重虚析构区别:
如果是纯虚析构,该类属于抽象类,无法实例化对象
虚析构语法:
virtual ~类名() {}
纯虚析构语法:
virtual ~类名() = 0;
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,可以不写虚析构和纯虚析构
拥有纯虚析构函数的类也属于抽象类
#include <iostream>
using namespace std;
#include <string>
class Animal
{
public:
Animal()
{
cout << "Animal构造函数调用" << endl;
}
//利用虚析构解决父类指针释放子类对象不干净的问题
//virtual ~Animal()
//{
// cout << "Animal析构函数调用" << endl;
//}
//纯虚析构 需要声明也需要实现
//有了纯虚析构之后 这个类也属于抽象类 无法实现实例化对象
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 << "小猫在说话" << endl;
}
string *m_Name;
~Cat()
{
if (m_Name != NULL)
{
cout << "Cat析构函数调用" << endl;
delete m_Name;
m_Name = NULL;
}
}
};
void test01()
{
Animal * animal = new Cat("Tom");
animal->speak();
//父类指针在析构时候 不会调用子类中的析构函数 导致子类中如果有堆区属性 出现内存泄漏
delete animal;
}
int main()
{
test01();
system("pause");
return 0;
}
7.多态案例三——电脑组装
#include <iostream>
using namespace std;
class CPU
{
public:
virtual void calculate() = 0;
};
class VideoCard
{
public:
virtual void display() = 0;
};
class Memory
{
public:
virtual void storage() = 0;
};
class Computer
{
public:
Computer(CPU * cpu, VideoCard * vc, Memory * mem)
{
m_cpu = cpu;
m_vc = vc;
m_mem = mem;
}
void work()
{
m_cpu->calculate();
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;
VideoCard * m_vc;
Memory * m_mem;
};
class IntelCPU :public CPU
{
public:
virtual void calculate()
{
cout << "Intel的CPU开始计算了" << endl;
}
};
class IntelVideoCard :public VideoCard
{
public:
virtual void display()
{
cout << "Intel的显卡开始显示了" << endl;
}
};
class IntelMemory :public Memory
{
public:
virtual void storage()
{
cout << "Intel的内存条开始存储了" << endl;
}
};
class LenovoCPU :public CPU
{
public:
virtual void calculate()
{
cout << "Lenovo的CPU开始计算了" << endl;
}
};
class LenovoVideoCard :public VideoCard
{
public:
virtual void display()
{
cout << "Lenovo的显卡开始显示了" << endl;
}
};
class LenovoMemory :public Memory
{
public:
virtual void storage()
{
cout << "Lenovo的内存条开始存储了" << endl;
}
};
void test01()
{
CPU * intelCpu = new IntelCPU;
VideoCard * intelCard = new IntelVideoCard;
Memory * intelMem = new IntelMemory;
Computer * computer1 = new Computer(intelCpu, intelCard, intelMem);
computer1->work();
delete computer1;
Computer * computer2 = new Computer(new LenovoCPU,new LenovoVideoCard,new LenovoMemory);
computer2->work();
delete computer2;
}
int main()
{
test01();
system("pause");
return 0;
}