多态分为两类

• 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
• 动态多态: 派生类和虚图数实现运行时多态

静态多态和动态多态区别:

• 静态多态的函数地址早绑定 · 编译阶段确定函数地址
• 动态多态的函数地址晚绑定 · 运行阶段确定函数地址

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1、基本语法

#include <iostream>
using namespace std;
#include <string>//动物类
class Animal {
public://虚函数virtual void speak() {cout << "动物在说话" << endl;}
};//猫类 
class Cat :public Animal {
public://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;}
};//狗类
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，那么这个函数地址就不能提前绑定，需要在运行阶段进行绑定，地址晚绑定//动态多态满足条件
//1、有继承关系
//2、子类重写父类的虚函数//动态多态的使用
//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);
}int main() {test01();system("pause");return 0;
}

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2、案例1：计算器类

案例描述:
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器类

#include <iostream>
using namespace std;
#include <string>//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//在真正的开发中 提倡 开闭原则//开闭原则：对扩展进行开发，对修改进行关闭}int m_Num1;//操作数1int m_Num2;//操作数2
};void test01() {//创建计算器对象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
//多态好处：
// 1、组织结构清晰
// 2、可读性强
// 3、对前期和后期拓展和维护性高
//实现计算器抽象类
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 getResult() {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//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;abc = NULL;		//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;delete abc;abc = NULL;//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;delete abc;abc = NULL;}int main() {//test01();test02();system("pause");return 0;
}

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3、纯虚函数和抽象类

#include <iostream>
using namespace std;
#include <string>class Base {
public://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：//1、无法实例化对象//2、抽象类的子类 必须要重写父类中的纯虚函数，否则也属于抽象类virtual void func() = 0;
};class Son :public Base {
public:virtual void func() {cout << "fun()函数调用" << endl;}
};void test01() {//Base b;//抽象类无法实例化对象//new Base;//抽象类无法实例化对象//Son s;//子类必须重写父类中的纯虚函数，否则无法实例化对象Base* base = new Son;base->func();}int main() {system("pause");return 0;
}

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4、案例2：制作饮品

案例描述:
制作饮品的大致流程为: 煮水 冲泡 倒入杯中 加入辅料
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;
#include <string>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 << "煮农夫山泉" << endl;};//冲泡virtual void Brew() {cout << "冲泡咖啡" << endl;};//倒入杯中virtual void PourInCup() {cout << "倒入杯中" << endl;};//加入辅料virtual void PutSomething() {cout << "加入糖和牛奶" << endl;};
};//制作茶叶
class Tea :public AbstractDrinking {
public://煮水virtual void Boil() {cout << "煮矿泉水" << endl;};//冲泡virtual void Brew() {cout << "冲泡茶叶" << endl;};//倒入杯中virtual void PourInCup() {cout << "倒入杯中" << endl;};//加入辅料virtual void PutSomething() {cout << "加入枸杞" << 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;
}

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5、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

虚析构和纯虚析构区别:

• 如果是纯虚析构，该类属于抽象类，无法实例化对象

#include <iostream>
using namespace std;
#include <string>class Animal {
public:Animal() {cout << "Animal构造函数调用" << endl;}//利用虚析构可以解决 父类指针释放子类对象时不干净的问题/*virtual ~Animal(){cout<< "Animal虚析构函数调用" << endl;}*///纯虚析构 需要声明也需要实现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;}~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，导致子类如果有堆区属性，出现内存泄露delete animal;  
}int main() {test01();system("pause");return 0;
}

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6、案例三：电脑组装

• 电脑主要组成部件为 CPU (用于计算)，显卡 (用于显示)，内存条 (用于存储)
• 将每个零件封装出抽象基类，并且提供不同的厂商生产不同的零件，例如Intel厂商和Lenovo厂商
• 创建电脑类提供让电脑工作的函数，并且调用每个零件工作的接口
• 测试时组装三台不同的电脑进行工作

#include <iostream>
using namespace std;
#include <string>//抽象不同零件类//抽象CPU类
class CPU {
public://抽象的计算函数virtual void calculate() = 0;};//抽象显卡类
class VideoCard {
public://抽象的显示函数virtual void display() = 0;};//抽象内存条类
class Memory {
public://抽象的存储函数virtual void storage() = 0;};//电脑类
class Computer {
public:Computer(CPU* cpu, VideoCard* vc, Memory* mem) {m_cpu = cpu;m_vc = vc;m_mem = mem;}//提供工作的函数void work() {//让零件工作起来，调用接口m_cpu->calculate();m_vc->display();m_mem->storage();}//提供析构函数 释放3个电脑零件~Computer() {//释放cpu零件if (m_cpu != NULL) {delete m_cpu;m_cpu = NULL;}//释放显卡零件if (m_vc != NULL) {delete m_vc;m_vc = NULL;}//释放内存条零件if (m_mem != NULL) {delete m_mem;m_mem = NULL;}}private:CPU* m_cpu;//CPU的零件指针VideoCard* m_vc;//显卡零件指针Memory* m_mem;//内存条零件指针
};//具体厂商
//Intel厂商
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;}
};//Lenvo厂商
class LenvoCPU :public CPU {
public:virtual void calculate() {cout << "Lenvo的CPU开始计算了" << endl;}
};class LenvoVideoCard :public VideoCard {
public:virtual void display() {cout << "Lenvo的显卡开始显示了" << endl;}
};class LenvoMemory :public Memory {
public:virtual void storage() {cout << "Lenvo的内存条开始存储了" << endl;}
};void test01() {//第一台电脑零件CPU* intelCpu = new IntelCPU;VideoCard* intelCard = new IntelVideoCard;Memory* intelMem = new IntelMemory;cout << "第一台电脑开始工作" << endl;//创建第一台电脑Computer* computer1 = new Computer(intelCpu, intelCard, intelMem);computer1->work();delete computer1;cout << "---------------------" << endl;cout << "第二台电脑开始工作" << endl;//创建第二台电脑Computer* computer2 = new Computer(new LenvoCPU,new LenvoVideoCard,new LenvoMemory);computer2->work();delete computer2;cout << "---------------------" << endl;cout << "第三台电脑开始工作" << endl;//创建第三台电脑Computer* computer3 = new Computer(new LenvoCPU, new IntelVideoCard, new LenvoMemory);computer3->work();delete computer3;
}int main() {test01();system("pause");return 0;
}