类和对象—多态

多态的基本语法

• 静态多态：函数重载和运算法重载属于静态多态 复用函数名
• 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

• 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

早绑定代码如下：

#include <iostream> using namespace std;class Animal{public:void speak(){cout << "动物在说话"<< endl;} }; class Cat:public Animal{public:void speak(){cout << "猫在说话" <<endl; } };void doSpeak(Animal &animal){ //这个函数是早绑定，在编译阶段就已经绑定，所以无论传进来的参数是啥，最终的结果都是 动物在说话 animal.speak(); }void test01(){Cat c1;doSpeak(c1); } int main(){test01();return 0; } #include <iostream> using namespace std;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 SubCalculator:public AbstractCalculator{ public:int getResult(){return m_Num1-m_Num2;} };class MulCalculator:public AbstractCalculator{ public:int getResult(){return m_Num1*m_Num2;} };void test01(){AbstractCalculator *p = new AddCalculator;p->m_Num1 = 100;p->m_Num2 = 100;cout << p->getResult() << endl;delete p;//减法运算p = new SubCalculator;p->m_Num1 = 100;p->m_Num2 = 100;cout << p->getResult() << endl;delete p;//乘法运算p = new MulCalculator;p->m_Num1 = 100;p->m_Num2 = 100;cout << p->getResult() << endl;delete p; } int main(){test01();return 0; }

晚绑定代码：

class Animal{public:virtual void speak(){ //加上virtual 关键字 变为虚函数cout << "动物在说话"<< endl;} }; void doSpeak(Animal &animal){ //Animal &animal = c1animal.speak(); }

总结：
动态多态的满足条件

有继承关系

子类重写父类的虚函数 //重写和重载不同，重写要求函数名称、返回值、参数列表完全相同

动态多态的使用
父类的指针或者引用 指向子类的对象

动态多态的原理剖析

void test02(){cout << sizeof(Animal) << endl; }

结果为4，说明是一个指针

计算器案例：

#include <iostream> using namespace std;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 SubCalculator:public AbstractCalculator{ public:int getResult(){return m_Num1-m_Num2;} };class MulCalculator:public AbstractCalculator{ public:int getResult(){return m_Num1*m_Num2;} };void test01(){AbstractCalculator *p = new AddCalculator;p->m_Num1 = 100;p->m_Num2 = 100;cout << p->getResult() << endl;delete p;//减法运算p = new SubCalculator;p->m_Num1 = 100;p->m_Num2 = 100;cout << p->getResult() << endl;delete p;//乘法运算p = new MulCalculator;p->m_Num1 = 100;p->m_Num2 = 100;cout << p->getResult() << endl;delete p; } int main(){test01();return 0; } 《新程序员》：云原生和全面数字化实践50位技术专家共同创作，文字、视频、音频交互阅读

总结

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