林业大学第12章多态类.pptVIP

第12章 多态类;第12章 多态类;一、虚函数;一、虚函数;一、虚函数;class China : public Country { public: virtual void Display() {cout 中国是我们伟大的祖国。 endl;} }; class America: public Country { public: virtual void Display() {cout 美国和我们隔洋相对。 endl;} };;void main() { Country *pc,c; America am; China ch; pc = c; pc-Display(); pc = am; pc-Display(); pc = ch; pc-Display(); };一、虚函数;一、虚函数; virtual ~A() { coutDelete object of Aendl; } }; class B:public A { public: virtual void display() { coutdisplay Bendl; }; virtual ~B() { coutDelete object of Bendl; } }; void main() { 　A *pb=new B; 　pb-display(); 　delete pb; } ;二、纯虚函数和抽象类;#include iostream.h class Shape { public: Shape(double dfx = 0.0, double dfy = 0.0); virtual void Draw() = 0; //纯虚函数 protected: double FirstX; //第一点x坐标 double FirstY; //第一点y坐标 }; Shape::Shape(double dfx, double dfy) { FirstX = dfx; FirstY = dfy; };class Line : public Shape { public: Line(double dfx = 0.0, double dfy = 0.0, double dsx = 0.0, double dsy = 0.0) ; void Draw(); protected: double SecondX; //第二点x坐标 double SecondY; //第二点y坐标 };;Line::Line(double dfx, double dfy, double dsx, double dsy) : Shape(dfx,dfy) { SecondX = dsx; SecondY = dsy; };void Line::Draw() { cout 绘制一条直线，第一点坐标为：( FirstX , FirstY ) ，第二点坐标为：( SecondX , SecondY ) endl; } class Circle : public Shape { public: Circle(double dfx = 0.0, double dfy = 0.0, double dr = 0.0) ; void Draw(); protected: double Radius; //圆的半径 };