面向对象编程（C++）精品教学：第12章1.pptVIP

* * * * * * * * * * * * * 例12.4 虚函数和抽象基类的应用。 改写例12.1以Point为基类的点—圆—圆柱体类的层次结构，在程序中使用虚函数和抽象基类 类的层次结构是 顶层：抽象基类Shape(形状) Point(点), Circle(圆), Cylinder(圆柱体)都是Shape类的直接派生类和间接派生类。 12.4.3 应用实例 第(1)部分 #include iostream using namespace std; //声明抽象基类Shape class Shape {public: virtual float area( ) const {return 0.0;}//虚函数 virtual float volume() const {return 0.0;} //虚函数 virtual void shapeName() const =0; //纯虚函数 }; 第(2)部分 //声明Point类 class Point:public Shape {public: Point(float=0,float=0); void setPoint(float,float); float getX( ) const {return x;} float getY( ) const {return y;} virtual void shapeName( ) const {cout″Point:″;} friend ostream operator(ostream ,const Point ); protected: float x,y;}; Point::Point(float a,float b) {x=a;y=b;} void Point::setPoint(float a,float b) {x=a;y=b;} ostream operator(ostream output,const Point p) {output″[″p.x″,″p.y″]″; return output;} 第(3)部分 //声明Circle类 class Circle:public Point {public: Circle(float x=0,float y=0,float r=0); void setRadius(float); float getRadius( ) const; virtual float area( ) const; virtual void shapeName( ) const {cout″Circle:″;} //对纯虚函数进行再定义 friend ostream operator(ostream ,const Circle ); protected: float radius; }; Circle::Circle(float a,float b,float r):Point(a,b),radius(r){ } void Circle::setRadius(float r):radius(r){ } float Circle::getRadius( ) const {return radius;} float Circle::area( ) const {return 3.14159*radius*radius;} ostream operator(ostream output,const Circle c) {output″[″c.x″,″c.y″], r=″c.radius; return output; } 第(4)部分 //声明Cylinder类 class Cylinder:public Circle {public: Cylinder (float x=0,float y=0,float r=0,float h=0); void setHeight(float); virtual float area( ) const; virtual float volume( ) const; virtual void shapeName( ) const {cout″Cylinder:″;} //对纯虚函数进行再定义 friend ostream operator(ostream,const Cylinder); protected: float height; }; //定义Cylinder类成员函数 Cylinder::Cylinder(float a,float b,float r,float h) :Circle(a,b,r),height(h){ } void