C++_day8pm_多态

1.什么是多态

　　

　　

2.

　　

　　示例代码：　　

 #include <iostream>

 using namespace std;

 //形状:位置、绘制
 //+--圆形:半径、（绘制）
 //+--矩形:长宽、（绘制）
 //形状
 class Shape{
 public:
         Shape(int x, int y): m_x(x), m_y(y){}
         virtual void draw(void) const
         {
             cout << "形状(" << m_x << ',' << m_y << ')' << endl;
         }

 protected:
     int m_x;
     int m_y;
 };

 //圆形
 class Circle: public Shape{
 public:
     Circle(int x, int y, int r): Shape(x, y), m_r(r){}
     void draw(void) const
     {
         cout << "圆形（" << m_x << ',' << m_y << ',' << m_r << ')' << endl;
     }
 private:
     int m_r;
 };

 //矩形
 class Rectangle: public Shape{
 public:
     Rectangle(int x, int y, int w, int h): Shape(x, y), m_w(w), m_h(h){}
     void draw(void) const
     {
         cout << "矩形(" << m_x << ',' << m_y << ',' << m_w << ',' << m_h << ')' << endl;
     }
 private:
     int m_w;
     int m_h;
 };

 void render(Shape* shapes[])
 {
     for(size_t i = ; shapes[i]; ++i)
         shapes[i]->draw();
 }

 void drawAny(Shape const& shape)
 {
     shape.draw();
 }

 int main(void)
 {
     Shape* shapes[] = {};
     shapes[] = new Circle (,,);
     shapes[] = new Circle(,,);
     shapes[] = new Rectangle(,,,);
     shapes[] = new Rectangle(,,,);
     shapes[] = new Circle(,,);
     render(shapes);
     /*
     Circle c(18,19,20);
     Shape& r = c;
     r.draw();
     */
     Circle cr(,,);
     drawAny(cr);
     Rectangle rc(,,,);
     drawAny(rc);

     return ;
 }

协变类型只能是指针或者引用，不能是对象。

纯抽象类：

　　全部由纯虚函数构成的抽象类称为纯抽象类或者接口。

动态： 编译阶段产生，运行阶段执行。

 //模板方法模式---好莱坞模式
 #include <iostream>

 using namespace std;

 class Parser{
 public:
     void parse(char const* filename)
     {
         cout << "开始解析" << filename << "文件..." << endl;
         drawText();
         drawCircle();
         drawRectangle();
         drawImage();
         cout << "解析" << filename << "文件完成！" << endl;
     }

 private:
     virtual void drawText(void) = ;
     virtual void drawCircle(void) = ;
     virtual void drawRectangle(void) = ;
     virtual void drawImage(void) = ;

 };

 class Render: public Parser{
 private:
     void drawText(void)
     {
         cout << "绘制文字..." << endl;
     }
     void drawCircle(void)
     {
         cout << "绘制圆形..." << endl;
     }
     void drawRectangle(void)
     {
         cout << "绘制矩形..." << endl;
     }
     void drawImage(void)
     {
         cout << "绘制图像..." << endl;
     }
 };

 int main(void)
 {
     Render render;
     render.parse("stdc++.pdf");

     return ;
 }

 注：虚表放在类中，虚表指针放在对象中。