开闭原则（Open

开闭原则（Open - Closed Principle）

C++ 描述
开闭原则坏的示例，，增加图形的时候GraphicEditor需要变化

class Shape {public:    int m_type;};class Rectangle :public Shape{    Rectangle()    {        Shape::m_type = 1;    }};class Circle :public Shape{    Circle()    {        Shape::m_type = 2;    }};class GraphicEditor {public:    void drawCircle(Shape* r) {  }    void drawRectangle(Shape* r) {  }     void drawShape(Shape* s)      {        if (s->m_type == 1)            drawRectangle(s);        else if (s->m_type == 2)            drawCircle(s);    }};

开闭原则好的示例，增加图形的时候GraphicEditor不用变化

class Shape{public:    virtual void draw()=0;};class Rectangle :public Shape{public:    void draw()    {        // draw the rectangle    }};class Circle :public Shape{public:    void draw()    {        // draw the circle    }};class GraphicEditor {public:    void drawShape(Shape* s)     {        s->draw();    }};