设计模式——工厂方法模式（Factory Method）

• 创建一工厂接口，实例化延迟至子类（添加新对象，只需增加新的工厂子类）
• 解决简单工厂违反开闭原则的问题

• 

• 代码示例：

  #include <iostream>
  #include <string>
  using namespace std;
  
  //product
  class Shape 
  {
  public:
      virtual void draw() = 0;
      virtual ~Shape() {}
  };
  
  class Circle : public Shape 
  {
  public:
      void draw() { cout << "Circle::draw" << endl; }
      ~Circle() { cout << "Circle::~Circle" << endl; }
  private:
      Circle() {}
      friend class CircleFactory;
  };
  
  class Square : public Shape 
  {
  public:
      void draw() { cout << "Square::draw" << endl; }
      ~Square() { cout << "Square::~Square" << endl; }
  private:
      Square() {}
      friend class SqureFactory;
  };
  
  //factory
  class Factory
  {
  public:
      virtual Shape* create() = 0;
  };
  
  class CircleFactory : public Factory
  {
  public:
      Shape* create(){return new Circle;}
  };
  
  class SqureFactory : public Factory
  {
  public:
      Shape* create(){return new Square;}
  };
  
  int main() 
  {
      Factory *pFactory = new CircleFactory;//SqureFactory;
  
      Shape* pShape = pFactory->create();
  
      pShape->draw();
  
      delete pShape;
      delete pFactory;
  
      return 0;
  }