c++ - 类工厂创建派生类 C++

Question

我目前正在学习使用 C++ 的类工厂模式。我在尝试实现工厂时一直出错。假设我有一个抽象类和两个派生类。我想让工厂做的是像这样创建基类的新对象: Ball *sc = new SoccerBall();我不确定如何实现这一点，我已经尝试过但无济于事。我需要修复什么？

class Ball
{
   public:
   Ball();
   virtual ~Ball();
   virtual int getSize() const = 0;
   virtual void setBallSize(int s) = 0;
   virtual string ballManufacturer() const = 0;
   protected:
   int ballSize;
}
class Soccerball:public Ball
{
   public:
   Soccerball();
   Soccerball(int size);
   ~Soccerball();
   int getSize() const;
   void setBallSize(int s);
   string ballManufacturer() const;
}
class Soccerball:public Ball
{
   public:
   Soccerball();
   Soccerball(int size);
   ~Soccerball();
   int getSize() const;
   void setBallSize(int s);
   string ballManufacturer() const;
}
class Basketball:public Ball
{
   public:
   Basketball();
   Basketball(int size);
   ~Basketball();
   int getSize() const;
   void setBallSize(int s);
   string ballManufacturer() const;
}
class BallFactory
{
   public:
   Ball* createBall(string s)
   {
       if(s == "Soccer")
       {
          return new Soccerball(5);
       }
       if(s == "Basket")
       {
          return new Basketball(6);
       }
   }
}

Answer 1

这就是您的代码的工作方式，但在上面发布问题时，您应该提供“简短的自包含正确代码”，以便人们轻松理解您的问题。

#include <iostream>

using namespace std;

class Ball
{
  public:

    Ball()
    {
      cout<<"Ball ctr"<<endl;
    }

    virtual ~Ball()
    {

    }
    virtual int getSize() const = 0;
    virtual void setBallSize(int s) = 0;
    virtual string ballManufacturer() const = 0;

  protected:
    int ballSize;
};

class Soccerball:public Ball
{
  public:

    Soccerball()
    {
     cout<<"create Default Soccer Ball "<<endl;
    }

    Soccerball(int size)
    {
     cout<<"create Soccer Ball "<<size<<endl;
 }

    ~Soccerball()
    {

    }

    int getSize() const
    {
      return ballSize;
    }

    void setBallSize(int s)
    {
      ballSize = s;
    }

    string ballManufacturer() const
    {
      return "";
    }
};

class Basketball:public Ball
{
  public:

    Basketball()
    {
     cout<<"create default Baseket Ball "<<endl;
    }

    Basketball(int size)
    {
     cout<<"create Baseket Ball "<<size<<endl;
    }

 ~Basketball()
    {

    }

    int getSize() const
    {
      return ballSize;
    }

    void setBallSize(int s)
    {
      ballSize = s;
    }

    string ballManufacturer() const
    {
      return "";
    }
};

class BallFactory
{
  public:
//Factory method
    static Ball* createBall(string s)
    {
      if(s == "Soccer")
      {
        return new Soccerball(5);
      }
      if(s == "Basket")
      {
        return new Basketball(6);
      }
    }
};

int main()
{
  Ball* ptr = BallFactory::createBall("Soccer");

  return 0;
}

但您还需要了解工厂设计模式的工作原理、同名虚拟构造函数的创建方式以及使用参数化工厂的原因。或者你可以使用模板工厂。