Master Software Design Patterns and Architecture in C++/

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Factory Method Examples

Factory Method Examples

See the factory method implemented in some examples.

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In this lesson, we’ll look at some examples of a simple factory method. We’ll make an interface (abstract class in the case of C++) named Window, and we will have two classes: DefaultWindow and Fancywindow, which will implement the Window. For object creation, we will have getNewWindow() as a concrete creator. Let’s take a look at its code.

We’ll create a factory method with simple pointers in this example.

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#include <iostream>
// Product
class Window{ 
  public: 
    virtual Window* clone() = 0; 
    virtual ~Window() {};
};
// Concrete Products 
class DefaultWindow: public Window { 
  public:
    DefaultWindow() {
      std::cout << "DefaultWindow" << '\n';
    }
  private:
    DefaultWindow* clone() { 
      std::cout << "DefaultWindow clone" << '\n';
      return new DefaultWindow();
    } 
};
class FancyWindow: public Window { 
  public:
    FancyWindow() {
	  std::cout << "FancyWindow" << '\n';
	}
  private:
    FancyWindow* clone() { 
      std::cout << "FancyWindow clone" << '\n';
      return new FancyWindow();
    } 
};
// Concrete Creator or Client
Window* getNewWindow(Window& oldWindow) { 
  return oldWindow.clone();
}
  
int main(){
  DefaultWindow defaultWindow;
  FancyWindow fancyWindow;
  
  const Window* defaultWindow1 = getNewWindow(defaultWindow);
  const Window* fancyWindow1 = getNewWindow(fancyWindow);
  
  delete defaultWindow1;
  delete fancyWindow1;
  
}

Note: We can’t create the Window class object because it’s an abstract class.

Code explanation

  • Lines 4–8: We created a Window abstract class with one pure virtual method clone() and one virtual destructor.

  • Lines 11–21: We created a DefaultWindow class that implements the Window. We created a constructor containing no parameters, which ...