Case Study: Inheritance and Polymorphism in a Graphics Library

 

Inheritance and polymorphism are important concepts in object-oriented programming, and they can be used to create a powerful and flexible graphics library. Consider a scenario where we want to create a library for drawing shapes on a screen. We can define a base class called "Shape" that contains common properties and methods for all shapes, such as the color, position, and a method for drawing the shape.

Here's an example implementation of the "Shape" class in C++:

class Shape {
  protected:
    int x, y;
    std::string color;
  public:
Shape(int x, int y, std::string color) : 
x(x), y(y), color(color) {}
    virtual void draw() = 0;
};

The Shape class has three member variables: "x" and "y" for the position, and "color" for the color. It also has a constructor that initializes these variables, and a virtual method called "draw()" that must be implemented by any class that inherits from "Shape". The "virtual" keyword is used to indicate that the method can be overridden in derived classes.

Next, we can create derived classes for specific shapes, such as "Rectangle" and "Circle", that inherit from the "Shape" class and override the "draw()" method to provide their own implementation for drawing the shape.

Here's an example implementation of the "Rectangle" class:

class Rectangle : public Shape {
  private:
    int width, height;
  public:
    Rectangle(int x, int y, std:
:string color, int width, int height) :
 Shape(x, y, color), width(width), height(height) {}
    void draw() override {
        std::cout << "Drawing a rectangle at
 (" << x << "," << y << ") with color " 
<< color << " and size " << width << "x" 
<< height << std::endl;
    }
};

And here's an example implementation of the "Circle" class:

class Circle : public Shape {
  private:
    int radius;
  public:
    Circle(int x, int y, std::string color, int radius) : 
Shape(x, y, color), radius(radius) {}
    void draw() override {
        std::cout << "Drawing a circle at (" << x << "," << y << ")
 with color " << color << " and radius " << radius << std::endl;
    }
};

With these classes in place, we can create a graphics library that can draw different shapes, without having to worry about the specific details of each shape. We can use polymorphism to call the "draw()" method on objects of different shapes, without knowing their specific type.

Here's an example of how we can use the graphics library:

int main() {
    Shape *shapes[2];
shapes[0] = new Rectangle(10, 20, "red", 100, 50);
shapes[1] = new Circle(30, 40, "blue", 30);

    for (int i = 0; i < 2; i++) {
        shapes[i]->draw();
    }

    return 0;
}

In this example, we create an array of pointers to "Shape" objects, and initialize them with objects of

the "Rectangle" and "Circle" classes. We then use a for loop to iterate through the array and call the "draw()" method on each object, which will automatically call the correct implementation for each shape. This is the power of polymorphism: we can treat objects of different shapes as if they were all the same type, without having to worry about the specific details of each shape.

In conclusion, inheritance and polymorphism are key concepts in object-oriented programming that can be used to create a powerful and flexible graphics library. By creating a base class for common properties and methods, and then deriving specific classes for each shape, we can make use of polymorphism to easily draw different shapes on the screen, without having to worry about the specific details of each shape.