The concept of abstract class is introduced by the teacher. It should be discussed that abstract classes serve as blueprints for other classes and cannot be instantiated. However, they are essential in designing class hierarchies. Real-world examples related to abstract classes and subclasses can be discussed by the teacher and students (e.g., class Computer with basic properties can be defined as an abstract class, and can be specialized to Console, Desktop, Laptop, and Mobile Phone, each with a specific set of properties, etc.). Another example could be geometric figures. Rectangle or triangle can be inherited from abstract class figure. When calculation girt and area of general figure we do not have exact formula. But we have exact formula for rectangle and triangle. Square can be inherited from rectangle. Students should discuss more examples of geometric figures and bodies.