Topic 9. Inheritance and polymorphism

Goal: become familiar with the inheritance and polymorphism mechanisms in C#; learn to build class hierarchies that call base constructors and use virtual methods and overriding, to override the methods of the object class, and to check object types; master using polymorphic arrays, sealed classes, and custom exceptions.

Lecture contents

1. Inheritance and constructors — Inheritance · What is inherited · Derived class constructors
2. Virtual methods and polymorphism — Virtual methods and overriding · Polymorphism · Hiding members with new · The object class
3. Casting, sealed, and composition — Type casting · Sealed classes and methods · Custom exception classes · Composition versus inheritance
4. Examples and common mistakes — Example programs · Common mistakes

Practice and review

• Practice — 3 worked examples with complete code and output
• Tasks — 30 variants, each with tasks at three difficulty levels
• Summary — conclusions, self-check questions, and useful links