Inheritance and Polymorphism

This topic covers code reuse and runtime flexibility. You build class hierarchies, override methods, understand dynamic dispatch via the virtual table, distinguish overriding from overloading, and apply the Liskov substitution principle to keep hierarchies sound.

Relation 1 —

Write this relation with symbols exactly as in Programming in ANSI C / OOP with C++ — E. Balagurusamy before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.

Relation 2 —

Write this relation with symbols exactly as in Programming in ANSI C / OOP with C++ — E. Balagurusamy before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.

Relation 3 —

Write this relation with symbols exactly as in Programming in ANSI C / OOP with C++ — E. Balagurusamy before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.

Inheritance expresses specialisation: a subclass inherits the base’s members and can add or override behaviour, modelling an IS-A relationship. Polymorphism is what makes this powerful — a variable of the base type can hold any subclass object, and a virtual method call is dispatched at runtime to the object’s actual type through a vtable, so client code written against the base works with every subclass. This only stays correct if subclasses honour the base’s contract (Liskov substitution); a subclass that weakens guarantees breaks callers. Because deep inheritance is rigid, composition — building behaviour by holding other objects — is often preferred for flexibility.

State assumptions explicitly before using any relation for inheritance and polymorphism — steady state, uniform properties, linear elastic material, ideal gas, incompressible flow, etc., as applicable.

Wrong assumptions invalidate the entire solution even when the formula is correct. In OOP viva and GATE descriptive questions, listing valid assumptions often earns separate marks.

1. Read the question and list given data with SI units (common in OOP papers).
2. Draw a neat labelled diagram where applicable — examiners in Indian universities award diagram marks even when arithmetic slips.
3. Identify which relation from this topic applies to inheritance and polymorphism.
4. Use equation 1: .
5. Use equation 2: .
6. Substitute values, compute, and verify units and sign (direction).
7. State conclusion in one line — e.g. safe/unsafe, stable/unstable, feasible/infeasible.

Inheritance and Polymorphism appears in Java/C++ application development. In Indian it software curricula this topic is tested because it connects theory to classes, inheritance, and polymorphism.

GATE and semester exams often combine inheritance and polymorphism with earlier units — revise prerequisites before attempting mixed problems.

Industry interview panels sometimes ask: "Where did you use inheritance and polymorphism?" — answer with a lab, mini-project, or plant visit example if possible.

Students confuse overriding (same signature, runtime dispatch) with overloading (same name, different parameters, compile-time), and violate Liskov substitution with subclasses that break the base contract. Expecting static/private methods to be polymorphic is another error.

Before attempting inheritance and polymorphism problems, confirm you can:

1. Single versus multiple inheritance differs between Java and C++
2. Prefer composition over inheritance for flexibility
3. Liskov substitution: a subclass must honour the base contract

Revise the solved examples in Programming in ANSI C / OOP with C++ — E. Balagurusamy and one previous-year GATE or university paper for this unit.