In object oriented programming, what is polymorphism and how does it relate to using a common interface for different underlying types?

Introduction / Context:
Polymorphism is one of the core ideas in object oriented programming and often appears in interview and exam questions. The word comes from Greek roots meaning many forms. In practical programming, polymorphism allows code to call methods on objects without knowing their exact concrete types at compile time. This question asks you to define polymorphism and explain how it relates to using a common interface for different types.

Given Data / Assumptions:

• We are working with classes and interfaces in an object oriented language.
• Different classes may implement the same interface or inherit from the same base class.
• Client code may hold references to the base type or interface rather than to concrete subclasses.
• The language runtime can dispatch method calls based on the actual object type at runtime.

Concept / Approach:
Polymorphism allows a single interface or base class type to represent many different concrete implementations. Code that deals with the interface type can invoke methods without needing to know which specific subclass instance is present. When a method is overridden in subclasses, the runtime chooses the appropriate implementation based on the dynamic type of the object. This mechanism, often called dynamic dispatch, enables flexible design patterns and decouples high level logic from low level details.

Step-by-Step Solution:
Step 1: Picture a base type, such as a Shape interface with a draw method, and subclasses like Circle and Rectangle that implement draw differently.Step 2: Client code holds a reference of type Shape and calls draw on it without caring whether the underlying object is a Circle or a Rectangle.Step 3: At runtime, the system inspects the actual object type and routes the call to Circle.draw or Rectangle.draw accordingly.Step 4: This ability of one interface method call to take many forms depending on the actual object type is polymorphism.Step 5: Recognise that polymorphism promotes loose coupling, extensibility, and cleaner designs because new subclasses can be added without changing existing client code.

Verification / Alternative check:
You can confirm polymorphic behaviour by creating a collection of base type references and filling it with different subclass instances. Iterating over the collection and calling a common method will invoke different implementations for each element. Object oriented textbooks use such examples to illustrate that polymorphism enables flexible and extensible systems by allowing new forms to be introduced through additional classes.

Why Other Options Are Wrong:
Option B talks about compiler optimisation, which is unrelated to object oriented polymorphism. Option C describes arrays, which are containers but do not by themselves convey polymorphic behaviour. Option D refers to compilation steps and has nothing to do with objects or interfaces. None of these alternatives capture the idea of different classes sharing a common interface and responding in different ways to the same method calls.

Common Pitfalls:
A common pitfall is to rely too heavily on type checks and downcasts instead of letting polymorphism work through virtual method calls. This often leads to bloated if else structures that are harder to maintain. Another mistake is misunderstanding the difference between compile time overloading and runtime overriding, both of which are sometimes called forms of polymorphism. Focusing on the central idea of using a common interface type and allowing method calls to be dispatched based on runtime type will help you design better object oriented systems.

Final Answer:
Correct answer: The ability of different classes to be treated through a common interface, where the same operation call can result in different behaviour depending on the actual object type