Polymorphism

Medium

In plain terms

Polymorphism allows different types to be used through a common interface. You call the same method name (e.g. speak()) on different objects (Dog, Cat), and each type runs its own implementation. The caller does not need to know the concrete type—they just use the interface.

This makes code flexible: you can add new types (e.g. Bird) without changing the code that calls speak(). Polymorphism is often achieved by inheritance (override methods) or by implementing the same interface. It is a key benefit of OOP for writing extensible, maintainable code.

What you need to know

•Same interface, different behavior
•Method overriding
•Extensibility without changing callers

Example

Code is language-agnostic in spirit; adapt the idea to your language:

function makeAnimalSpeak(animal) {
  console.log(animal.speak());  // Same call, different behavior
}
makeAnimalSpeak(new Dog("Rex"));   // Woof!
makeAnimalSpeak(new Cat("Whiskers")); // Meow!

Why this matters

Polymorphism is central to extensible design. Interviewers ask how you would add new types without changing existing code—polymorphism (and Open/Closed) is the answer.

How it connects

Achieved via inheritance (override methods) or interfaces (different implementations). It makes Open/Closed and Liskov Substitution practical: you can add new subtypes and plug them in where the base type is expected.

Interview focus

Be ready to explain these; they come up often.

▸Definition: same interface, different behavior; "many forms."
▸Two forms: overriding (inheritance) and implementing interface.
▸Benefit: callers depend on abstraction; new types can be added without changing callers.

Learn more

Dive deeper with these resources:

TutorialsPoint