What is the main difference between Inheritance and Polymorphism?

java

inheritance

polymorphism

oop

byAlex Kataev·Oct 9, 2024

Inheritance is a subclass drawing attributes and methods from a superclass, crucial for code reuse and constructing class hierarchies. Polymorphism enables different classes to respond differently to the same method call, typifying multiple forms (many shapes).

Animal, a superclass, has a makeSound() method inherited by Dog and Cat, each making their unique sound.

class Animal { void makeSound() { System.out.println("Generic sound"); } }
class Dog extends Animal { void makeSound() { System.out.println("Bark"); } } // "Who let dogs out?"
class Cat extends Animal { void makeSound() { System.out.println("Meow"); } } // "It's not over till the cat meows"

Executing makeSound() on different objects demonstrates Polymorphism:

new Dog().makeSound(); // "Bark"
new Cat().makeSound(); // "Meow"

Each subclass exemplifies Inheritance by extending Animal.

Access modifiers: Friends or Foes?

Understanding Inheritance calls for understanding access modifiers. While public and protected members of a superclass are inherited, private members aren't visible to subclasses, therefore, not inherited.

In direct contrast, Polymorphism comes alive with method overriding where protected and public methods get overridden, facilitating unique behaviors in subclasses.

Inheritance sans Polymorphism

You might think inheritance and polymorphism are always a package deal, but guess again! When a subclass inherits from its superclass without overriding inherited methods, we witness Inheritance without Polymorphism. The subclass is merely a carbon copy of the superclass – no uniqueness here folks!

Meanwhile, Polymorphism sans Inheritance flourishes through the implementation of interfaces or duck typing. Here, an object's method and property sets defy its eligibility for specific use.

Runtime Drama: Polymorphism in Display

With method overriding, Polymorphism steals the show as each subclass unleashes a personalized implementation of a superclass method. Remember the Animal example? When you called the makeSound() method on Dog or Cat, dynamic dispatch determined the appropriate implementation at runtime.

Beware: Overloading isn't Polymorphism just because it sorta sounds similar. It doesn't alter behavior at runtime but simply provides additional functionality within a class.

It’s not a Language Barrier, it’s a Feature!

The design and implementation of inheritance and polymorphism can drastically vary across programming languages. For instance, in the land of JavaScript, the prototype-based inheritance contrasts starkly with the class-based approach of Java. Here, objects inherit directly from other objects unlocking the mysteries of polymorphism through dynamic lookup.

C++, on the other hand, requires virtual methods to ensure that the correct subclass method will be called even when referenced through a superclass pointer.

Keep it DRY: Reusability and Maintainability

The underlying objectives of both inheritance and polymorphism are code reusability and maintainability. By extending classes or implementing interfaces, developers can write less and maintain easier. These concepts provide a flexible framework for Object-Oriented Programming (OOP) and drastically cut down on development time and testing efforts.

Predict the Unpredictable: Potential Pitfalls and Solutions

Strong as they might seem, inheritance and polymorphism aren't infallible. You might sometimes face the infamous diamond problem of multiple inheritances or the fragile base class problem, to name a few.

Moreover, an excessive use of polymorphism can make the code harder to understand and debug. Time to turn to SOLID principles, specifically the Liskov Substitution Principle, Interface Segregation, and Dependency Inversion Principle, to help mitigate such issues.

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