Understanding Kotlin Inheritance and Extensions

Kotlin, a modern programming language, offers two powerful concepts: inheritance and extensions. While both allow developers to build upon existing classes, they serve distinct purposes and have different use cases.

What is Kotlin Inheritance?

Inheritance, a fundamental concept in object-oriented programming (OOP), enables a class to inherit properties and behavior from another class. In Kotlin, inheritance is implemented using the open keyword, which allows a class to be inherited from. The inheriting class, also known as the child class or subclass, can access all protected fields and functions of the parent class.

open class Animal {
    fun sound() {
        println("The animal makes a sound")
    }
}

class Dog : Animal() {
    override fun sound() {
        println("The dog barks")
    }
}

What are Kotlin Extensions?

Extensions, a feature introduced in Kotlin, enable developers to add functionality to existing classes without inheriting from them. Extensions are resolved statically and can be called like regular methods. They provide a way to extend the functionality of classes without modifying their source code.

fun String.greet() {
    println("Hello, $this!")
}

val name = "John"
name.greet() // prints "Hello, John!"

Key Differences between Inheritance and Extensions

When to Use Each

Use inheritance when:

• Creating a hierarchy of related classes.
• Needing to override the behavior of a parent class.

Use extensions when:

• Adding functionality to an existing class without modifying its source code.
• Creating utility functions that can be used across multiple classes.