Language Elements

Data Types

Kotlin Classes

Kotlin Operators

Kotlin Constructors

Kotlin Null Safety

Extension Functions

Lambda Functions

Object Oriented Kotlin

Data Classes

Coroutines

Kotlin Collections

Kotlin Data Structures

Kotlin Algorithms

Delegation

Lateinit and Lazy Initialization

Kotlin Scope Functions

Kotlin Key Words

Kotlin Example Codes

Kotlin Interview Questions

• Kotlin Classes
  
  A class in Kotlin is a blueprint for creating objects. It can contain properties (data) and functions (behavior). Classes are defined with the class keyword and support a primary constructor in the class header plus optional secondary constructors.

  
  class Person(val name: String, var age: Int) {
      // properties and functions go here
  }
          



• Core OOP Principles in Kotlin
  
  Kotlin fully supports the four fundamental object-oriented principles:


• Abstraction
  
  Hiding implementation details and exposing only essential features. Achieved with abstract classes and interfaces.

  
  abstract class Shape {
      abstract fun draw() = println("Drawing...")
      abstract fun area(): Double
  }
          



• Encapsulation
  
  Bundling data and methods while controlling access through visibility modifiers:
  • public — visible everywhere (default)
  • private — visible only in the same file
  • protected — visible in the class and its subclasses
  • internal — visible within the same module


• Inheritance
  
  Kotlin classes are final by default. Use the open keyword to allow inheritance:

  
  open class Animal
  class Dog : Animal()
          

  A class can inherit from only one parent class (single inheritance).


• Polymorphism
  
  Same interface, different behavior:
  • Compile-time polymorphism — method overloading
  • Runtime polymorphism — method overriding with the override keyword

  
  open class Animal { open fun sound() = "..." }
  class Cat : Animal() { override fun sound() = "Meow" }