Kotlin Fundamentals

Why Kotlin and Your First Program

Kotlin is the language Google recommends for Android. Meet it, run your first program in the browser and see why developers love how little code it needs.

val, var and Types

Kotlin separates values that never change from ones that do, and figures out most types for you. Learn the core types and safe conversions.

Strings, Templates and Reading Input

Build readable text with string templates, clean and format input, and read what the user types, safely, without crashing on bad input.

if, when and Loops

In Kotlin, if and when are expressions that return values — cleaner than Java's switch. Loop with ranges and collections.

Null Safety: Goodbye NullPointerException

The most common crash in Java apps is calling something on null. Kotlin's type system makes that mistake almost impossible — learn ?, ?., ?: and !!.

Functions, Default Arguments and Lambdas

Write concise functions with default and named arguments, single-expression bodies, extension functions and lambdas — used constantly in Android click handlers.

Extension Functions and Scope Functions

Add your own methods to existing types like String and Int, and use let, apply, also, run and with: the idioms you will see on every line of Android code.

Classes, Data Classes and Objects

Model your app's data. Kotlin gives you primary constructors, properties, data classes with free equals/toString/copy, and singleton objects.

Interfaces, Inheritance and Sealed Classes

Share behaviour with interfaces and open classes, and model screen states safely with sealed classes — a pattern used in almost every modern Android app.

Enums and Generics

Model fixed choices with enum classes, and write classes and functions that work with any type, safely. Both appear constantly in Android state handling.

Collections: List, Map and Powerful Operations

Kotlin's collection functions — map, filter, groupBy, sumOf, sortedBy — turn loops into one readable line. You will use them in every screen that shows a list.

Files and Dates

Keep data after the program closes by reading and writing files, and do date maths (due dates, ages, late fees) correctly with java.time.

Errors and Coroutines

Handle failures with try/catch and runCatching, and meet coroutines — Kotlin's way to do slow work (network, database) without freezing the app.

Flow: Streams of Values Over Time

A suspend function returns one value; a Flow delivers many, over time: live prices, download progress, search results as you type. Flow and StateFlow drive modern Android screens.

Packages, Gradle and Testing

Organise a real project into packages, add libraries with Gradle, and write automated tests with kotlin.test so you can change code without fear.

Mini Project: A Shop Cart in Kotlin

Combine data classes, collections, null safety and errors in one small program — the same model code you will plug into an Android app next.