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Free, hands-on developer tutorials for juniors and seniors: programming in Swift, Kotlin and Java, iOS, Android, Java backend, design patterns, coding interviews and system design.
Free · No sign-up · For juniors and seniors
Continue where you left off118
Tutorials
3
Languages: Swift, Kotlin, Java
163
Glossary terms
34
Interview questions
Your roadmap
From the first line to the offer
Pick the track you need, or follow it in order. Every tutorial works for juniors and seniors alike.
- 1
Master the language
Types, optionals, closures, generics and concurrency, side by side in Swift, Kotlin and Java.
0 of 15 - 2
Build for iOS
SwiftUI, state, navigation, networking and Swift Concurrency.
0 of 16 - 3
Build for Android
Jetpack Compose, lifecycle, coroutines, Flow and Room.
0 of 16 - 4
Build the backend
Spring Boot, REST APIs, JPA, transactions and security.
0 of 13 - 5
Write better code
SOLID, Gang of Four and mobile architecture patterns, with before-and-after refactors.
0 of 23 - 6
Ace the interview
Coding problem patterns, system design case studies and real interview questions.
0 of 16
One tutorial, four versions
Junior or senior. Five minutes or thirty.
Two switches at the top of every tutorial change what you read. Juniors get analogies and step-by-step examples; seniors skip the basics and go straight to internals and trade-offs. Your choice is remembered on every page.
Code comes in Swift, Kotlin and Java. Pick your language once and every example opens in it.
Junior · Quick
The core idea and one simple example. Five minutes.
Junior · Detailed
Step by step, with analogies, many examples and exercises.
Senior · Quick
A cheat sheet: key APIs, gotchas and a comparison table.
Senior · Detailed
Internals, trade-offs, performance and production stories.
Bites
Remember what you learned.
Every lesson you finish adds short review cards: flashcards, quick quizzes, spot-the-bug and this-or-that. A few minutes a day brings each one back right when you're about to forget it.
Open your reviewEverything in one place
Explore the library
Programming
The core ideas every developer uses, shown side by side in Swift, Kotlin and Java.
iOS Development
Build iPhone apps with Swift and SwiftUI: state, navigation, networking, concurrency, architecture and shipping to the App Store.
Android Development
Build Android apps with Kotlin and Jetpack Compose: lifecycle, state, coroutines, architecture and releasing on Google Play.
Java Backend
Server-side Java with Spring Boot: REST APIs, databases, transactions, security, testing and running in production.
Design Patterns
SOLID, the classic Gang of Four patterns and mobile architecture patterns, with real problems and code in Swift, Kotlin and Java.
Coding Interview
The problem patterns behind most coding interviews, with hints, solutions in Swift, Kotlin and Java, and complexity analysis.
System Design
Design systems that scale, from load balancers and caches to full case studies, including mobile system design.
Glossary
Every developer term explained in plain English, with real examples.
Interview Questions
Common iOS, Android, backend and general developer interview questions with model answers, what interviewers look for, and flashcards.