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Kotlin
Google's modern language for Android. Concise, safe, and a joy to write.
MasterCoding practice
Learn by writing real code
Practice course concepts in an editable Kotlin workspace with instant checks, progressive hints, reference solutions, and visual execution traces.
Solution.kt
fun textLength(value: Any): Int =
(value as? String)?.length ?: -1✓ Uses a safe cast✓ Handles null safely
121
Interactive challenges
98
Write-code exercises
39
Visual walkthroughs
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Open all 121 challengesKotlin · Phases 1–4
Choose a phase or open the full lab. Every phase follows the concepts and modules in the current Kotlin course.
0131 challenges
Modules 1–7
Foundations
Syntax · null safety · control flow · functions
Start Phase 10230 challenges
Modules 8–12
Functional Kotlin
Lambdas · pipelines · scope functions · extensions
Start Phase 20330 challenges
Modules 13–21
Object-Oriented Kotlin
Classes · inheritance · sealed models · OOP design
Start Phase 30430 challenges
Modules 22–25
Collections & Generics
Collections · sequences · variance · delegation
Start Phase 4All learning tracks
One practice home for every course
Kotlin practice is live. The same exercise format is ready to expand across every MasterCoding track.
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Java
The backbone of Android and enterprise software. Master OOP the right way.
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Bring the web to life, master the browser, and build full-stack applications with one language.
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Node.js
Build fast server-side applications, APIs, command-line tools, and production backends with JavaScript.
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PHP
Build secure, data-driven web applications with modern PHP, SQL, testing, and Laravel.
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Get the best from AI — from how a model reads your words to reasoning, structured output, RAG, tools & agents — taught with real prompts and the responses they produce.
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Python
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SQL
Query, model, secure, and optimize relational databases from first SELECT to production analytics.
Built for active learning
Write, check, understand, repeat.
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