Interactive Kotlin practice

Turn Kotlin concepts into working code

Work through 121 challenges and 40 quiz questions across the first four phases. Write code, inspect focused checks, reveal progressive hints, step through visual traces, and use cumulative checkpoints to confirm what you retained.

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Foundations

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31 challenges shown

Module 1BeginnerPredict output

Trace your first program

Identify the entry point and execution order of a Kotlin program.

What is printed by this program?

mainprintlnexecution order

fun main() {
    println("Hello, Kotlin!")
    println(2 + 3)
}

Your output

Interactive visualizer

Execution timeline

Step 1 of 3

main()

The Kotlin runtime finds the program entry point.

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