11 parts · 11 chapters

Kotlin

A modern language on the JVM that keeps Java's ecosystem and removes much of its ceremony, the default for Android and a strong choice for backends. Measured on this course's laptop (Kotlin 2.4.20, JVM 26, kotlinx.coroutines 1.10.2): 100,000 coroutines each waiting one second completed in 1.4 to 1.7 seconds total, at roughly 355 bytes of heap each, and a failing child cancelled its sibling automatically.

Eleven parts in the shared language-course shape: basics; the type system and null safety; the JVM and Kotlin runtime; coroutines and structured concurrency; idioms; tooling and testing; Ktor end to end; Kotlin on Spring Boot; performance; what Kotlin is paired with in production (paired like Java: the Java course P10 stack); and the shared capstone, the ledger API in Kotlin.

Start reading · Part 0 Present as slides
basics · the type system and null safety · the JVM and Kotlin runtime · coroutines · idioms · tooling and testing · Ktor end to end · Kotlin on Spring · performance · in production: what Kotlin is paired with · capstoneintro → expert · backend and Android engineers
languageConcise syntax, data classes, sealed types, extension functions.
safetyNull safety in the type system.
concurrencyCoroutines, Flow and structured concurrency.
webKtor for lightweight services; Spring Boot for the full ecosystem.
platformJVM bytecode, Java interop, Kotlin Multiplatform.
capstoneThe ledger API with the shared acceptance tests.
00

Basics

First code
1 ch · ~8 min01

The Type System and Null Safety

Making illegal states unrepresentable
1 ch · ~8 min02

The JVM and Kotlin Runtime

What the compiler emits
1 ch · ~8 min03

Coroutines

Measured, then structured
1 ch · ~8 min04

Idioms

Domain errors as types
1 ch · ~8 min05

Tooling and Testing

Deterministic tests for async code
1 ch · ~8 min06

Ktor End to End

A transfers endpoint in Ktor
1 ch · ~8 min07

Kotlin on Spring

A Spring Boot service in Kotlin
1 ch · ~8 min08

Performance

Where Kotlin adds or removes cost
1 ch · ~8 min09

In Production: What Kotlin Is Paired With

Same JVM stack, Kotlin on top
1 ch · ~8 min10

Capstone: The Ledger API in Kotlin

Acceptance
1 ch · ~8 min
Part of the language trackShares its shape and capstone with the Java course (whose JVM and production parts apply directly), Go, Python, Rust, Rails and Elixir.