How Major Metros Run on KMP
Shownotes
Every time you tap through a subway gate in New York City, you’re using Kotlin Multiplatform! In this episode, we sit down with Paweł Kwieciński from Masabi to explore how they brought a decade-old Java codebase to KMP, powering ticket validation across mobile apps, embedded devices, and backend systems for public transit agencies worldwide.
Resources:
- Masabi
- J2ObjC (Java to Objective-C translator)
- Google Workspace Migration to Kotlin
- Large Scale Changes with AI – Uber | Ty Smith
- KotlinX DateTime
- Ktor (Client & Server)
- Burst library (archived)
- Java ME (Micro Edition)
- Mbed TLS
- SQLDelight
- Compose Multiplatform
- JetBrains AI Assistant & Junie
Hosts:
Guest:
- Paweł Kwieciński
Timeline:
(0:00) Introduction
(1:12) What is Masabi?
(3:03) How does Kotlin fit into this?
(6:30) System architecture overview
(8:33) Embedded SDK and mobile apps
(10:33) Ticket inspectors and validators
(13:22) Offline operation
(16:29) The KMP decision
(24:42) Evaluating alternatives
(27:21) Planning the migration
(33:28) First lines of Kotlin
(43:45) Translating Java to Kotlin
(53:22) AI-assisted code translation
(56:39) Early AI era challenges
(1:05:01) Testing challenges
(1:08:22) KMP dependencies
(1:11:34) Domain-specific dependencies
(1:16:55) Java ME and C interop
(1:23:22) Backend-client sharing
(1:26:59) Current status
(1:31:48) Future plans: CMP
(1:36:26) Wrap-up