Lotto24 - Android

At Lotto24 AG, I worked as a Senior Mobile Engineer responsible for modernizing and scaling the native Android app used by millions of lottery players in Germany. The project focused on refactoring legacy Java code, introducing Kotlin MVVM architecture, and adopting Jetpack Compose for a cleaner, more testable, and maintainable codebase. Over four years, I played a key role in improving performance, reducing technical debt, and building a foundation for faster, safer releases. The app handled high-volume traffic, in-app purchases, and critical user flows such as ticket creation, wallet management, and draw tracking—all with strong focus on compliance, reliability, and accessibility. Key Contributions: - Led the migration from XML-based UI to Jetpack Compose, covering ~80% of the screens and improving test reliability by 35%. - Refactored legacy Java modules into modular Kotlin MVVM components, reducing tech debt by ~70%. - Implemented concurrency using Coroutines and Flow, cutting network latency by ~30%. - Developed and maintained Android Widgets used by 200K+ weekly users, increasing engagement by ~18%. - Expanded unit test coverage to ~60% with JUnit and Mockito, improving release confidence and reducing regressions. - Optimized cold-start and runtime performance with Android Profiler and caching strategies. - Worked cross-functionally with Design, Backend, and QA to align UX flows with accessibility and compliance standards. - Ensured strong app security with token management, encryption, and secure persistence.