James Cullimore
Freelance Android Developer
Niedereschach, Germany
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● Software / Application / Mobile Developer with experience in Java, Kotlin, Android, Web & Fullstack Development
● Creator of open source projects such as StreamingYorkie, blackforest-woodburnings.de & Lazy Shortcuts
● Developer of hansgrohe home, hansgrohe SmartExpert, farmerJoe & lexoffice
● Software development freelancer & technology hobbyist
● Android Instructor & Independent Writer
● Extensive knowledge in new technologies with keenness to learn more
● Married with 2 children
● MMA enthusiast
Area of Expertise
Topics
Wear OS Was Supposed to Be Easy, Right?
On paper, Wear OS development should feel like a natural extension of building Android apps. In practice, it often comes with hidden obstacles: UI redesigns, Play Store quirks, broken permission flows, missing APIs, and unexpected debugging challenges. In this roundtable, we’ll explore the realities of bringing apps to the wrist—from communication between phone and watch modules, to performance trade-offs, to custom UI workarounds. Join us to share experiences, frustrations, and lessons learned so the next wave of Wear OS apps can be a little smoother for everyone.
Kick-off questions:
> What has been your biggest surprise when moving from Android app development to Wear OS?
> How do you approach UI design differently for the wrist compared to the phone?
> What workarounds or hacks have you discovered for missing APIs or broken system flows on Wear OS?
> How do you test, debug, and deploy effectively when working with Wear OS hardware and the Play Store?
> Do you think Wear OS development will get easier over time, or are the constraints of the platform here to stay?
Building a Mobile Game Without an Engine, a Budget, or a Clue
Every developer dreams of building a game at some point. I did too. But with no time, no budget, and no prior game dev experience, it felt like something I’d never realistically pull off. This talk is the war story of how I proved myself wrong.
I'll walk you through how I turned an idea, a game I could play one-handed while walking my dog, into a working Kotlin-powered mobile game with in-app purchases, localization, and community traction. No Unity. No backend. No big budget. Just a roadmap, some creativity, and a lot of train rides for development.
We’ll look at how I made strategic tech decisions to avoid unnecessary complexity (like skipping an engine and going full Kotlin), how I kept costs near zero (using Fiverr, AI-generated assets, and open licensed music), and how I kept momentum alive with a clear MVP goal and low-pressure side project mindset.
If you’ve ever wanted to ship your own game but felt overwhelmed by the barrier to entry, this talk will give you a realistic, developer-first blueprint that starts with Kotlin and ends with a playable, publishable game.
Key Takeaways / Learning Points
- Why you don’t need a game engine to start building games as an Android dev.
- How to approach a side project with minimal time and budget and still ship.
- How to build a working MVP game in Kotlin, from graphics to gameplay.
- Tips for low-cost asset creation: AI tools, Fiverr, free music, and DIY design.
- How to start monetizing early (ads, IAPs) without a backend.
- Lessons from launching: app store assets, community traction, GDWC, and early feedback loops.
- The importance of scoping, accessibility, and localization from day one.
Contribute, Struggle, Adjust, Repeat: Finding Work-Life Balance as a Dev
In the ever-demanding world of Android development, maintaining a healthy work-life balance can feel like a juggling act—between code, clients, kids, partners, pets, and even the occasional whisky break. This roundtable discussion brings together personal experiences and practical insights on navigating the shift from full-time work to freelance, while keeping life and career in harmony. We'll explore how prioritizing relationships, health, and personal time has not only improved productivity but also fueled meaningful contributions to the Android community. From time management systems to the importance of community engagement, this discussion offers real talk and real tactics for developers seeking balance in both code and life.
Let's talk about:
How can developers successfully transition from full-time employment to freelance without losing work-life balance?
What role does personal well-being play in staying productive and focused in Android development?
In what ways can sharing knowledge and contributing to the Android community enhance both career growth and personal fulfillment?
What time management systems have worked—and failed—for developers, and how can they be adapted to reduce stress and promote sustainability?
How do breaks, hobbies, and family time actually make us better developers?
Faster Feedback: Cut Gradle Build and Pipeline Times in Half
Waiting on builds and pipelines wastes time and kills flow. In this talk, I’ll show how I cut both Gradle build times and CI pipeline durations by 50% on a production Android app, all without introducing new tools or rewriting existing code.
We’ll start with Gradle: I’ll break down which gradle.properties changes actually moved the needle, how updating to newer Java and Kotlin versions improved performance, and how a comparison between Groovy and Kotlin DSL surfaced potential future wins. You’ll get a practical look at what worked, what didn’t, and how to measure impact in your own project.
Then we’ll move to the CI pipeline: I’ll walk through how I restructured steps to increase parallel execution and reduce total pipeline time, not by adding complexity, but by thinking strategically about the build graph. These weren’t sweeping changes, just focused tweaks with big results.
If you’re looking for real-world ways to reduce build and pipeline friction, this talk will give you a toolkit of practical optimizations you can apply immediately.
Key Takeaways / Learning Points:
- Which gradle.properties settings directly impact build performance and why.
- How upgrading Java and Kotlin versions can unlock performance improvements with minimal effort.
- A comparison of Kotlin vs Groovy DSL for build scripts — and how Groovy may still offer speed advantages in some cases.
- How to redesign your CI pipeline to better utilize parallelism and minimize sequential slowdowns.
- A strategy for measuring and iterating on build/pipeline performance using simple metrics and real impact.
Hotfix Heaven: Why In-App Updates Are a MUST
Tired of waiting for vital updates to reach your users? In-App Updates are your secret weapon for delivering lightning-fast fixes, smooth API transitions, and enhanced security – all directly within your app.
This talk equips you to master In-App Updates for a thriving app:
- Become an update champion: Deliver instant fixes and keep users protected and satisfied.
- Navigate API migrations with ease: Ensure flawless user experience with seamless versioning and rollouts.
- Unlock developer efficiency: Streamline workflows, reduce friction, and empower users with immediate updates.
- UX in focus: We'll explore the impact of In-App Updates on user experience, including best practices for user buy-in.
- Strategic updates: Discover optimal update frequency to balance user engagement and retention while minimizing drop-off.
Gain real-world insights:
- Battle-tested strategies to supercharge both developer and user experience with In-App Updates.
- Hands-on implementation: Learn how to effortlessly set up In-App Updates on Android.
Who should attend?
- Android developers seeking faster, more efficient updates.
- Anyone passionate about boosting app security, stability, and user experience.
- Developers eager to learn practical implementation tactics for In-App Updates.
Join me and unlock the power of In-App Updates! Take your app development to the next level and become an update champion.
2025 | Berlin | droidcon Sessionize Event
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