I’m a mobile app developer with 7+ years of experience building reliable, user-friendly applications for Android, iOS, and the web. I work mainly with Kotlin, Java, Swift, and PHP (Laravel), focusing on apps that are stable, scalable, and easy to maintain. I enjoy turning ideas into products that actually work well for users. From smooth UI and strong performance to clean backend logic, I care about building apps that feel simple to use but are solid under the hood. I also integrate AI-based features where they genuinely add value, such as smart search, recommendations, chat, or image/text recognition. I’ve worked across multiple domains and built features like payment gateways, scanners, digital signatures, real-time chat, push notifications, analytics, and social logins. I follow Material Design on Android and iOS to ensure a polished, native experience. 🔵 Skills & Experience 📱 Mobile Development ✅ Android: Kotlin, Java, Android SDK ✅ iOS: Swift, SwiftUI, UIKit ✅ KMM / cross-platform (when needed) 🌐 Web & Backend 🔹 PHP, Laravel, CodeIgniter, Node.js (APIs, admin panels, dashboards) 🔹 React.js, JavaScript, HTML, CSS 🔹 REST API design and integration 🤖 AI & Smart Features ✔ Recommendations & basic automation ✔ Chatbots & smart assistants ✔ OCR, scanning, image recognition ✔ ML Kit & TensorFlow Lite ✔ OpenAI & Google AI APIs 🛠 Tools & Integrations 🔹 Firebase (Auth, Firestore, Push, Analytics, Crashlytics) 🔹 Payments: Stripe, HyperPay, WorldPay 🔹 Git, Jira, Trello, Asana 💬 Click on “Message” and let’s connect. 📱 Have an app idea or need help improving an existing one? ✨ I’d love to discuss how we can bring your app to life with clean code and a great user experience. Let’s connect and build something that users actually enjoy using. 👍

I'm a programmer with 20+ years experience. I'm also an English/Croatian translator, writer, music composer and guitar player.

With over 5 years of dedicated experience in native Android development, I specialize in building high-performance, modern, and intelligent applications using Kotlin. My passion lies in transforming complex ideas into elegant, user-friendly mobile experiences. My portfolio on the Google Play Store showcases my ability to deliver full-featured apps from concept to launch, with a strong focus on cutting-edge technologies like Artificial Intelligence and 3D data visualization. MY CORE EXPERTISE INCLUDES: - Languages & Architecture: Kotlin (Expert), Java, MVVM/MVI, Clean Architecture - UI Development: Jetpack Compose, XML, Material Design - Asynchronous Programming: Coroutines & Flow - Dependency Injection: Hilt & Dagger - Networking & Data: Retrofit, Room, DataStore, JSON/RESTful APIs - Firebase Suite: Firestore, Authentication, Cloud Functions, Crashlytics - Advanced Features: AI/ML Model Integration, GPS & Location Services, 3D Rendering WHAT I BRING TO YOUR PROJECT: - AI-Powered App Development: Proven experience developing and integrating AI models to create smart, data-driven features, as seen in my "Medicine AI" and "DreamVault AI" apps. - Complex Feature Implementation: From real-time GPS tracking and 3D jump recreation ("Skydiving Tracker") to custom data storage and background services, I thrive on technical challenges. - Full-Cycle Development: I can lead a project from the initial idea and UI/UX implementation to final deployment and maintenance on the Google Play Store. - Collaborative Problem-Solver: Whether you need a dedicated developer to join your team, an expert to tackle a specific problem, or a consultant to guide your mobile strategy, I adapt to your needs to ensure project success. I am passionate about writing clean, scalable, and maintainable code. Let's connect to discuss how I can help you build your next successful Android application.

Java Spring Boot full stack developer specializing in fintech platforms and payment systems - Stripe, Plaid, and custom payment gateway integrations for enterprise and growing startups. I build secure, scalable backend systems that handle real money: wire transfers, EFT payments, subscription billing, and bank integrations. My work sits at the intersection of clean Java architecture and financial compliance: Spring Security, ISO 20022, PCI-aware design, and AWS serverless infrastructure. My core focus is payment gateway integrations: Stripe integration, Plaid integration, Interac, and custom EFT/Wire flows built on Spring Boot microservices designed for high-volume transaction processing. I also deliver full fintech SaaS platforms from MVP to production-ready architecture, AWS serverless infrastructure using Lambda, Fargate, SQS/SNS and Aurora PostgreSQL, and React frontends connected to financial backends. How I work: I start with a technical audit or business analysis to map exact requirements before writing a line of code. Every integration is documented, tested with JUnit, and handed over with internal team training so you can maintain and extend it in-house. Recent work: Delivered a full Interac payment integration for a UK-based fintech expanding into Canada, launched in 20 days using Java microservices and ISO 20022 standards with zero post-launch issues. Separately scaled a B2B payment SaaS platform to handle 10x transaction volume using AWS serverless architecture, cutting infrastructure costs by 30%. If you're building a fintech platform, integrating a payment gateway, or need a reliable Java backend partner for the long term, let's talk.

"I can unreservedly recommend Hussein for the development and support of Android apps. Over the last 2 years, Hussein has delivered amazing work, providing everything we need for Android, Android Auto, and Android Automotive. I have been impressed with how quickly he has supported complex challenges including Mapbox integration, Android Automotive, cloud-based comms, SignalR, and MQTT. 100% recommended." - Client, UK Transport Authority I'm an Android engineer with 4+ years across product companies and freelance work. My specialty is apps that talk to hardware (BLE devices, car head units, sensors), but my day job is production Android at scale, so you get both. 🛠️ WHAT I'VE ACTUALLY SHIPPED 🛒 E-commerce (current role at a software studio): - Cut checkout loading from 12-15s to 2-4s (83% faster) by reworking GraphQL queries, caching, and business logic - Led full migration from XML to Jetpack Compose with MVI, reviewing code and supervising the team - Integrated Payfort and Paymob payment gateways, built Loyalty and Gift Card systems with animated Compose Canvas UI 🚗 Android Automotive & Auto (2 years, UK Transport Authority, UK): - In-vehicle warning app running on a Polestar head unit, tested at Warwick University, covered in industry press (LCRIG) - Road safety and city safety apps: Mapbox, Google Maps, real-time location, MQTT, SignalR - Trained a TensorFlow Lite model with CameraX detecting vehicles for driver safety scoring 📡 BLE & Embedded (my own product, end to end): - Designed a BLE wearable from zero: custom 4-layer PCB (nRF52840, PMIC, capacitive touch), Zephyr firmware with OTA firmware updates over BLE, a Compose Multiplatform (KMP) companion app, and a Ktor backend behind it. I debug every layer: sensor, firmware, app, and server. 🔒 Security & hardened apps: - Built a 7-layer protection system for a client app: Talsec RASP, custom C++ native module for Frida detection, hardware-backed AES-256 with Android Keystore, SQLCipher, ProGuard/R8, string encryption, certificate pinning - Secure chat app: message and file encryption, voice recording, CameraX capture, root detection, USB debugging prevention. Cut its CPU usage by 30% and memory by 80% through profiling - System-level call/SMS handling with CallScreeningService inside Android's 5-second response window ☁️ Backend & self-hosted: - Ktor REST APIs with MySQL, Exposed, and Docker, sharing a Kotlin module between server and app for type-safe contracts - Device telemetry (GPS with 5-tier fallback, signal strength, battery), OTA APK updates, FCM remote commands and Remote Config - I run my own self-hosted infrastructure (Docker, Linux, reverse proxies, monitoring), so I'm comfortable deploying and maintaining what I build 📱 MY OWN PRODUCT - GPA Manager on Google Play: 16K+ downloads across 80+ universities, live Firebase backend Plus 20 completed Upwork contracts: in-app purchases and subscriptions, survivable background services, GPS tracking, offline data capture, SDK migrations. 🤝 HOW I WORK GitHub access from day one so the code is yours at every step. Honest estimates before we start, clear updates while we work, and two weeks of free support after delivery. I usually reply within a few hours. If you're building something with a device, a car screen, or just need an Android app done properly, message me. The first consultation is free: tell me about your project and I'll give you my honest take on the approach, effort, and risks before you spend anything.

I am a Senior Android Engineer with extensive experience delivering high-quality, production-ready mobile applications. My main focus is native Android development with Kotlin and Jetpack Compose, where I’ve built and maintained apps used by thousands to millions of users. In addition, I have successfully built and delivered cross-platform apps in Flutter and React Native, taking projects from concept and development through to production and market release. This allows me to tackle both native Android and cross-platform projects end-to-end, while maintaining deep expertise in Android. With 21,000+ hours on Upwork and top-rated feedback, I have proven the ability to deliver results efficiently, reliably, and to specification, whether it’s a long-term Android contract or a cross-platform project. If you’re looking for a senior mobile engineer who can own Android projects and also deliver cross-platform apps from scratch to market, I can help your app succeed quickly and efficiently.

Top Rated Plus | $200K+ Earned on Upwork | 100% Job Success | 10+ Years on Upwork I'm an Android Developer and Mobile App Developer with 12+ years of professional experience and a PhD in Computer Science. With $200K+ earned, 100% Job Success, and Top Rated Plus status on Upwork for 10+ years, I build production-ready Android and mobile applications that scale, not MVPs that fall apart under real user traffic. As an Android Developer, my core work covers native Android App Development in Kotlin and Java, full-lifecycle delivery from requirements and architecture through Google Play release, and backend integration with REST APIs, Firebase, AWS, and third-party services. I've shipped apps with 1M+ downloads. As a Mobile App Developer, I also deliver cross-platform solutions using React Native and Flutter when a project needs iOS and Android from a single codebase. As an Android Developer and Mobile App Developer, I've delivered across fintech, healthcare, logistics, social networking, sports, e-commerce, fitness, and entertainment. I also have extensive experience in healthcare and safety applications where data encryption, secure messaging, and compliance are non-negotiable. My architecture approach as an Android Developer is Clean Architecture with MVVM and MVP patterns, Kotlin Coroutines and Flow for async tasks, Hilt for dependency injection, and Jetpack Compose for modern UI. I use RxJava where legacy codebases require it and maintain CI/CD pipelines with Jenkins and TeamCity to keep releases reliable and predictable. As a Mobile App Developer and Kotlin developer, I take ownership of API planning with backend teams, code reviews, refactoring, and full technical documentation so the codebase remains maintainable long after delivery. I work as part of a team at Requestum, which means I can bring in backend, iOS, or QA specialists when a project needs more than one mobile app developer to ship on time. Clients typically work with me when they need: - an Android Developer to build a native Kotlin app from scratch to Google Play release - a Mobile App Developer to deliver iOS and Android from a single React Native or Flutter codebase - an Android App Developer to refactor, optimize, or extend an existing Kotlin or Java codebase - a Kotlin developer who understands Clean Architecture and can own the full technical roadmap - a mobile app developer with experience in fintech, healthcare, logistics, or social platforms If you need an Android Developer who ships production-grade apps and takes full technical ownership, let's talk. Main stack: Kotlin, Java, Android SDK, Jetpack Compose, Android Jetpack, Hilt, Kotlin Coroutines, RxJava, Retrofit, Firebase, AWS, Google Maps API, Stripe, React Native, Flutter, Room, Realm, Jenkins, Docker.

𝟴+ 𝗬𝗘𝗔𝗥𝗦 𝗢𝗙 𝗘𝗫𝗣𝗘𝗥𝗜𝗘𝗡𝗖𝗘 𝐢𝐧 𝐅𝐥𝐮𝐭𝐭𝐞𝐫, 𝐑𝐞𝐚𝐜𝐭 𝐍𝐚𝐭𝐢𝐯𝐞, 𝐒𝐰𝐢𝐟𝐭, 𝐊𝐨𝐭𝐥𝐢𝐧, 𝐅𝐢𝐫𝐞𝐛𝐚𝐬𝐞, 𝐆𝐫𝐚𝐩𝐡𝐐𝐋, 𝐀𝐏𝐈 𝐢𝐧𝐭𝐞𝐠𝐫𝐚𝐭𝐢𝐨𝐧𝐬, 𝐏𝐮𝐬𝐡 𝐍𝐨𝐭𝐢𝐟𝐢𝐜𝐚𝐭𝐢𝐨𝐧𝐬, 𝐈𝐧-𝐀𝐩𝐩 𝐏𝐮𝐫𝐜𝐡𝐚𝐬𝐞𝐬 I have 8+ years of experience working in different domains with diverse clients. Custom software solutions specific to business needs are my core expertise. Developed solutions for business domains like Real Estate, Banking and Finance, E-Commerce, Social Networking, live streaming, Sports, P2P payments, Wallet app, Fleet management, health, telemedicine, pdf scanning based, education, Shopping apps, Graphic designing, Fashion industry, study abroad & travel and many more. ◉ Technologies Exposure: - Native technologies:- Swift, Objective-C, Java, Kotlin, Android Studio. - Hybrid technologies:- React Native, Flutter, Flutter Flow, Dart, React. - Databases:- MySQL, MongoDB, MariaDB ◉ Domain experience:- - B2B, B2C flows - API Integrations of 3rd parties - Shipping workflows - Custom process workflows - Extensive reporting engine & dashboards - WebRTC (Custom)/ ZOOM/ Agora. ◉ Assist Retail Customers in:- - Mobile-based supply chain - Marketplace for Services & products - Online food ordering & delivery - Real estate domain - Business Automation - Logistics domain ◉ Compliance – More and more industries today are coming under the umbrella of compliance to comply with global norms, which allows them to compete globally. I have experience in implementation of:- -Healthcare Compliances - HIPAA -CGPA Compliances -Business risk advisory -Financial compliance -Environmental Guidelines ◉ E-commerce businesses may employ some or all of the following: -Online shopping websites for retail sales direct to consumers -Providing or participating in online marketplaces, which process third-party business-to-consumer or consumer-to-consumer sales -Business-to-business buying and selling -Gathering and using demographic data through web contacts and Social media -Business-to-business (B2B) Electronic data Interchange -Marketing to Prospective and established customers by E-mail or Fax (for example, with newsletters) -Engaging in Retail for launching new products and services -Online Financial Exchanges for Currency Exchanges or Trading Purposes Together, we can craft something that truly stands out. Let’s build something exceptional. Keywords: ------------- iOS & Android Developer | React Native | Flutter | Mobile App Development | Cross-Platform Apps | Dart | Swift | Kotlin | UI/UX Design | API Integration | Firebase | RESTful APIs | Git | App Store Deployment | Play Store Submission | Third-Party Libraries | Responsive Design | Testing & Debugging | Push Notifications | Performance Optimization | Mobile App Developer | iOS & Android Developer | iOS Mobile App Development | Android App Development | Flutter Mobile App Developer | React Native App Developer | Cross-Platform App Developer | Swift iOS Developer | Kotlin Android Developer | Native iOS & Android Development | Hybrid Mobile Apps Development | Flutter Dart Developer | React Native Cross-Platform Expert | Custom Mobile App Development | Mobile App UI/UX Design | Mobile API Integration | Backend APIs for Mobile Apps | iOS Swift App Development | Android Kotlin App Development | Mobile App Optimization | App Store Deployment (iOS & Android) | Mobile App Testing & Debugging | Firebase Integration for Mobile Apps | Mobile App Security & Performance | Push Notifications (Firebase, OneSignal) | Mobile App Maintenance & Support | Mobile App Monetization Strategies | Mobile Payment Integration | Cloud Sync & Mobile Data Storage | AI App | Chatbot |

What I Offer - Custom Mobile App Development for Android (Kotlin/Java), Flutter, and iOS (SwiftUI) - Clean Architecture & Scalable Codebases using MVVM, MVI, MVP, or Clean Architecture - Smooth API Integration with Retrofit, OkHttp, Ktor, and Firebase - Modern UI/UX Implementation using Jetpack Compose or traditional XML, based on designs from Figma or Sketch - App Optimization for performance, battery usage, and responsiveness - Agile Collaboration using tools like GitHub, Jira, ClickUp, Trello, and Slack Why Choose Me? - Proven Experience: 8+ years in Android native dev, including Kotlin, and Flutter for cross-platform. - Problem Solver: I don’t just write code — I solve problems and think about your product holistically. - On-Time & Within Budget: I respect deadlines and deliver quality without surprises. - Strong Communicator: Transparent, proactive, and always keeping you in the loop. - Client Satisfaction: Committed to long-term success and happy to support your app post-launch. Let’s Build Something Awesome Got an idea? Need help improving your existing app? Let’s collaborate and bring your mobile product to life. Click the “Invite” button or send me a message — I’m ready to get started!

Experienced mobile app developer with over 7 years experience in native Android apps. - Passionate about UI/UX design and accessibility - Bug-fixing expert - Experience on all kinds of apps, large and small - Good communicator, open and transparent