Sung Hyun Back, Developer in Toronto, ON, Canada
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Sung Hyun Back

Android Developer

Toronto, ON, Canada

Toptal member since January 14, 2026

Expertise
XMLSoftware DevelopmentFull-stackJavaFirebaseREST APIKotlinDartFlutterBack-end DevelopersJUnitPHPMySQL
Bio

Sung Hyun is a senior Android engineer with 9+ years of experience delivering high‑quality apps and SDKs. His expertise spans Kotlin, Java, Jetpack Compose, Coroutines, and robust architectural patterns for building reliable, scalable Android products.

Portfolio

HP Inc
Java, Kotlin, Coroutines, SDKs, Jetpack Compose, Model View ViewModel (MVVM)...
Mapsted
Android App Development, Java, SDKs, Model View ViewModel (MVVM), Retrofit...
The ARIES Inc.
Android App Development, Kotlin, Coroutines, SDKs, Model View ViewModel (MVVM)...

Experience

  • Java - 9 years
  • Android App Development - 9 years
  • REST APIs - 7 years
  • Model View ViewModel (MVVM) - 7 years
  • Kotlin - 6 years
  • Coroutines - 6 years
  • SDKs - 6 years
  • Jetpack Compose - 4 years

Preferred Environment

Android App Development, Full-stack Development, Back-end Development

The most amazing...

...things I built are Android SDKs for a 100 million‑download-printing app, a top‑5 Amazon Android POS product, and a production‑ready full‑stack ordering system.

Work Experience

Software Applications Engineer

2021 - PRESENT
HP Inc
  • Developed the Android SDK for the Roam cloud printing platform, used in the HP app (100+ million downloads) and HP Roam to enable secure, anywhere-anytime mobile printing for HP+ and Enterprise users.
  • Developed core SDK features using Kotlin, coroutines, Retrofit, WorkManager, Bluetooth, and Android system components.
  • Optimized REST API interactions to improve reliability and performance in high‑volume environments.
  • Reduced crash rates from 25% to 7% through targeted debugging, refactoring, and improvements to internal libraries.
  • Built and maintained CI/CD pipelines in Azure DevOps, publishing SDK releases to GitHub and Nexus.
Technologies: Java, Kotlin, Coroutines, SDKs, Jetpack Compose, Model View ViewModel (MVVM), Retrofit, Firebase, XML, Android App Development, APIs, AI Tools, REST APIs

Intermediate Android Developer

2020 - 2021
Mapsted
  • Contributed to Mapsted’s indoor navigation platform used in malls, campuses, and museums, including Dubai Mall and Square One. Managed Android SDKs and supported multiple Android apps.
  • Developed Android features using Java, Retrofit, and Android components (services, BroadcastReceiver, and notifications) to enable real‑time indoor positioning and navigation.
  • Maintained and enhanced four Android SDK libraries, diagnosing and resolving issues to improve stability, performance, and client satisfaction.
  • Published SDK artifacts to JFrog Artifactory as part of structured release cycles, ensuring consistent and reliable delivery for internal and external developers.
  • Authored and maintained clear SDK documentation for Mapsted’s developer portal, improving onboarding efficiency and integration success for partner teams.
Technologies: Android App Development, Java, SDKs, Model View ViewModel (MVVM), Retrofit, Firebase, XML, JUnit, Mockito, Espresso, Crashlytics

Software Development Manager

2019 - 2021
The ARIES Inc.
  • Developed an Android POS system sold on Amazon and Costco Canada, surpassing 100+ units in four months and reaching the Top 5 in Amazon.ca’s POS category with strong customer reviews.
  • Designed Android application architecture and implemented key features using Java and Kotlin, MVVM, REST APIs, and modular components.
  • Built back-end services using Django, Python, and MySQL to support secure data storage, transaction workflows, and reliable communication with client applications.
  • Implemented unit and instrumented tests with JUnit and Robolectric to improve release stability and reduce production defects.
Technologies: Android App Development, Kotlin, Coroutines, SDKs, Model View ViewModel (MVVM), Retrofit, Firebase, XML, JUnit, Mockito, Espresso, Crashlytics, MySQL

Full-stack Software Developer

2016 - 2019
HEXA Electronics
  • Contributed to Restaurant Hub, an Android-based food‑ordering system used across restaurants, hotels, and resorts. Presented at the 2018 Restaurants Canada trade show and the HEXA CN Tower event, receiving strong interest from potential customers.
  • Built real‑time communication features using Java, TCP/IP, and Android components such as BroadcastReceiver and Bluetooth to enable seamless device‑to‑device interactions.
  • Designed UI layouts with XML and structured data payloads, improving consistency and reliability across multiple system modules.
  • Implemented JUnit test cases to strengthen functional accuracy and reduce regression issues prior to deployment.
  • Delivered three MVP Android apps (guest-facing, kitchen, and manager) for a hospitality food-ordering platform.
Technologies: Android App Development, Java, XML, JUnit, APIs

Experience

Android SDK Libraries and AI-driven Android App Development

https://github.com/sung2063/AndroidSliderViewsLibrary
I developed multiple open-source Android SDK libraries, including a carousel UI component and a Bluetooth communication module, along with sample apps that streamline developer integration. I also built a native Android application that integrates TensorFlow Lite to analyze skin-lesion images and identify potential cancer risks. I designed a complete on-device ML inference pipeline, optimized model performance for mobile, and delivered a smooth, intuitive user experience through efficient image preprocessing, camera handling, and clear result visualization.

Dining‑QR: Restaurant Ordering System (Full‑stack)

https://github.com/sung2063/dining-qr-ordering-frontend
Dining-QR is a restaurant ordering system that lets guests scan a QR code to browse the menu and place orders directly from their smartphones. It also includes a management dashboard for handling tables, staff, menu items, and real-time orders. The platform enhances the dining experience for customers and provides restaurant owners with practical tools and insights to manage operations more efficiently. The back end was built with Java, Spring Boot, and MySQL, and the front end uses React and TypeScript, with an optional Flutter mobile version.

Multi‑company Website Development (WordPress & Custom Web)

Developed and maintained websites for multiple companies, including Petroff Architecture (custom site development), Spectrum Mechanical (WordPress), and HEXA Electronics (WooCommerce). Worked across both front‑end and back‑end development using HTML, CSS, JavaScript, jQuery, PHP, and WordPress, and supported ongoing updates, content management, and site maintenance.

Education

2013 - 2017

Bachelor's Degree in Mathematics and Computer Science

York University - Toronto, ON, Canada

Certifications

APRIL 2023 - APRIL 2025

Google Play Store Listing Certificate

Google for Developers

APRIL 2021 - APRIL 2024

Associate Android Developer

Google for Developers

Skills

Libraries/APIs

Retrofit, REST APIs

Tools

Crashlytics

Languages

XML, Kotlin, Java, Dart, PHP

Paradigms

Model View ViewModel (MVVM)

Frameworks

Flutter, JUnit, Mockito, Espresso, TensorFlow Lite

Platforms

Firebase

Storage

MySQL

Other

SDKs, Android App Development, AI Tools, Jetpack Compose, Software Development, Coroutines, Full-stack Development, APIs, Applied Mathematics, Google Play Store, Back-end Development

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