Aleksandar Simic, Software Developer in Niš, Serbia
Aleksandar Simic

Software Developer in Niš, Serbia

Member since August 30, 2015
Aleksandar is a mobile engineer with nearly a decade of domain experience working for companies including Microsoft, Johnson & Johnson, and Nike. His portfolio is diverse, but he specializes in scalable, secure, robust solutions with custom UI in the health and fitness industry. He has applied his proactive stance as a lead engineer to witness startups funded on TechCrunch and see their user bases grow to tens of millions of users.
Aleksandar is now available for hire




Niš, Serbia



Preferred Environment

Android Studio, Git, Swift, Kotlin, Java

The most amazing...

...thing I've developed is a distributed system for PDF/DOC conversion which runs over a dozen different test types in parallel with the server in full control.


  • Lead Android Developer

    2017 - 2019
    Johnson & Johnson (via Toptal)
    • Led the development of multiple HIPAA compliant health-related Android applications written in Java and Kotlin by teams of various sizes.
    • Developed abstract and generic handling of use-cases whose structure, content, and UI elements are defined over the air.
    • Integrated the Android application with a Salesforce back-end.
    • Implemented architecture in Kotlin for out-of-the-box syncing down multiple Salesforce soups that had complex many-to-many relationships and dependencies by utilizing topological sort.
    • Integrated ZXing barcode scanning library into existing Android projects developed in Kotlin.
    • Maintained code quality and stability of the project throughout continuous CI/CD and peer review processes.
    • Mentored and supported younger members of the team.
    Technologies: Jira, Jenkins, Salesforce, EventBus, Model View Presenter (MVP), Model View Viewmodel (MVVM), Butterknife, Retrofit 2, Picasso, RxJava, Dagger 2, Kotlin, Java, Android
  • Lead Mobile Developer (Consultant)

    2017 - 2018
    • Stabilized existing iOS fitness application that utilized BLE technology by refactoring and introducing various patterns and libraries.
    • Implemented very complex multithreaded algorithms for communication with BLE devices while utilizing RxSwift that allowed the user to double the number of BLE devices used during a single session.
    • Dramatically improved the speed of BLE communication by almost 300%.
    • Stabilized BLE communication and increased success rates from 70% to nearly 100%.
    • Implemented the ability to use an abstract, contract-based style of communication with BLE devices that made it easy to add or remove support for different brands of sensors.
    • Developed a localized, on-device iOS server using Swifter that allows team members to easily mock API data and work in offline mode.
    • Developed a PoC Android application in Kotlin for multithreaded BLE communication with devices.
    • Led the development of an Android application and oversaw tasks and progress.
    Technologies: Jira, Kotlin, Android, Model View Viewmodel (MVVM), Realm, Alamofire, RxSwift, iOS, Swift
  • Lead Android Developer

    2015 - 2018
    Circle Medical (via Toptal)
    • Developed an entire HIPAA compliant Android application in Java with continuous improvements of all individual components.
    • Contributed to product development throughout regular meetings and analysis of features.
    • Implemented insurance card scanner, video calls, real-time chat, payment processor, and PDF reader using various SDKs (Acuant, ZoomUS, PubNub, Stripe, and MuPDF).
    • Established architecture and best practices for further development of the Android application.
    • Set up automation test architecture and CI/CD, and developed thousands of tests.
    • Maintained stability and supported both Android and iOS applications.
    Technologies: Stripe, Zoom, PubNub, SQL, SQLite, Mockito, Espresso, JUnit, Swift, iOS, Butterknife, Picasso, Dagger 2, Retrofit 2, RxJava, Java, Android
  • Android Team Lead (Consultant)

    2016 - 2017
    Infinite Leap
    • Led the development of Android applications and organized day-to-day activities of team members and their tasks.
    • Set up architecture for projects, tools, and organizational practices as well as enforced peer review within a team.
    • Oversaw the quality of the code, stability of application, and progress of the team.
    • Communicated requirements daily with the rest of the team.
    Technologies: Model View Presenter (MVP), Butterknife, Picasso, Retrofit, RxJava, Dagger 2, Java, Android
  • CEO | Android Team Lead

    2014 - 2015
    Singularity Software
    • Founded and managed a development outsourcing agency with 13 employees.
    • Led a team of Android engineers that developed 15 applications in Java and PhoneGap.
    • Developed in a Java enterprise-level Android application, for the oil industry that generates its UI and use-cases based on custom instructions from a REST API.
    • Refactored, improved, and stabilized My Diet Coach by introducing material design, MVP architectural patterns, repository patterns, unit tests, and new features that allowed for the successful scale of its user base to more than 10 million users.
    • Enforced usage of various open source libraries, CI/CD services, automation tests, and APIs that improved overall quality of projects.
    • Created tools and libraries for faster development, such as an image resizer for Android's drawables.
    • Utilized sensors on Android, such as NFC and Bluetooth.
    Technologies: Amazon Web Services (AWS), Parse, Fabric, Travis CI, Picasso, RxJava, Butterknife, Retrofit, PhoneGap, Java, Android
  • Android Developer

    2014 - 2014
    Scopic Software
    • Worked on half a dozen Android applications in Java and PhoneGap, relying heavily on communication with Google's and REST APIs.
    • Implemented an image analysis algorithm in Java that determines the user's heart rate based on a recording of a fingertip.
    • Enforced usage of best practices, such as MVC architectural pattern, Retrofit, Picasso, GreenDao, Espresso, and other open-source libraries.
    • Designed and developed a set of internal Android libraries and code generators.
    • Created various reusable custom UI controls for the Android system.
    Technologies: C++, PhoneGap, Java, Android
  • Software Developer Engineer in Testing

    2013 - 2014
    • Designed and developed the main, fully automated, generic, distributed test system in C#, executing millions of tests daily.
    • Integrated all existing test tools for PDF to DOC conversion into the main distributed test system, allowing developers to use it freely.
    • Improved existing test tools by adding parallel execution of tests that increased efficiency by an order of magnitude.
    • Created an automated test tool in C# for measuring the performance of PDF rendering engines.
    • Created an automated test tool in C# that measured the accuracy of vector image reconstruction after PDF to DOC conversion.
    • Defined and implemented automated test tools for full control of tested software and test scenario executions for it.
    Technologies: C++, C#
  • Android and Web Developer

    2011 - 2013
    • Implemented various beginner-level Android applications in Java.
    • Implemented various websites, pages, and systems in different technologies.
    • Integrated various third-party APIs (Twitter, Google+, Facebook, Google Maps, PayPal) as well as OAuth authorization whenever possible.
    Technologies: jQuery, JavaScript, JSON, CSS, HTML, PHP, Java, Android


  • Circle Medical (via Toptal)

    A primary healthcare practice that uses technology and artificial intelligence to deliver a better patient experience at a lower cost with better outcomes for patients. The practice raised over $12 million from various investors, including Y Combinator, Paul Buccheit (Gmail creator), Jawed Karim (YouTube Founder), A.Capital Ventures, and Collaborative Fund, and we were featured on Medium, Forbes, TechCrunch, and Venture Beat.

    Since early on in Circle Medical's history, I've worked as lead Android developer with complete ownership of the Java codebase and development lifecycle. I implemented all features, integrated it with various APIs and SDKs, and continuously improved architecture and overall codebase quality by applying Android's best practices, various patterns, and automation tests.

    Note: Application may not be accessible in countries outside the USA

  • Johnson & Johnson Health Partner (via Toptal)

    An end-to-end system used as a tool to support patients before and after their surgeries through a diverse set of lessons and action items that should be completed over time.

    The system consists of various components while the Android application was developed in Java and iOS in Swift. As a lead Android engineer, within a team of eight, I took part in the development of every feature as well as conducted code reviews, fixed bugs, improved architecture, and simplified the codebase.

  • Nike Tech Book (via Toptal)

    An end-to-end system that showcased new upcoming seasonal Nike's clothes and sneaker boots, with Android and iOS clients developed in Java and Swift. Featured in Mashable and in "Top Developers" section on Google Play.

    As part of the Android team, I developed a large number of custom UI controls, animations, and frameworks for it, handling complex user interaction, big file system handling, and various optimizations.

    Note: Android and iOS applications are not accessible anymore through the stores.

  • My Diet Coach

    A weight loss and tracker mobile application that helps users to make healthy lifestyle changes and motivates them to continue doing so, developed in Java for Android and Swift for iOS.

    During the course of two years, as lead Android developer, I've developed multiple new features, such as the food diary and avatar customization, introduction of material design, code refactoring, and continuous improvement to the codebase as the user base grew to over 10 million users.

  • Beyond Pulse

    A coaching diagnostic tool that provides teams with player's key health indicators, measurements from BLE sensors and its interpretation that can help improve individual's performance and training.

    As a lead iOS developer, besides adding new features, I've refactored the existing application in Swift, introducing MVVM architectural pattern as well as RxSwift, Realm, and repository pattern. This led toward significant improvements in scalability and speed of BLE communication, smoother UX, and overall stability of the application.

  • PDF to DOC Test System

    A distributed system for conducting prioritized automation tests and report generation, that allows developers to easily integrate any test tool in it and to perform those tests when needed, thus removing existing dependencies between engineers and test engineers. I've developed and designed the entire system in C# and integrated all existing test tools for PDF to DOC conversion.

    The entire system supports saving and restoring state; detection of number of workers online; priorities of different tests; conducting daily millions of tests in multithreaded fashion; automatic generation and emailing of test results, asserts, and performance to the developer who requested the test; and optimizing bucket size based on workers' CPU speed, number of available cores, overload, etc. Tests were doing comparison tests, stability and rendering checks, and more.

  • Plickers (via Toptal)

    A mobile and web application that helps teachers to manage and conduct tests for their students. Its main key lies within image processing algorithms that parse responses and real-time communication between mobile clients, websites, and projectors during tests as well as offline synchronization that ensures that assessment goes smoothly.

    I worked as an Android developer for a year, during which I've implemented completely new UI and UX designs, including custom animations and logic around it while supporting new features developed by core developers.

  • Epicuri

    A blend of POS and guest management cloud systems that simplifies managing a restaurant and improves the entire experience for the clients, with a back-end built in .NET and mobile applications in native languages. I've developed a set of custom UI controls for Android application, fixed various issues, and worked on a wide range of features.

    The system has two applications: one for clients and one for restaurant employees. Employees are able to handle reservations, process payments and tips, manage orders, generate and email invoices, and even draw floor plans. On the other side, the client is able to search for nearby places, make reservations, order food, tip waiters, and rate their experience.

  • FitzApp

    A fitness mobile application that allows users to buy and track different workout programs over time, developed for Android and iOS platforms. I led a team of five Android engineers during the development of the initial release, where my primary responsibilities were to design an architecture, plan sprints, track development progress, mentor developers, conduct meetings, do code reviews, and constantly improve the development process.

    Note: The application is available through the Google Play Store and can be found at:


  • Languages

    Java, Kotlin, Swift, PHP, HTML, CSS, JavaScript, C#, C++, SQL
  • Frameworks

    Dagger 2, .NET, JUnit, PhoneGap, Mockito
  • Libraries/APIs

    RxJava 2, Retrofit 2, Butterknife, Picasso, React, RxSwift, Alamofire, jQuery, Retrofit, RxJava, Fabric, PubNub, Stripe, LiveData, Android Architecture Components, Kingfisher
  • Tools

    Android Studio, Eclipse IDE, GitHub, Git, Travis CI, Zoom, Jira, Xcode, Sketch, Slack, Jenkins
  • Paradigms

    Model View Presenter (MVP), Model View Viewmodel (MVVM), Unit Testing, Test-driven Development (TDD), Model View Controller (MVC), Concurrent Programming
  • Platforms

    Android, iOS, Parse, Amazon Web Services (AWS), Firebase, Salesforce
  • Other

    Espresso, Front-end Development, Full-stack, Retrolambda, Regression Testing, Room, EventBus, OkHttp, Team Leadership
  • Storage

    SQLite, Realm, JSON, MySQL


  • Master's Degree in Software Engineering
    2007 - 2014
    Faculty of Electronic Engineering - Niš
  • Erasmus Mundus Exchange Program in Computer Science and Management
    2011 - 2012
    Wroclaw University of Technology - Wroclaw

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