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Kotlin Development

Android is the most popular opensource operating system in the world, and it's created by Google corporation.
Two languages are used for development, Java and Kotlin.
4xxi successfully uses both of them.
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Many popular Google Play apps already use Kotlin:
  • Slack
  • Pinterest
  • Foursquare
  • American Express
  • WordPress
  • Evernote
  • Trello

Why Kotlin?

  • Compatibility
    Kotlin is fully compatible with JDK 6, is supported in the Android Studio and compatible with the Android build system.
  • Productivity
    Apps written in Kotlin are more productive than Java apps.
  • Efficiency
    Kotlin allows to quicken the app development time and to reduce compilation time.
  • Easy to learn
    Java developers can easily use Kotlin. Java code can be easily translated into Kotlin, which helps a lot in the beginning.
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High-Quality Development

  • Expertise
    Our team has developed a few unique, complicated products, with no counterparts on the market.
  • Quality
    We use the best and most flexible high-quality libraries for app development.
  • Experience
    For many years we've been perfecting our code-writing skills working with the latest coding languages versions.
Out favourine libraries and technologies are:
  • Kotlin Android Extensions
  • Android components
  • Retrofit2
  • OkHttp
  • RxJava/RxAndroid
  • Dagger2
  • Moxy/Mosby
  • ButterKnife
  • Firebase
  • Realm
  • Room
  • SQLite


  • Clients in many countries entrust us with their projects:
    • Canada
    • Estonia
    • France
    • Germany
    • Poland
    • Russia
    • Switzerland
    • USA
    • United Kingdom
    • Singapore


High-quality products for our clients are the most important thing for us, and no award has ever been a goal.
But sometimes rewards feel good.