Kotlin was designed by programmers from JetBrains (the guys behind integrated development environments) to add some modern features to Java that come in handy in mobile development. Kotlin is an open source, statically typed language based on Java Virtual Machine (JVM), but you can also compile it to JavaScript or Native for building code that can run on iOS. All it takes is installing the Kotlin Plugin and letting it configure your project.
Kotlin is now an official language on Android. It's expressive, concise, and powerful. Best of all, it's interoperable with our existing Android languages and runtime.
Cons of Kotlin
Rather steep learning curve when switching entire teams to Kotlin due to the language's concise syntax (both a blessing and a challenge.
Slower compilation speed than Java (though Kotlin was shown to beat Java in some cases.
Small developer community, which means limited learning resources and difficulty in finding answers to questions; one look at Stackoverflow will give you a rough idea – there are only around 8000 questions tagged with Kotlin against 1.37 million questions about Java.
Experienced Kotlin devs are still a rarity, so finding a mentor for your team might be tricky.
Android Studio’s auto-complete and compilation tends to run slower in comparison to pure Java project.