With the announcement at Google I/O 2017 that the Kotlin programming language will be officially supported as a first class citizen for the Android framework, there’s been a lot of talk around what Kotlin is and how it compares to Java. This post highlights the reasons why our development team at Shockoe feels that Kotlin is the wave of the future and why Android developers should start adopting it.

What is Kotlin?

Kotlin is a statically typed programming language that runs on the Java Virtual Machine (JVM). It’s a multi paradigm language that contains elements of object-oriented programming that you’d see in languages like Java and elements of functional programming like what you’d find in JavaScript.

Why should you start using Kotlin?

Here are our top three reasons why you should jump in:

#1 Easily integrated into your mobile stack

Kotlin code is compiled into the same bytecode that your regular Java programs are and uses the Java Virtual Machine (JVM) to execute that code.
This means that Kotlin still has access to all the same libraries and frameworks available to you in the Java world with the addition of those from the Kotlin standard library. This also allows Kotlin and Java code to run concurrently with one another. Java classes calling methods in Kotlin classes or libraries and vice versa. This can even be done in the same file. Take this example from a library that handles unit conversion:

fun celsiusToFahrenheit(value: Double): Int = Math.round(value * 1.8 + 32).toInt()

Here we have a function that takes a Double parameter and returns an Int. However, we want to use the java.lang.Math class to round as this feature doesn’t exist in Kotlin. So we round to the nearest place and call a method from the Kotlin Double class to convert the result into an Int.

This duality of execution allows developers to easily convert their existing Android projects from Java to Kotlin or to simply add new features written in Kotlin, without converting previously written code.

Additionally, Kotlin has an option to compile into JavaScript which is compatible with the standard JavaScript specifications like Asynchronous Module Definition (AMD), CommonJS, and Universal Model Definition (UMD). This allows developers to share code written in Kotlin to other environments like Node.js or even to cross platform environments like to Appcelerator’s Titanium framework.

#2 Multi-paradigm language

A lot of the developers from Shockoe come from multiple different backgrounds. Some started with Java and transitioned into writing JavaScript while others started with JavaScript and have since learned about other languages.

Kotlin adds a lot of functional features to the object-oriented nature of Java. I realize that Java 8/9 adds similar features but this post is specific to the Android platform.

These features coupled with improved/sugar syntax lead to a much more easily read codebase. I won’t go over all the features but some of the most prominent ones are higher order functions, null safety, better typing with type inference, and much less boilerplate code.

These features, in particular, allow a developer to write much cleaner code and a lot less of it. Here’s an example of some Java code to perform and common action – filtering a list:

 ArrayList getAllEvenValues(int[] values) {
    ArrayList filtered = new ArrayList<>();
    for (int i : values) {
       if (i % 2 == 0) {
          filtered.add(i);
       }
    }
    return filtered;
 }

This isn’t too terribly much but it can quickly spiral out of control as you start adding more complexity. The Kotlin equivalent would look like:

fun getAllEvenValues(values: List): List = list.filter { it % 2 == 0 }

Yep, that’s it. There are many more operators that can be appended to the end of that, for instance if you wanted to map the results to strings and return the string list you just make one minor change.

fun getAllEvenValues(values: List): List = list.filter { it % 2 == 0 }.map { it.toString() }

#3 Official Support From Google

No brainer here, right? However, the announcement from Google I/O 2017 is a huge deal for the language. In addition to the benefits of Kotlin over Java such as those detailed above, Kotlin will now have full support in Android Studio and within the Android ecosystem. JetBrains and Google are working together to continue to support the language into the foreseeable future.

Kotlin is by no means meant to replace Java. However, it will allow for better apps to be written using a much more modern and architected language that keeps developers in mind.

Conclusion

Now is a great time to jump into Kotlin and to start writing your Android apps with it. It will lead to better productivity for your mobile team, as they’ll be writing less code – which will be more readable and therefore easier to maintain.

Additionally, if you’re a multi-platform development team, the cross compilation into JavaScript is a great addition as you can easily create tools that work within frameworks for both languages.

Then there’s also the similarities between Kotlin and Swift as is highlighted here. This helps  bridge the gap between iOS and Android development teams.

Additional Resources

Official Kotlin Documentation

Sample Kotlin App

Kotlin Android (Layout) Extensions

Anko – Library with many Kotlin helper tools for Android

Kovenant – Promises for Kotlin