Java VS Kotlin

Most mobile app developers prefer one of the oldest programming languages out there – Java. For more than 10 years, this language was a king of Android apps, because this platform was also created with the help of Java. However, today the unquestionable leadership of Java is being challenged since a number of new promising languages occur.

One of such languages is Kotlin. Both of them are used to create applications and ensure the proper functioning of the user interface. While it doesn’t seem like Kotlin is going to replace Java completely, there are still some strong sides it can boast of. Should you switch from Java to Kotlin? Let’s compare Java and Kotlin and see which one suits your projects better.

Java: Pros and Cons

When it comes to Android app development, a major part of the developers choose Java. This can be explained by the fact that Android itself was written in Java. Java is an object-oriented programming language used for almost 20 years. It was developed by Sun Microsystems which is now the property of Oracle. Nowadays, it is considered to be the second most active language on GitHub.


  • Has a large and well-versed community, therefore – a number of great educational materials
  • Relatively simple and clear, which makes it easy to master
  • A language with a lot of features, regularly updated and open-source
  • Mostly used for Android, but works perfectly for cross-platform development
  • Has relatively high development speed
  • Applications created by means of Java are more lightweight than those that were made with the help of Kotlin
  • Has checked exceptions that improve error detecting and solving


  • Java requires a lot of memory and therefore can be slow sometimes
  • Not very suitable for Android API design because of a number of limitations
  • Requires a lot of manual work, which increases the number of potential errors

Kotlin: Pros and Cons

Kotlin is considered as Java’s alternative, which was initially created to add more functions to Java and solve the most crucial problems. Like Java, Kotlin has object-oriented features but is not limited to them, since it also has functional ones. The main purposes of this language are to ensure tooling support, interoperability, security, and legibility. It is matched with Java easily, so developers won’t have to learn it from the ground up if they already know Java. As for Java, it is used for Android app and desktop development.


  • Has user-friendly and understandable coding norms
  • Divides large apps into smaller layers and works faster and more efficiently with them
  • Doesn’t require any variable datatype specifications unlike Java
  • Uses a lot of function types and specialized language structures like lambda expressions
  • Allows developers to create extension functions easily, which are not available in Java
  • Provides a very simple and almost automated way of creating data classes


  • Has a small community of developers, and therefore – a lack of learning materials and professional assistance
  • Unlike Java, doesn’t have a function of checked exceptions, which may lead to errors
  • Compilation may take more time with Kotlin than with Java
  • Doesn’t have public fields that allow callers of an object change accordingly to representation

Java VS Kotlin: Comparison Table

Features/operations Java Kotlin
Managing threads For massive work, Java creates multiple threads, which may result in more bugs in the code Instead of threads, Kotlin is more likely to use lighter elements called coroutines, which require less memory
Extension function Java doesn’t have any extension functions Kotlin allows users to create extension function easily
Classes that hold data With Java, developers have to write, indicate and construct a lot of elements to create such classes Kotlin doesn’t require too much work when it comes to data classes; it is enough to include a class definition and data keyword only
Implicit conversions Java supports implicit conversions Kotlin doesn’t support implicit conversions
Null safety Every Java developer knows the pain connected with null safety; one can assign zero value to the objects when working with Java, but if he does, a NullPointerException will appear; this makes it harder to manage the coding process There are no null variables/objects in Kotlin; in most cases, your code will not work properly if you try to assign zero value to any object or variable
Smart casts When performing a certain operation with Java, we have to check the variables and define their type Kotlin checks the values and variables and performs necessary actions automatically
Functional programming Java is limited to object-oriented programming Kotlin combines both object-oriented and functional programming
Static members Java uses static members Kotlin doesn’t support static members


Obviously, both languages have their own restrictions and benefits, therefore the results of a Kotlin VS Java competition are debatable. While Kotlin covers some questions and solves problems that Java developers used to encounter, it doesn’t mean that Java will leave the development scene in the nearest future. Your language choice hardly depends on your preferences, aims, and strategies you use.

While switching from Java to Kotlin is easier than learning any other language, you will have to spend a month or two to do so. Still, you should think carefully if you really need it, because Kotlin will surely improve your performance in some ways, but won’t provide you with something absolutely different and new.

At the same time, a lot of emerging companies and start-ups prefer Kotlin to Java. This means that if you are thinking about making a career as a developer, you should take a careful look at Kotlin. Anyway, it is great to be aware of the latest trends and technologies as well as to experiment with them.

Who knows, maybe this will bring you significant benefits in the future! However, if you have no time to deal with complicated manuals, but need high-quality code to be written for your project, you can always rely on our Kotlin and Java development services