Java vs. Kotlin: Which is the Better Option for Android App Development? | Concise Software

Java vs. Kotlin: Which is the Better Option for Android App Development?

So, you have a great idea for a mobile app? It’s time to look for the best technology stack. At this point, businesses usually look for the most suitable options for their projects. And one of the dilemmas they encounter is Java vs Kotlin.

While Java is a battle-tested technology that has been part of the tech scene for decades, Kotlin is a relatively new one. However, the Kotlin community is constantly growing. Note that in 2017, Google made Kotlin the second official language for Android app development – and in 2019, Kotlin became its main language. Since then, we have seen a dramatic rise in demand for this programming language from enterprises and developers alike. With Google’s recognition as the preferred language for Android app developers, Kotlin has taken the tech scene by storm.

Java vs Kotlin – which is better?

But does that make it the best technology choice for your app? How would you decide when facing the dilemma: Java vs Kotlin? Here’s everything you need to know about the differences between Java and Kotlin to make the best decision for your mobile app development project..

What is Kotlin?

Kotlin was created by developers from JetBrains who aimed to make the process of writing code better and more productive. It’s a general-purpose, open-source, statically-typed programming language for JavaScript and Java Virtual Machine (JVM). Its main advantage is that it introduces practical features to support Java interoperability, as well as concise expressions and abstractions together with improved syntax. It’s worth mentioning that it is also possible to write code in Kotlin/Native.

The central idea behind this technology is enabling mixed-language projects with Java. Another goal is accessibility on all platforms, and the release of Kotlin 1.3 showed improvements that advance this idea. Android developers can use one integrated development environment (IDE) to build apps with Kotlin for all platforms. Code reuse helps in scaling mobile apps, saving teams plenty of time and effort for addressing more challenging tasks.

Who uses Kotlin? Many enterprise leaders are migrating to Kotlin today or are at least planning to do so soon. Mobile apps from the major industry players like Netflix, Pinterest, Trello, Uber, Twitter, Airbnb, and Evernote have switched to Kotlin for their Android applications.

What is Java?

Released in 1995, Java is a statically-typed, object-oriented programming language available under the GNU General Public License. Most Java elements are accessible as open-source as well. Mobile developers use Java to build Android apps, but the language also comes in handy for web apps, embedded systems, server apps, and more.

For years, Java has been one of the most popular languages for software development. In recent years, it has emerged as a go-to technology for mobile development. That’s why Java allows building applications of all kinds.

Who uses Java for mobile development? For starters, Google used Java to build all the apps that come as part of Android smartphones.   

Kotlin vs Java – which one is better for your project?

Now that you know what Kotlin and Java are all about let’s have a look at the key differences between the two programming languages. You need to know all the differences in order to decide on the best option for you when facing the dilemma: Java vs Kotlin. 


This feature is Kotlin’s central goal and the main motivation behind the project of its creation. The creators of Kotlin wanted to use the existing knowledge to make all libraries available to Kotlin developers. Mobile developers can write modules in Kotlin that are interoperable with the existing Java code. The two languages can thus work together in one project easily.


One of the best things about Kotlin is that – contrary to Java – it offers concise expressions and abstractions. Kotlin makes a developer’s job easier and mitigates the risk of errors. And we all know that brevity also affects productivity, accelerating the software development process. Developing large projects in Kotlin is easier when every line of code can accomplish much more. Kotlin’s syntax is concise, but it’s also readable. It helps to avoid the risks that come with boilerplate code, which is often hard to read and leads to more bugs (and lots of time spent on trying to identify them).

Inherent null safety

If there’s one thing known for causing development mistakes in Android, it’s the NullPointerException. In Android, null represents the absence of a value. This sounds simple, but in reality, null can easily destroy an application. Kotlin addresses this problem by offering developing an inherent null safety. This saves teams a lot of time on writing extra code that works around the issue.

Performance and compile time

According to JetBrains (the creators of Kotlin), applications written in Kotlin run as fast as their equivalents built with Java. A similar bytecode structure is a reason behind this. Still, Kotlin offers support for inline functions, allowing developers to code using lambdas to run faster than the same code written in Java.

What about the compilation time-critical to developers’ productivity? For clean builds, Java compiles 10-15% faster than Kotlin. But for incremental compilations, Kotlin shows similar or even slightly better results than Java.

Checked exceptions

Java includes checked exceptions that are often unnecessary and cause empty hatch blocks. Moreover, nonexistent checked exceptions force developers to waste time weeding through the code to identify nonexistent exceptions. Kotlin removes that problem entirely, thereby minimizes the verbosity, improving type-safety, and saving development teams plenty of time.


Java has more than two decades of history on its back, so it’s only natural that it boasts an impressive community and a large number of successful projects. And the larger the community is, the higher the chances are that someone has already solved an issue your development team might be facing.

Even if Kotlin has gained a lot of traction, its community is still rather small when compared to Java’s. Since there are fewer people using Kotlin, the language doesn’t offer as many learning resources or tools. Sourcing Kotlin developers for a project might be more challenging than hiring Java developers, despite the steep learning curve of the language. However, since the language is heavily promoted by Google, it’s likely that more learning resources for Kotlin will emerge soon. Platforms like Udacity or Udemy are full of courses on Kotlin – and some of them are provided by Google. 

When to use Kotlin and Java?

Kotlin is an excellent technology for projects where time-to-market is important. In short, the language allows developers to solve more problems with fewer lines of code, but also read and modify code more efficiently.

Kotlin’s reduction of development time also comes with solid support for maintenance needs. Since there’s less code, developers can easily identify bugs – that’s also because Kotlin is very readable. As a result, you get to build a mobile app that experiences fewer crashes and system failures.

Still, let’s not forget that Kotlin has a bigger runtime size compared to Java – it means that apps larger than 1261 KB will become heavy. In general, Java supports the development of complex apps better than Kotlin. 

Read more: What is Flutter? Here is everything you should know

Remember about this when switching to Kotlin

Before switching to Kotlin, make sure that your team is ready for it. A new language always introduces a learning curve. After all, you’re aiming to rewrite and optimize your project, so it’s important to have a team ready to launch a learning process (and face many obstacles).

Also, consider how the switch will impact the existing architecture. Changing programming languages can cause a broad range of issues like deleting or merging particular classes or artifacts. Your product architecture might be damaged in the process. That’s why you need to ensure that your mobile architecture is expandable and can handle the switch.


Kotlin has, in a short time, become a viable development option for Android developers. Since this year it is the main language for Android App Development, Java is in the background, but is still used in many projects. And now facing the dilemma: Java vs Kotlin, which solutions is the best option for you?

Are you looking for expert advice on mobile development technologies? Reach out to us; we help companies across many sectors to make the most of Kotlin and Java for their mobile development projects.

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Justyna Kot

Project Manager & Business Analyst at Concise Software
Geek girl & coffee lover, Google Developers Launchpad Mentor , passionate about growth hacking, community building and Star Wars. Also Lead Organizer at Women Techmakers and GDG Rzeszów

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