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Java vs Kotlin for Android App Development

Building an Android app is a popular option for many businesses considering creating their own mobile solution. That’s because Android is the most used smartphone operating system worldwide with over 2.5 bln active users in more than 190 countries in 2022.

While Android development is a clear choice for many, the debate on whether to build apps using Java or Kotlin continues unabated. Both programming languages work great for developing high performing, effective, and feature-packed Android apps. In this article, we’ll compare Java vs Kotlin and find out why these two programming languages raise so much debate in the Android app development circles.

Kotlin vs Java: Comparison

For a long time, Java was the most widely used programming language for building Android apps. Android developers still prefer using Java for its simple portability, platform independence, great development environment, easiness to learn, and large set of libraries of any kind.

In 2011, the JetBrains company considered all the Java advantages and drawbacks as well as the best aspects of other programming languages such as JavaScript, Pascal, TypeScript, Go, Scala, C++, C#, Rust, and many others, and created an alternative to Java – Kotlin. By 2019 Kotlin had already developed into a robust and stable programming language and Google claimed it to be a preferred option for Android development.

Why has Kotlin become Google’s choice and is it still worth developing Android apps in Java? To answer this question, let’s compare Java and Kotlin by various parameters.

Java and Kotlin Main Features

The main Java advantage is that it’s platform-independent. It means that it can run on any device that supports the JVM (Java Virtual Machine). Above all, Java is highly secure due to the use of a public key, encryption-based authentication, and its own illegal code-checking system.

With Java, software developers can identify code errors during the compilation time and eliminate error-prone states. Java has an extensive set of ready-made solutions and frameworks for faster development and issue solving.

One of the main reasons to choose Kotlin for Android development is that it shortens code length by up to 20% in comparison to Java. This makes Kotlin-based apps more efficient and less bug-prone.

Kotlin is a versatile programming language that can operate on any platform. That’s because it is compiled in bytecode and runs on JVM just like Java. Due to the use of JVM, Kotlin can be easily executed in Java and vice versa. This way, software developers can add as much Kotlin to Java and as much Java to Kotlin as they want and the developed app will run perfectly.

Ease of Use

Java is a basic programming language many developers start learning to code with. It has a flat learning curve and is easy to understand, yet, it can be quite challenging to read. Contrary to Java, Kotlin requires a bit more effort to learn but once it’s written, it’s much simpler to understand for other mobile developers.

Let’s have a look at the same basic “Hello World!” program written in the two programming languages:

Ease of Use

Kotlin needed just two lines to execute the program whereas Java extends to five lines to perform the same action.


When running Kotlin or Java apps, their code is compiled to bytecode which is executed on the JVM. Therefore, it’s quite hard to compare how the two languages use memory as they’re quite similar to each other in this way.

Meanwhile, adding some extra features to Kotlin makes it a more functional programming language than Java. The number of features in Kotlin results in a bit slower compilation than simple Java with fewer features. Although these differences in speed are so insignificant that hardly it’ll be noticeable for the developed business software.


Kotlin and Java easily interoperate with each other, therefore, companies can use the two programming languages when developing their projects. However, Kotlin takes it one step further, and starting from Kotlin 1.4 release, it is also easily compatible with Apple’s Objective-C and Swift languages. This way, software developers can also use Objective-C/Swift frameworks and libraries in Kotlin code whereas Kotlin modules can be utilized in Objective-C/Swift code as well.


Kotlin is quickly growing in popularity, especially among young companies that build their mobile solutions from scratch. Nevertheless, Java doesn’t take a back seat in mobile development. There are many companies that have been developing their mobile apps in Java for many years.

Moreover, those developers who want to work with Kotlin successfully still should be well-versed in Java. But, why do they need Java? Here are just some examples. It can happen that while building their mobile apps in Kotlin, software developers will have to use a specific library that operates only with Java. Another example is when reading Kotlin documentation, software developers run into explanations such as “it works like in Java, you just need to modify it slightly”.

Community Support

Although Kotlin is a rather new programming language, it already has much-developed documentation. Yet, it’s still easier to find many more detailed tutorials for Java. It’s so, simply because Java has been used for a longer period of time.

Kotlin, in its turn, doesn’t show any slow-down in its growing popularity. It means that more and more software developers opt for Kotlin and contribute to the development of this programming language.

Key Differences Between Java and Kotlin

It’s clear that Kotlin won’t replace Java in the near future. But, what makes Kotlin a preferable choice for many mobile app development projects? It’s all in the programming language. Here is a list of the key reasons why numerous developers opt for Kotlin over Java.

  • Null Safety

NullPointerExceptions is a famous software developers’ headache in Java when a null value is attributed to variables and objects by default. As a result, if developers attempt to refer to an object with a null value, the NullPointerExceptions opens the exception and they have to handle it.

In Kotlin, no variables or objects obtain null values by default and if a developer wants to assign a null value, they should add a question mark to the variable.

  • Extension Functions

In Kotlin, developers can extend the functionality of the existing classes without using an inheritance from the class or the decorator design pattern. It means that while adding more functions to the existing app components, software developers don’t have to implement any changes to the source code. Also, by using extensions, developers reduce the number of classes necessary for app building and make the code less repetitive. This helps to make Kotlin code much simpler to read and easier to maintain.

In Java, the inheritance function isn’t available and mobile developers have to write a certain method first and then call it to perform the needed action.

  • Coroutines Support

Heavy app processes can load up a smartphone’s CPU and block task execution on Android. To prevent this situation, mobile developers use a Multithreading feature in Java.