Kotlin vs Java: Which Is Best for Developing Android Apps?


Java has been the most popular programming language for Android app development since the launch of the mobile OS. From the beginning of Android mobile applications, developers have been using Java to offer Android app development services.

However, in May 2019, Google announced that Kotlin is the preferred programming language for Android applications in Google Play Store. And since then, Kotlin has become a sought-after language for Android programmers.

But looking at the popularity of Kotlin, one might think that is it better than Java for Android app development? Keep reading this article to solve the dilemma.

Introduction to Kotlin

Developed by JetBrains, Kotlin is an open-source programming language that can serve as a functional and object-oriented language. In addition, it is a statistically typed language for JavaScript and Java Virtual Machine (JVM). 

Kotlin differs from Java by its simplicity, clean code, and faster compilation. In addition, Kotlin can quickly compile code to bytecode and run on JVM, making it a platform-independent language.

Some stats about Kotlin

  • Kotlin is among the top five programming languages developers plan to adopt; the other four are Python, Go, TypeScript, and Rush.
  • In just three years of existence, Kotlin’s usage has increased to 7.8%
  • Kotlin powers Android apps of major tech giants like Google, Netflix, Amazon, Trello, etc.

Introduction to Java

Java is one of the oldest programming languages. It is a pure object-oriented language that found its way into the most sophisticated program – app development. The Open Handset Alliance (OHA) chose Java to be the primary language for Android app development.

Some notable features of Java

  • Multiple platform support: Java supports various platforms, meaning developers can start coding in Java and switch to Kotlin for Android app development.
  • Security: Many features like running programs into a virtual machine, not supporting explicit pointers, and bytecode verifier make Java the most secure and reliable programming language.
  • Garbage collector: Java uses a garbage collector to manage memory automatically, enabling developers to focus on other tasks than allocating and deallocating resources.

Similarities between Kotlin and Java

Kotlin and Java share many similarities, like:


Kotlin’s syntax is much similar to Java. So if you hire an Android developer who has mastery in Java, and your project requires Kotlin. Then they won’t have any hassle switching to a new language.

Collections library

Kotlin’s collections library is much similar to Java. And classes are also easy to convert, making it easy for those who want to try out this programming language.

Comprehensive comparison of Kotlin and Java

Extension functions

Developers switching from Java to Kotlin would find this function most useful because Kotlin makes it easy for developers to extend the functionalities of existing classes. And this is easy to do by adding a class name prefix to a function name.

Java, on the other hand, does not support extension functions. But you can extend the functionality of an existing class; only the process is time-consuming. In Java, you have to inherit the functions from the parent class to the child class. 

Code volume and speed of coding

Kotlin’s code volume will be much lesser than Java. And therefore, the language eases the developer’s efforts by minimising code errors. Thanks to the conciseness of Koltin code, enterprise Android app development has become much faster.

However, the coding speed of these two languages is almost similar. Kotlin may enable coders to type fewer codes. But when it comes to finding the solution for a given task, it requires more time. However, developers who have a good understanding of abstract thinking should choose Kotlin over Java.

Null safety

Null safety ensures null-dereference issues do not come up during the run time. The compiler automatically detects the null references and automatically fixes them during compile time. NullPointerException is a common problem in Java as it does not offer null safety.

However, Kotlin’s system uses a null safety feature. So, you will not encounter NullPointerExceptions error messages.


Program performance

Kotlin has additional features like a multithreading app that provides extra functionalities, making developers’ jobs easier. As a result, developers prefer Kotlin over Java. But these additions make Kotlin-based programs compile lower than Java-based programs.

Although this performance lag is negligible as both programming languages cover the program into bytecode before running on JVM, both programming languages are similar performance-wise.

Coroutine support

In Android OS, a long-running task may block the main thread, resulting in app crashes or unresponsiveness. To eliminate this problem, developers have developed concurrency design patterns such as coroutine.

Kotlin uses coroutine to hold the code execution and resume it when the situation is favourable. Kotlin coroutine also enables developers to run several tasks in one thread. But Java does not support coroutine features, so developers have to create multiple threads for handling lengthy operations. And that makes the program long.

Smart casts

If you choose to program in Java, you must manually inspect the variables’ type. And again, you have to cast the type of variable manually according to the operator.

Kotlin comes with smart casts, which handles all the casting checks. In addition, it has a smart compiler that removes redundant casts with stable values. Kotlin does this by tracking all the explicit casts and is-checks for immutable values.

Data classes

When you choose Java for Android app development, you have to set fields and variables to store data. You also need to create the constructor, getter and setter methods, toString(), equals(), and hashCode() functions.

But Kotlin simplifies these tasks with automation. You only have to add the keyword “data” in the class definition. Kotlin’s smart compiler will automatically create fields forgetter, setter, constructor, etc.


Wildcard code is a question mark that represents an unknown type. Java supports wildcards, and as a result, it handles the type-safety in Java code.

On the other hand, Kotlin does not support wildcards. But there is a wildcard alternative in Kotlin – type projections and declaration-site variance.

Operator overloading

Kotlin allows you to use various mathematical operators like addition, subtraction, and division. So you can quickly check equality or compare objects using symbols.

But, Java associates mathematical operators to specific data types, which restricts the use of symbols like Kotlin. For example, you can only use an addition symbol with string or numeric type for addition. Other data types can’t reuse this operator.


Kotlin or Java – Which is the best option for Android app development

Both languages offer exceptional benefits for Android app development services. However, there are scenarios when one language would be a better choice than another.

Kotlin is better for:

Kotlin is better for apps that must have excellent performance. For example, Kotlin is an ideal choice for apps that have to run smoothly on older Android versions or apps for photo editing. Kotlin is also a preferred language for apps that must maintain platform independence and be cross-compiled for multiple platforms apart from Android.

Java is better for:

Java is better for large applications that require lots of features and functionalities. Java is an ideal choice for large-scale applications that need to function across all the platforms, including Android, iOS, Linux, and Windows. Java’s mature library collection supports this kind of app development very well.

On a final note

Although Kotlin is the preferred language by Google Play Store, Java will remain a general-purpose language for Android and other app development. Therefore, it is a business owner’s and developer’s job to find the most suitable choice for their Android app project.

But if you find it difficult to decide, you can always contact us and get our free quick consultation regarding Android app development. Moreover, we offer you to hire an Android app developer who can contribute their expertise and knowledge to make your app development successful.

Does Kotlin have better performance than Java?

Kotlin is speedy, when it comes to performing incremental builds. But Java aids in developing a clean build for Android apps. Kotlin is a relatively new language, existing for the past 6 years, but more than 8% of developers are using this language and the number is increasing with the passing years.

If we make a complete comparison, we can find that Java is a faster programming language than Kotlin. A test reveals that on average, Java has upto 13% faster compilation speed (using gradle) than Kotlin. However, this difference in speed is only for complete builds.