Kotlin vs Java for Mobile and Web Development

When starting a new project, choosing a programming language is one of the most critical things to consider. Your choice plays a vital role in your application’s efficiency, scalability, maintenance, and overall performance.

Two languages that stand out in web and mobile development are Kotlin and Java. They’re widely used, versatile, robust, object-oriented languages that can serve as a solid foundation for your development needs.

This article highlights the similarities and differences between Kotlin and Java, their benefits and limitations, and some use cases to help you decide which language to choose for your projects.

What Is Java?

Java is a high-level, object-oriented programming language (OOP). In other words, everything in Java is organized by classes and objects. It’s also platform-independent, meaning you can write your code once and run it on any platform with a Java Virtual Machine (JVM).

Its ability to handle large-scale workloads has made Java a reliable choice for web and application development. Many organizations, including Google, Uber, and Airbnb, use Java in their tech stacks.

Java boasts a prominent and engaging developer community that provides open-source projects and learning resources. By working with Java, you can access a broad selection of libraries, frameworks, and other tools the community maintains.

What Is Kotlin?

Kotlin is an open-source, modern, statically typed programming language initially designed to be compatible with a JVM. However, Kotlin has expanded its capabilities to support other environments, such as web browsers. It also embraces both functional and OOP concepts.

Kotlin addresses Java’s limitations, making it a more concise, expressive, and safe language. Kotlin is also interoperable with Java so you can use it with existing Java code and libraries.

In 2017, Google announced Kotlin as the official language for Android development, leading to the widespread adoption of Kotlin among Android developers.

A critical feature Kotlin provides is Kotlin/JS, which allows you to compile Kotlin code into JavaScript. This feature enables you to combine the unique features of Kotlin with popular JavaScript libraries for web development.

Kotlin and Java Compared

Now that you have a high-level overview of the two languages, this section looks at how Kotlin and Java differ from each other and their similarities.

Syntax and Language

Java is verbose. Since it doesn’t support type inference, you must indicate the data and return types of variables and methods. Additionally, Java code often resides in classes, leading to more boilerplate code.

The snippet below shows the lines of code needed to create a simple “Hello, world” program in Java:

public class HelloWorld {
  public static void main(String[] args) {
    System.out.println("Hello world");

Kotlin, on the other hand, is more concise. It eliminates much of the boilerplate present in Java by introducing features such as type inference, smart casts, data classes, and null safety.

The following snippet is the equivalent of the “Hello, world” program in Kotlin and demonstrates its concision compared to Java:

fun main() {
  println("Hello world")

In Kotlin, variables are non-nullable by default unless you explicitly mark them as nullable using the ? operator. By contrast, if you can assign null to any variable in Java, it makes it prone to null pointer exceptions.

Kotlin and Java handle concurrency differently. While Java provides Thread and Executor for concurrent tasks, Kotlin uses coroutines and suspending functions, allowing you to perform asynchronous tasks sequentially.

It’s also worth noting that, unlike Java, semicolons are optional in Kotlin. Kotlin also provides other distinctive features, such as sealed classes, singletons, inline functions, and functional programming.

Performance and Efficiency

Kotlin generally compiles into the same JVM bytecode as Java, so the difference in performance between both languages in production applications is usually negligible. However, Kotlin slightly outperforms Java in some areas due to its more concise syntax and modern features, such as inline functions.

Interoperability and Compatibility

As Java has a mature ecosystem of libraries and frameworks, it supports different databases, including Oracle, MySQL, and PostgreSQL. It also provides several frameworks for web development, like Spring, Jakarta Server Pages, formerly JavaServer Pages (JSP), and Jakarta Faces, formerly Jakarta Server Faces and JavaServer Faces (JSF).

Kotlin, on the other hand, is entirely interoperable with Java allowing you to call Java code from Kotlin and vice-versa. Consequently, you can integrate the abundant collection of Java libraries in your Kotlin projects.

Similarly, with Kotlin/JS, you can leverage various JavaScript frameworks and libraries, such as React.js and Vue.js for web development.