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.

Use Cases for Kotlin and Java

You can use Kotlin and Java for a wide range of web and app development projects, as outlined in the following sections.

Java Use Cases

Java is a great option for the following use cases:

  • Legacy codebases — Developers often use Java to maintain legacy codebases, particularly enterprise and legacy Android applications.
  • Projects dependent on Java frameworks — Java has extensive libraries and frameworks that cut across different domains. You can integrate existing Java libraries to simplify development tasks.
  • Web development — Java offers several frameworks well-suited for web development, including JSF, JSP, and Spring.
  • Teams with extensive Java experience — Experienced teams can leverage their knowledge of Java to deliver high-quality applications quickly.

Kotlin Use Cases

The following use cases can benefit from using Kotlin:

  • New Android projects — Since Kotlin is the official recommended language for Android development, newer Android libraries like Jetpack Compose are only available there. So, consider using Kotlin for your new Android projects.
  • Web development: With Kotlin/JS, you can use Kotlin for your frontend web development projects and frameworks like Ktor and Spring for your backend development needs.
  • Concise and readable code — Kotlin is best suited for projects prioritizing clean, concise, and readable code due to its expressive syntax.
  • Use of modern language features — When developer productivity is a priority, Kotlin’s coding features, such as sound null safety, type inference, and data classes, make it your best choice.

Kotlin and Java in the Android and Web Ecosystem

Google’s first-class support of Kotlin for Android development has driven its widespread adoption. However, most of the Android SDK supports libraries and legacy applications that are still in Java so that you can use both languages in the same codebase for Android development.

More developers and organizations are embracing Kotlin with Ktor and Kotlin/JS for web development. Nonetheless, Java still has the upper hand in this area thanks to its extensive, stable, and mature ecosystem of libraries and frameworks tailored for web development.

How To Pick the Right Language: Kotlin or Java

Although Kotlin and Java share several similarities, they address different problems and have different strengths.

Choosing the most appropriate language is dependent on various factors, including:

  • Project requirements — Evaluating your project’s needs helps you determine which language aligns the best with your project’s goals. For example, consider the target platform of your application. Java may be better suited for enterprise server applications, whereas Kotlin might be the better choice for applications aimed at the Android OS.
  • Team skill set — Your team’s expertise is essential to consider. If your team is already experienced with Java, using Java might be a more prudent option as they can leverage this knowledge instead of learning a new language and syntax.
  • Language features — Assessing each language’s features helps you understand which language aligns better with your development needs. For instance, Kotlin supports null safety, which minimizes the risk of runtime errors, unlike Java, which is prone to null-related exceptions.
  • Language establishment and stability — Considering the level of establishment and stability of each language is vital, as these factors can significantly impact the success and longevity of your project. Java, with its decades-long history and proven reliability, is a solid choice for projects that demand a dependable platform. Kotlin, while innovative and agile, may introduce more frequent changes, making Java the preferred option for projects requiring long-term stability and reliable performance.

Summary

Both Kotlin and Java are good choices for web and application development. Java has excellent community support and many community-maintained libraries. However, Java is verbose and doesn’t support modern language features like null safety. Comparatively, Kotlin is much more concise, interoperable with Java, and has a steadily growing community.

Also, while Java has primitive types, which you must explicitly define for variables and methods, Kotlin treats them as objects and can infer data types. Kotlin also provides different syntactic sugar, such as data classes, extension functions, smart casts, and operator overloading, making code expressive and maintainable.

Ultimately, choosing which language to use depends on your project requirements, your team’s experience, and the language with the features that align best with your project’s goals. You can experiment with both languages to determine which one suits your needs.

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Marcia Ramos Kinsta

I'm the Editorial Team Lead at Kinsta. I'm a open source enthusiast and I love coding. With more than 7 years of technical writing and editing for the tech industry, I love collaborating with people to create clear and concise pieces of content and improve workflows.