Technology advances very quickly these days, and there's always a new programming language or tool to learn.

You may have heard developers discussing the merits of and differences between two popular programming languages – Java and Kotlin.

So what's the difference between them? Which one should you learn? Well, you are in the right place, because that's what we'll talk about in this guide. I'll highlight the major differences between Java and Kotlin that you need to know in a very simple way.

Overview of Kotlin and Java

Kotlin and Java are two popular programming languages used to build software applications for a variety of platforms. While Java has been a dominant language in the software industry for over two decades, Kotlin is a newer language that has gained popularity in recent years due to its modern features and seamless interoperability with Java.

Java was first released in 1995 by Sun Microsystems, and it quickly became a popular language for building enterprise software applications. It is an object-oriented language with a strong emphasis on readability, maintainability, and portability.

Java is platform-independent, which means that it can be compiled and run on any platform that has a Java Virtual Machine (JVM).

Kotlin, on the other hand, was created by JetBrains in 2011 as an alternative to Java. It is a modern, statically-typed programming language that runs on the JVM, Android, and can be compiled to JavaScript.

Kotlin is designed to be concise, safe, and interoperable with Java, making it easy to integrate into existing Java projects.

In recent years, Kotlin has gained significant traction in the developer community, with many companies and organizations adopting it as their primary language for building software applications. But Java still remains a popular choice for building enterprise software, and it is likely to continue to be used for many years to come.

Differences Between Kotlin and Java

In this section, we will examine the key differences between these two programming languages.

Feature Kotlin Java
Syntax More concise and expressive syntax More verbose syntax
Null safety Built-in null safety features No built-in null safety features
Interoperability Seamless interoperability with Java Interoperable, but requires extra work
Extension functions Supports extension functions No support for extension functions
Lambdas More concise and expressive syntax for lambdas Lambdas are verbose and require more code
IDE support Strong IDE support in IntelliJ IDEA Strong IDE support in multiple IDEs
Performance Comparable performance to Java High performance, especially for large-scale applications
Learning curve Can have a steeper learning curve for those familiar with Java Fairly intuitive to learn
Community support Growing community with increasing resources Large and established community with a wealth of resources
Build tools Uses Gradle as the default build tool Uses Maven as the default build tool

It's important to note that this is not an exhaustive list, and there are other differences between Kotlin and Java depending on your specific use case. But this table provides some of the key differences between the two technologies.

Code examples of differences between Kotlin and Java

To write a Lambda Expression in Kotlin looks like this:

val list = listOf(1, 2, 3, 4, 5)
val evenNumbers = list.filter { it % 2 == 0 }

But in Java, it is much more verbose:

List<Integer> list = Arrays.asList(1, 2, 3, 4, 5);
List<Integer> evenNumbers =
                                 .filter(n -> n % 2 == 0)

Another practical example is using Extension Functions.

Kotlin allows you to add new functions to existing classes using extension functions:

fun String.isPalindrome(): Boolean {
    return this == this.reversed()

In Java, you cannot define extension functions. Instead, you can create utility classes with static methods:

public class StringUtils {
    public static boolean isPalindrome(String str) {
        return str.equals(new StringBuilder(str).reverse().toString());

Use Cases for Kotlin and Java

Both Kotlin and Java have their own unique use cases and when it is most suitable to use either of them.

When to use Kotlin:

  • Android app development: Kotlin is the recommended language for developing Android apps by Google. It offers features like null safety, concise code, and better readability, making it easier to build and maintain Android applications.
  • Web development: you can also use Kotlin for server-side development, and it can run on the Java Virtual Machine (JVM). This makes it a great choice for building web applications, especially when you need interoperability with Java.
  • Data science and machine learning: Kotlin has recently gained popularity in the field of data science and machine learning due to its ability to integrate well with Python libraries, such as TensorFlow and PyTorch.
  • Cross-platform development: you can use Kotlin to build applications for multiple platforms, including desktop, mobile, and web. This makes it an attractive choice for developers who want to build applications that can run on multiple devices.

When to use Java:

  • Enterprise application development: Java has been the go-to language for enterprise application development for decades. It has a vast ecosystem of libraries and frameworks you can use to build complex enterprise applications.
  • Legacy systems: Many legacy systems are built on Java, and migrating them to a new language may not be feasible or cost-effective. In these cases, Java is still the best choice for maintaining and updating these systems.
  • High-performance applications: Java is known for its performance and scalability, and it is often used for building high-performance applications that require high throughput and low latency.
  • Android app development: While Kotlin is now the recommended language for Android app development, Java is still a viable option. Many existing Android apps are built on Java, and you can still use it to build new applications for the platform.
  • Large-scale projects: Java's strong type system and emphasis on maintainability and scalability make it an ideal choice for large-scale projects. Its modular architecture also makes it easier to manage and maintain large codebases.
  • Desktop application development: you can use Java to build cross-platform desktop applications, making it a good choice for developers who want to build applications that can run on multiple operating systems.
  • Financial applications: Java's security features and stability make it a popular choice for building financial applications that require high levels of security and reliability.
  • Gaming: Java can also be used for game development, especially for browser-based games. It has a built-in 2D and 3D graphics engine that makes it easy to create games that run on multiple platforms.


In conclusion, Kotlin and Java are both powerful programming languages with their own unique strengths and use cases.

Kotlin is a relatively new language that offers features like null safety, concise code, and better readability, making it a great choice for Android app development, web development, data science, and cross-platform development.

Java, on the other hand, has been around for decades and is the go-to language for enterprise application development, legacy systems, high-performance applications, desktop application development, financial applications, and gaming.

If you're building an Android app, Kotlin is the recommended language by Google. If you're working on a legacy system or an enterprise application, Java is likely the best choice.

Finally, it's worth noting that Kotlin and Java are not mutually exclusive, and in many cases, they can be used together to achieve the best of both worlds.

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Happy Coding!