How to Call a Kotlin Class from Java in Android

Have you ever come across the situation where you need to call a Kotlin class from Java in Android? Well, it can be a bit tricky at times, especially if you are new to the Android development world. In this article, we will guide you through the process of calling a Kotlin class from Java in Android.

Before we dive deep into the topic, let’s have a quick look at what Kotlin and Java are and why they are used in Android development.

What is Kotlin?

Kotlin is a modern, open-source programming language that runs on the Java Virtual Machine (JVM). It was introduced in 2011 and was developed by JetBrains, the same company that created IntelliJ IDEA, the most popular Java IDE. Kotlin is designed to be a better alternative to Java, with concise syntax, null safety, and improved performance.

What is Java?

Java is an object-oriented programming language that was introduced in 1995 by Sun Microsystems (now acquired by Oracle Corporation). It is still one of the most popular programming languages used in Android development and is known for its ease of use, platform independence, and security.

Why use Kotlin in Android development?

Kotlin has become more popular in recent years, and it has a lot of great features that make it a better choice over Java. Here are some of the reasons why you should consider using Kotlin in your Android development projects:

  • Concise syntax: Kotlin has a concise and expressive syntax that makes it easier to read and write than Java. It reduces the amount of boilerplate code and makes your code more readable and maintainable.

  • Null safety: Kotlin has null safety features that prevent null pointer exceptions, a common problem in Java.

  • Interoperability: Kotlin is interoperable with Java, which means you can easily call Java code from Kotlin and vice versa.

  • Performance: Kotlin is designed to have better performance than Java, with features like inline functions and extension functions.

Now that you know the basics of Kotlin and Java let’s move on to the main topic of this article, which is how to call a Kotlin class from Java in Android.

Calling a Kotlin class from Java

First, let’s create a Kotlin class that we can call from Java. Open Android Studio and create a new Kotlin class named "HelloKotlin". Add the following code to the class:

class HelloKotlin {
    fun sayHello(name: String) {
        println("Hello, $name!")

This is a simple Kotlin class that has one function named "sayHello". The function takes a string argument called "name" and prints out a greeting message.

Now, let’s move on to calling this Kotlin class from Java.

Step 1: Declare a Kotlin object

In Kotlin, you can create a singleton object using the "object" keyword. This creates a class with a single instance that can be accessed from anywhere in your program.

To call a Kotlin class from Java, you need to declare a Kotlin object that contains the functions that you want to call.

Add the following code to your Kotlin file to create an object:

object KotlinObject {
    val helloKotlin = HelloKotlin()

    fun callHello(name: String) {

In this code, we have created a Kotlin object named "KotlinObject". Inside the object, we have created an instance of the "HelloKotlin" class named "helloKotlin". We have also created a function named "callHello" that takes a string argument called "name".

Inside the "callHello" function, we call the "sayHello" function on the "helloKotlin" instance. This is the function that we want to call from Java.

Step 2: Call the Kotlin function from Java

Now that we have declared our Kotlin object, we can call it from Java. Create a new Java class named "HelloJava" and add the following code:

public class HelloJava {
    public static void main(String[] args) {

In this code, we have created a Java class named "HelloJava". Inside the "main" function, we call the "callHello" function on the "KotlinObject" object.

And that’s it! You have successfully called a Kotlin function from Java in Android.


Calling a Kotlin class from Java in Android can seem daunting at first, but it’s actually not that difficult once you know the steps. In this article, we have shown you how to create a Kotlin object that can be called from Java. With this knowledge, you can now start using Kotlin in your Android development projects and take advantage of its many benefits. Happy coding!

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