Calling Kotlin from Java

Introduction

Kotlin is a modern programming language that runs on the Java Virtual Machine (JVM). One of its strengths is its interoperability with Java, enabling developers to use Kotlin code within Java applications seamlessly. This tutorial will guide you through the process of calling Kotlin code from Java, complete with explanations and examples.

Setting Up Your Environment

To get started, ensure you have the following installed:

• Java Development Kit (JDK)
• Kotlin Compiler
• An IDE such as IntelliJ IDEA or Eclipse with Kotlin plugin

Create a new project in your IDE and ensure that it supports both Java and Kotlin.

Creating a Kotlin Class

Let's create a simple Kotlin class with a method that we will call from Java. Create a file named Greeting.kt and add the following code:

class Greeting {
    fun greet(name: String): String {
        return "Hello, $name!"
    }
}
                

In this example, the Greeting class contains a method greet that takes a String parameter and returns a greeting message.

Calling Kotlin from Java

Now that we have our Kotlin class, we can call it from Java. Create a file named Main.java and add the following code:

public class Main {
    public static void main(String[] args) {
        Greeting greeting = new Greeting();
        String message = greeting.greet("World");
        System.out.println(message);
    }
}
                

Here, we create an instance of the Greeting class and call the greet method, passing in "World" as an argument. The result is then printed to the console.

Compiling and Running the Code

To compile and run your code, follow these steps:

1. Compile the Kotlin file:
kotlinc Greeting.kt -d Greeting.jar
2. Compile the Java file:
javac -cp Greeting.jar Main.java
3. Run the Java program:
java -cp .:Greeting.jar Main

After running these commands, you should see the following output:

Hello, World!

Conclusion

In this tutorial, you learned how to call Kotlin code from Java. Kotlin's seamless interoperability with Java allows developers to gradually migrate to Kotlin or utilize Kotlin's features in existing Java projects. By following the examples provided, you can start leveraging Kotlin in your Java applications.