Calling Kotlin from Java - Mini Project: Build & Apply

Calling Kotlin from Java

📖 Scenario: You are working on a project where Kotlin and Java code need to work together. You want to call a Kotlin function from Java code.

🎯 Goal: Build a simple Kotlin function and call it from Java code, then print the result.

📋 What You'll Learn

Create a Kotlin file with a function named greet that takes a String parameter called name and returns a greeting message.

Create a Java class with a main method that calls the Kotlin greet function with the name "Alice".

Print the greeting message returned by the Kotlin function in the Java main method.

💡 Why This Matters

🌍 Real World

Many Android apps and JVM projects use both Kotlin and Java together. Knowing how to call Kotlin from Java helps you work on mixed codebases.

💼 Career

Understanding interoperability between Kotlin and Java is important for Android developers and backend developers working on JVM platforms.

1

Create Kotlin function greet

Create a Kotlin file named Greeting.kt and write a function called greet that takes a String parameter name and returns the string "Hello, " plus the name.

Kotlin

// Your code here

Need a hint?

Use a Kotlin function with a String parameter and return a greeting using string templates.

2

Create Java class with main method

Create a Java class named Main with a main method. Inside the method, declare a String variable named name and set it to "Alice".

Kotlin

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

// Your code here

Need a hint?

Write a Java class with a main method and declare a String variable.

3

Call Kotlin greet function from Java

In the Java main method, call the Kotlin function greet with the variable name and store the result in a String variable called message.

Kotlin

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

public class Main {
    public static void main(String[] args) {
        String name = "Alice";
        // Your code here
    }
}

Need a hint?

Use the Kotlin file name GreetingKt to call the greet function from Java.

4

Print the greeting message in Java

In the Java main method, print the message variable using System.out.println.

Kotlin

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

public class Main {
    public static void main(String[] args) {
        String name = "Alice";
        String message = GreetingKt.greet(name);
        // Your code here
    }
}

Need a hint?

Use System.out.println(message); to print the greeting.