Calling Java from Kotlin seamlessly - Mini Project: Build & Apply

Calling Java from Kotlin seamlessly

📖 Scenario: You are building a simple app that uses a Java class to perform basic math operations. You want to call this Java code from Kotlin without any trouble.

🎯 Goal: Learn how to create a Java class and call its methods from Kotlin code smoothly.

📋 What You'll Learn

Create a Java class with a method to add two numbers

Create a Kotlin variable to hold two numbers

Call the Java method from Kotlin to add the numbers

Print the result in Kotlin

💡 Why This Matters

🌍 Real World

Many Android apps use both Java and Kotlin code. Knowing how to call Java from Kotlin helps you reuse existing Java libraries easily.

💼 Career

Understanding interoperability between Java and Kotlin is important for Android developers and backend developers working with JVM languages.

1

Create a Java class with an add method

Create a Java class called MathOperations with a public static method add that takes two int parameters named a and b and returns their sum.

Kotlin

// Your code here

Need a hint?

Remember to make the method static so you can call it without creating an object.

2

Create Kotlin variables for numbers

In Kotlin, create two val variables named num1 and num2 and assign them the values 10 and 20 respectively.

Kotlin

public class MathOperations {
    public static int add(int a, int b) {
        return a + b;
    }
}

fun main() {
    // Create val num1 and num2 with values 10 and 20
    // Your code here
}

Need a hint?

Use val to create variables that won't change.

3

Call the Java add method from Kotlin

In the main function, call the Java method MathOperations.add with num1 and num2 as arguments and store the result in a val named sum.

Kotlin

public class MathOperations {
    public static int add(int a, int b) {
        return a + b;
    }
}

fun main() {
    val num1 = 10
    val num2 = 20
    // Call MathOperations.add with num1 and num2 and store in sum
    // Your code here
}

Need a hint?

Call the Java method using the class name directly because it is static.

4

Print the sum result in Kotlin

Add a println statement in the main function to print the text "Sum is: " followed by the value of sum.

Kotlin

public class MathOperations {
    public static int add(int a, int b) {
        return a + b;
    }
}

fun main() {
    val num1 = 10
    val num2 = 20
    val sum = MathOperations.add(num1, num2)
    // Print "Sum is: " and sum
    // Your code here
}

Need a hint?

Use println with an f-string style to show the sum.