Kotlin annotations for Java callers (@JvmStatic, @JvmField) - Mini Project: Build & Apply

Using Kotlin Annotations for Java Callers (@JvmStatic, @JvmField)

📖 Scenario: You are creating a Kotlin class that will be used by Java code. To make the Kotlin code easier and more natural to call from Java, you will use special Kotlin annotations.These annotations help Java callers access Kotlin properties and functions as if they were regular Java static members or fields.

🎯 Goal: Build a Kotlin class with a companion object that uses @JvmStatic and @JvmField annotations so Java code can call the static function and access the field directly.

📋 What You'll Learn

Create a Kotlin class named Utils with a companion object

Inside the companion object, create a function greet that returns the string "Hello from Kotlin"

Annotate the greet function with @JvmStatic

Inside the companion object, create a constant string field VERSION with value "1.0"

Annotate the VERSION field with @JvmField

Print the result of calling Utils.greet() and the value of Utils.VERSION

💡 Why This Matters

🌍 Real World

Kotlin is often used in Android apps and backend services, but many projects still use Java. These annotations help Kotlin code work smoothly with existing Java code.

💼 Career

Understanding Kotlin-Java interoperability is important for Android developers and backend engineers working in mixed Kotlin and Java codebases.

1

Create the Kotlin class with a companion object

Create a Kotlin class called Utils with an empty companion object inside it.

Kotlin

class Utils {
    companion object {
        // Your code here
    }
}

Need a hint?

Remember, a companion object is like a static holder inside a Kotlin class.

2

Add a function with @JvmStatic annotation

Inside the companion object of Utils, create a function called greet that returns the string "Hello from Kotlin". Annotate this function with @JvmStatic.

Kotlin

class Utils {
    companion object {
        // Add @JvmStatic function greet here
    }
}

Need a hint?

Use @JvmStatic just before the function declaration inside the companion object.

3

Add a constant field with @JvmField annotation

Inside the companion object of Utils, create a constant string field called VERSION with the value "1.0". Annotate this field with @JvmField.

Kotlin

class Utils {
    companion object {
        @JvmStatic
        fun greet(): String {
            return "Hello from Kotlin"
        }
        // Add @JvmField VERSION here
    }
}

Need a hint?

Use @JvmField just before the val declaration inside the companion object.

4

Print the function call and field value

Write two println statements to print the result of calling Utils.greet() and the value of Utils.VERSION.

Kotlin

class Utils {
    companion object {
        @JvmStatic
        fun greet(): String {
            return "Hello from Kotlin"
        }

        @JvmField
        val VERSION: String = "1.0"
    }
}

// Print the greet message and version
// Your code here

Need a hint?

Call Utils.greet() and Utils.VERSION inside println to display their values.