Classes (Object-Oriented Programming)

In this lesson you will learn the basics of object-oriented programming with Kotlin classes, so you can group data that shares the same characteristics. This is for anyone searching for "Kotlin class how to use".

class defines a class. Because Kotlin lets you write the constructor parameters straight after the class name, a class definition is far more concise than in Java.

The sample code defines the properties and the constructor together in the single line class Animal(val name: String, val sound: String), and builds a message in the speak() method. Notice how Animal("Dog", "Woof") creates an instance.

A common stumbling block for beginners is how different this is from a Java class definition. Declaring the fields, defining the constructor, and generating the getters all happen in one line, and that concision can be disorienting at first.

In real-world development there is also the even more convenient data class, which is used constantly in Android app development.

📖 Reference code

class Animal(val name: String, val sound: String) {
    fun speak(): String {
        return "${name} says \"${sound}\""
    }
}

fun main() {
    val dog = Animal("Dog", "Woof")
    println(dog.speak())
}

✍️ Your code

Type your code, then press "Run"

🧪 This site can't compile or run Kotlin directly, so it checks on the spot whether what you typed matches the reference code (scoring happens entirely in your browser — nothing is sent anywhere).