Default Parameter Values

In this lesson you will learn how to give a Kotlin parameter a default value so callers can leave it out. This is for anyone searching for "Kotlin default parameter how to use".

Writing = value on a parameter sets a default that is used automatically when the caller omits that argument. Picture an order form where leaving a field blank gets you the usual house set.

The sample code defines fun greet(name: String = "Guest"), which handles both greet("Alice"), where a name is supplied, and greet(), where nothing is passed.

A common stumbling block for beginners is combining defaults with named arguments. When several parameters have defaults, pairing them with named arguments (greet(name = "Alice")) makes the call read much better.

In real-world development, letting callers omit arguments gives you a flexible function that serves both the simple case and the finely tuned one.

📖 Reference code

fun greet(name: String = "Guest") {
    println("Hello, ${name}!")
}

fun main() {
    greet("Alice")
    greet()
}

✍️ 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).