Kotlin Default Arguments
Making functions more flexible and convenient
⚙️ What are Default Arguments?
Default arguments allow functions to have preset values for parameters. When calling the function, you can skip these parameters, making functions more flexible and easier to use.
// Function with default arguments
fun greet(name: String = "World", greeting: String = "Hello") {
println("$greeting, $name!")
}
fun main() {
greet() // Uses both defaults
greet("Alice") // Uses default greeting
greet("Bob", "Hi") // Uses no defaults
}
Output:
Hello, World!
Hello, Alice!
Hi, Bob!
Default Arguments Benefits
Flexibility
Call functions with fewer arguments
fun connect(host: String = "localhost") {
println("Connecting to $host")
}Convenience
Avoid repetitive parameter passing
fun log(message: String, level: String = "INFO") {
println("[$level] $message")
}Cleaner Code
Reduce function overloading
fun createUser(name: String, age: Int = 18) {
println("User: $name, Age: $age")
}Customization
Override defaults when needed
fun format(text: String, uppercase: Boolean = false) {
if (uppercase) println(text.uppercase()) else println(text)
}🔹 Basic Default Arguments
Set default values using the assignment operator (=):
fun createProfile(
name: String,
age: Int = 25,
city: String = "Unknown",
isActive: Boolean = true
) {
println("Profile: $name, $age years old, from $city, active: $isActive")
}
fun main() {
createProfile("Alice") // Uses 3 defaults
createProfile("Bob", 30) // Uses 2 defaults
createProfile("Charlie", 35, "New York") // Uses 1 default
createProfile("Diana", 28, "London", false) // Uses no defaults
}Output:
Profile: Alice, 25 years old, from Unknown, active: true
Profile: Bob, 30 years old, from Unknown, active: true
Profile: Charlie, 35 years old, from New York, active: true
Profile: Diana, 28 years old, from London, active: false
🔹 Mixed Required and Default Parameters
You can mix required and default parameters:
fun sendEmail(
recipient: String, // Required
subject: String = "No Subject", // Default
body: String = "", // Default
priority: String = "Normal" // Default
) {
println("To: $recipient")
println("Subject: $subject")
println("Body: $body")
println("Priority: $priority")
println("---")
}
fun main() {
sendEmail("[email protected]")
sendEmail("[email protected]", "Meeting Tomorrow")
sendEmail("[email protected]", "Urgent", "Please call me", "High")
}Output:
Subject: No Subject
Body:
Priority: Normal
---
Subject: Meeting Tomorrow
Body:
Priority: Normal
---
Subject: Urgent
Body: Please call me
Priority: High
---
🔹 Default Arguments with Expressions
Default values can be expressions or function calls:
import java.time.LocalDateTime
fun logMessage(
message: String,
timestamp: String = LocalDateTime.now().toString(),
level: String = "INFO",
maxLength: Int = message.length * 2
) {
val truncated = if (message.length > maxLength) {
message.take(maxLength) + "..."
} else {
message
}
println("[$timestamp] [$level] $truncated")
}
fun main() {
logMessage("System started")
Thread.sleep(1000) // Wait 1 second
logMessage("User logged in", level = "DEBUG")
}Output:
[2024-01-15T10:30:45.123] [INFO] System started
[2024-01-15T10:30:46.124] [DEBUG] User logged in