Parameters with default values in Kotlin - Step-by-Step Execution

Concept Flow - Parameters with default values

Function call

↓

Check if argument provided?

No→Use default value

Yes↓

Assign argument to parameter

↓

Execute function body

↓

Return result or finish

When a function is called, Kotlin checks if each parameter has an argument. If not, it uses the default value. Then it runs the function with those values.

Execution Sample

Kotlin

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

greet()
greet("Alice")

This code defines a function with a default parameter and calls it once without and once with an argument.

Execution Table

Step	Function Call	Parameter 'name'	Action	Output
1	greet()	No argument	Use default "Friend"	Hello, Friend!
2	greet("Alice")	Argument "Alice"	Use argument	Hello, Alice!
3	End	-	-	No more calls

💡 All function calls completed

Variable Tracker

Variable	Start	After call 1	After call 2	Final
name	-	"Friend"	"Alice"	-

Key Moments - 2 Insights

Why does greet() print "Hello, Friend!" even though no argument is given?

Because in step 1 of the execution_table, no argument is passed, so Kotlin uses the default value "Friend" for the parameter 'name'.

What happens if we provide an argument like "Alice"?

As shown in step 2, the argument "Alice" replaces the default, so the function prints "Hello, Alice!".

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'name' during the first function call?

A null

B "Alice"

C "Friend"

D No value

💡 Hint

Check the 'Parameter name' column in row 1 of the execution_table.

At which step does the function use the argument instead of the default?

A Step 1

B Step 2

C Step 3

D Never

💡 Hint

Look at the 'Action' column in the execution_table for step 2.

If we call greet("Bob"), what will be printed?

A Hello, Bob!

B Hello, Alice!

C Hello, Friend!

D Error

💡 Hint

Based on the pattern in the execution_table, providing an argument replaces the default.

Concept Snapshot

fun functionName(param: Type = defaultValue) {
  // function body
}

- If argument missing, defaultValue is used.
- If argument given, it overrides default.
- Helps avoid overloads and simplifies calls.

Full Transcript

This visual trace shows how Kotlin functions handle parameters with default values. When the function greet is called without an argument, Kotlin uses the default value "Friend" for the parameter 'name' and prints "Hello, Friend!". When called with an argument like "Alice", it uses that argument instead and prints "Hello, Alice!". This feature lets you write simpler functions that work with or without some arguments.