Kotlin String Templates

String templates let you embed variables and expressions directly inside a string. Instead of breaking a string apart and joining it with +, you write the variable name right inside the text using a $ sign.

Basic String Template

val name = "Sara"
println("Hello, $name!")   // Hello, Sara!

The $name part gets replaced by the actual value of name when the line runs.

Without vs With String Templates

Without templates (old way):
val city = "Paris"
val msg = "Welcome to " + city + "! Population: " + 2_000_000
─────────────────────────────────────────────────────────────

With string templates (Kotlin way):
val city = "Paris"
val msg = "Welcome to $city! Population: 2000000"

Much cleaner and easier to read.

Embedding Expressions with ${}

When you need to embed a calculation or a function call — not just a variable — use ${} with curly braces.

val price = 100
val tax = 18

println("Price: $price")
println("Tax: $tax")
println("Total: ${price + tax}")     // Total: 118
println("Tax rate: ${tax.toDouble() / price * 100}%")  // Tax rate: 18.0%

Diagram: How Template Resolution Works

val username = "Leo"
val score = 850

val message = "Player $username scored ${score * 2} points!"

Step 1: Find $username   → replace with "Leo"
Step 2: Find ${score * 2} → evaluate 850 * 2 = 1700, replace
Step 3: Result → "Player Leo scored 1700 points!"

Calling Functions Inside Templates

val word = "kotlin"

println("Original: $word")
println("Upper: ${word.uppercase()}")
println("Length: ${word.length}")
println("First char: ${word[0]}")

Output:

Original: kotlin
Upper: KOTLIN
Length: 6
First char: k

Using $ in a String (Literal Dollar Sign)

To print an actual dollar sign character without triggering a template, use \$:

val amount = 250
println("You owe \$$amount")   // You owe $250

Templates in Multiline Strings

val firstName = "Anjali"
val lastName = "Sharma"
val age = 30

val profile = """
    Name : $firstName $lastName
    Age  : $age
    Born : ${2024 - age}
""".trimIndent()

println(profile)

Output:

Name : Anjali Sharma
Age  : 30
Born : 1994

Practical Example: Invoice Generator

fun main() {
    val customer = "Raj Electronics"
    val item = "LED TV 55 inch"
    val qty = 3
    val unitPrice = 32000.0
    val taxRate = 0.12

    val subtotal = qty * unitPrice
    val tax = subtotal * taxRate
    val total = subtotal + tax

    println("""
        ─────────────────────────────
        INVOICE
        Customer : $customer
        Item     : $item
        Quantity : $qty
        Unit Price: ₹$unitPrice
        Subtotal : ₹$subtotal
        Tax (12%): ₹$tax
        Total    : ₹$total
        ─────────────────────────────
    """.trimIndent())
}

Output:

─────────────────────────────
INVOICE
Customer : Raj Electronics
Item     : LED TV 55 inch
Quantity : 3
Unit Price: ₹32000.0
Subtotal : ₹96000.0
Tax (12%): ₹11520.0
Total    : ₹107520.0
─────────────────────────────

String templates remove the need to concatenate strings manually. They make the code shorter and the output format obvious just from reading the string itself.