String Templates in Kotlin

Introduction

String Templates is a fundamental concept every Kotlin developer should understand. Strings appear in almost every program — user input, file paths, API responses, and UI labels. Kotlin’s standard library provides concise helpers for common text tasks.

String templates embed variables and expressions inside strings. In this tutorial you will learn the syntax, walk through a complete example program, study the sample output, and review best practices so you can apply the concept confidently in your own projects.

Definition

• String templates embed variables and expressions inside strings.
• Use $variable for simple values and ${expression} for expressions.
• Templates make output formatting simple and readable.

Syntax

println("Value is $num")
println("Sum is ${a + b}")

String Templates in Kotlin Example Program in Kotlin

fun main(args: Array<String>) {
    val name = "Kotlin"
    val version = 2
    println("Language: $name")
    println("Version: ${version + 0}")
}

Sample Output

Language: Kotlin
Version: 2

When to use

Use string functions when formatting output, validating user input, splitting CSV data, or building URLs and file paths.

How it works

1. The program starts with a main function — the entry point that runs when you execute the file.

2. val name = "Kotlin" assigns or updates a value used later in the program.

3. val version = 2 assigns or updates a value used later in the program.

4. The println("Language: $name") statement writes a line to the console — this produces part of the sample output below.

5. The println("Version: ${version + 0}") statement writes a line to the console — this produces part of the sample output below.

6. String templates embed variables and expressions inside strings.

7. Run the program in IntelliJ IDEA, Android Studio, or with the Kotlin command-line compiler (kotlinc / kotlin). Compare your console output with the sample output shown below.

Best Practices

• Prefer string templates ("Hello, $name") over concatenation for readability.
• Use trim(), isBlank(), and isEmpty() to validate user input consistently.
• Choose StringBuilder when building large strings inside loops.

Common Mistakes

• Calling substring with wrong end indices — prefer substringAfter / substringBefore helpers.
• Using == when case-insensitive comparison is needed — use equals(other, ignoreCase = true).
• Concatenating inside tight loops instead of using StringBuilder.

Key Points

• String templates embed variables and expressions inside strings.
• Use $variable for simple values and ${expression} for expressions.
• Templates make output formatting simple and readable.
• Test the example locally and verify the output matches the sample.
• Experiment by changing input values to see how behaviour changes.

Notes

• Semicolons at the end of statements are optional in Kotlin.