Kotlin — Strings

String basics

fun main() {
    val s = "Hello, World!"
    val raw = """Raw string
with newlines"""

    println(s.length)        // 13
    println(s[0])            // H
    println(s.substring(0, 5)) // Hello
    println(s.uppercase())   // HELLO, WORLD!
}

String templates

fun main() {
    val name = "Alice"
    val age = 30

    println("Name: $name")
    println("Age: ${age + 1}")
    println("Uppercase: ${name.uppercase()}")
    println("Length: ${name.length}")
}

String operations

fun main() {
    val s = "Hello, World!"

    println(s.contains("World"))    // true
    println(s.startsWith("Hello"))  // true
    println(s.endsWith("!"))        // true
    println(s.indexOf("World"))     // 7
    println(s.replace("World", "Kotlin")) // Hello, Kotlin!
    println(s.split(", "))          // [Hello, World!]
    println(s.trim())               // Hello, World!
}

StringBuilder

val sb = StringBuilder()
sb.append("Hello")
sb.append(" ")
sb.append("World")
val result = sb.toString()
println(result) // Hello World

Regex

fun main() {
    val regex = "\\d+".toRegex()
    val matches = regex.findAll("abc123def456")
    matches.forEach { println(it.value) } // 123 456

    println(regex.containsMatchIn("abc123")) // true
    println(regex.replace("abc123def456", "#")) // abc#def#
}

Mini Practice

Write Kotlin code that:

1. Uses string templates with expressions
2. Splits a CSV string and prints each field
3. Uses regex to find all numbers in a string
4. Builds a string with StringBuilder

Up Next

In the next lesson, you'll learn about If Else — conditional branching in Kotlin.