Strings

Jun 23, 2026Trushi Jasani

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Strings

Creating Strings

fun main() {
    val name: String = "Kotlin"
    val greeting = "Hello, $name!"

    // Multiline string
    val message = """
        Welcome to Kotlin!
        It's modern and concise.
    """.trimIndent()

    println(greeting)
    println(message)
}

String Templates

fun main() {
    val language = "Kotlin"
    val version = 1.9
    val year = 2024

    println("Language: $language")
    println("Version: $version")
    println("Born in: ${2011}")
    println("Current Year: $year")
    println("Age: ${year - 2011} years old")
}

String Length and Indexing

fun main() {
    val text = "Hello, Kotlin!"

    println(text.length)     // 14
    println(text[0])         // H
    println(text[7])         // K
    println(text.first())    // H
    println(text.last())     // !
}

Common String Functions

Case Operations

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

    println(str.uppercase())    // HELLO, WORLD!
    println(str.lowercase())    // hello, world!
    println(str.capitalize())   // Hello, world! (deprecated in newer Kotlin)
}

Trimming

fun main() {
    val padded = "   Hello, Kotlin!   "

    println(padded.trim())        // "Hello, Kotlin!"
    println(padded.trimStart())   // "Hello, Kotlin!   "
    println(padded.trimEnd())     // "   Hello, Kotlin!"
}

Substring

fun main() {
    val str = "Hello, Kotlin!"

    println(str.substring(7))          // Kotlin!
    println(str.substring(7, 13))      // Kotlin
    println(str.take(5))               // Hello
    println(str.drop(7))               // Kotlin!
    println(str.takeLast(7))           // Kotlin!
    println(str.dropLast(1))           // Hello, Kotlin
}

Checking Content

fun main() {
    val email = "user@example.com"

    println(email.contains("@"))          // true
    println(email.startsWith("user"))     // true
    println(email.endsWith(".com"))       // true
    println(email.isEmpty())             // false
    println(email.isNotEmpty())          // true
    println("   ".isBlank())             // true
}

Replacing

fun main() {
    val sentence = "I love Java. Java is great."

    println(sentence.replace("Java", "Kotlin"))
    // I love Kotlin. Kotlin is great.

    println(sentence.replaceFirst("Java", "Kotlin"))
    // I love Kotlin. Java is great.
}

Splitting

fun main() {
    val csv = "Alice,Bob,Charlie,Diana"
    val parts = csv.split(",")

    println(parts)           // [Alice, Bob, Charlie, Diana]
    println(parts.size)      // 4
    parts.forEach { println(it) }
}

Joining

fun main() {
    val words = listOf("Kotlin", "is", "awesome")
    val sentence = words.joinToString(" ")
    println(sentence)   // Kotlin is awesome

    val csv = words.joinToString(separator = ",", prefix = "[", postfix = "]")
    println(csv)        // [Kotlin,is,awesome]
}

String Comparison

fun main() {
    val s1 = "Kotlin"
    val s2 = "kotlin"

    println(s1 == s2)                         // false (case-sensitive)
    println(s1.equals(s2, ignoreCase = true)) // true
    println(s1.compareTo(s2))                 // negative (K < k in ASCII)
}

Converting Strings

fun main() {
    val numStr = "42"
    val decStr = "3.14"

    val num = numStr.toInt()
    val dec = decStr.toDouble()
    val safe = "abc".toIntOrNull()   // null (no crash)

    println(num)    // 42
    println(dec)    // 3.14
    println(safe)   // null
}

String Formatting

fun main() {
    val pi = 3.14159
    val formatted = "%.2f".format(pi)
    println(formatted)   // 3.14

    val name = "Alice"
    val age = 30
    val info = "%s is %d years old".format(name, age)
    println(info)   // Alice is 30 years old
}

Char Operations

fun main() {
    val ch = 'K'
    println(ch.isLetter())    // true
    println(ch.isDigit())     // false
    println(ch.isUpperCase()) // true
    println(ch.lowercaseChar())  // k
    println(ch.code)          // 75 (ASCII code)
}

Summary

Operation	Method
Length	str.length
Uppercase	str.uppercase()
Lowercase	str.lowercase()
Trim	str.trim()
Substring	str.substring(from, to)
Contains	str.contains("x")
Starts with	str.startsWith("x")
Replace	str.replace("old", "new")
Split	str.split(",")
Join	list.joinToString(separator)
Convert to Int	str.toInt() / toIntOrNull()