Common String Functions

Searching and Checking

Example

These functions answer questions about a string.

fun main() {
    val email = "[email protected]"
    println(email.contains("@"))
    println(email.startsWith("asha"))
    println(email.endsWith(".com"))
    println(email.indexOf('@'))
    println(email.substringBefore("@"))
    println(email.substringAfter("@"))
    println("   ".isBlank())
    println("".isEmpty())
}

Output

true
true
true
8
asha.rao
gmail.com
true
true

Transforming

Example

These functions return a new, changed string.

fun main() {
    val raw = "  Hello Kotlin World  "
    println("[${raw.trim()}]")
    println(raw.trim().lowercase())
    println(raw.trim().replace("World", "Android"))
    println(raw.trim().substring(6, 12))
    println("ab".repeat(3))
    println("Kotlin".reversed())
    println("7".padStart(3, '0'))
    println("chicken biryani".replaceFirstChar { it.uppercase() })
}

Output

[Hello Kotlin World]
hello kotlin world
Hello Kotlin Android
Kotlin
ababab
niltoK
007
Chicken biryani

Splitting and Looping

Example

split turns a string into a list. You can also loop over the characters.

fun main() {
    val tags = "veg,spicy,bestseller"
    val list = tags.split(",")
    println(list)
    println(list.size)

    for (ch in "UPI") {
        print("$ch-")
    }
    println()
    println("a1b2c3".count { it.isDigit() })
}

Output

[veg, spicy, bestseller]
3
U-P-I-
3

Cheat Sheet

Function	Result for `"Kotlin"`
`length`	6
`uppercase()` / `lowercase()`	KOTLIN / kotlin
`substring(0, 3)`	Kot
`contains("tl")`	true
`indexOf('l')`	3
`replace("K", "C")`	Cotlin
`reversed()`	niltoK
`take(3)` / `drop(3)`	Kot / lin
`padEnd(8, '*')`	Kotlin**