How to Remove Whitespace from String in Kotlin

In Kotlin, you can remove whitespace from a string using trim() to remove spaces at the start and end, or replace(" ", "") to remove all spaces inside the string. For more control, use filter with a condition to remove all whitespace characters.

Syntax

trim(): Removes whitespace only from the start and end of the string.

replace(oldValue, newValue): Replaces all occurrences of oldValue with newValue in the string.

filter { condition }: Keeps only characters that meet the condition, useful to remove all whitespace characters.

kotlin

val original = "  Hello World  "

val trimmed = original.trim()
val noSpaces = original.replace(" ", "")
val noWhitespace = original.filter { !it.isWhitespace() }

Example

This example shows how to remove whitespace from different parts of a string using trim(), replace(), and filter().

kotlin

fun main() {
    val text = "  Kotlin is fun!  "

    val trimmed = text.trim() // removes spaces at start and end
    val noSpaces = text.replace(" ", "") // removes all spaces
    val noWhitespace = text.filter { !it.isWhitespace() } // removes all whitespace characters

    println("Original: '$text'")
    println("Trimmed: '$trimmed'")
    println("No spaces: '$noSpaces'")
    println("No whitespace: '$noWhitespace'")
}

Output

Original: '  Kotlin is fun!  '
Trimmed: 'Kotlin is fun!'
No spaces: 'Kotlinisfun!'
No whitespace: 'Kotlinisfun!'

Common Pitfalls

Using trim() only removes spaces at the start and end, not inside the string. If you want to remove all spaces inside, you must use replace() or filter().

Replacing only space characters (' ') does not remove other whitespace like tabs or newlines. Use filter { !it.isWhitespace() } to remove all whitespace characters.

kotlin

fun main() {
    val text = "  Hello\tWorld \n "

    // Wrong: only removes spaces, tabs and newlines remain
    val replacedSpaces = text.replace(" ", "")

    // Right: removes all whitespace characters
    val removedWhitespace = text.filter { !it.isWhitespace() }

    println("Replaced spaces: '$replacedSpaces'")
    println("Removed all whitespace: '$removedWhitespace'")
}

Output

Replaced spaces: 'Hello\tWorld\n'
Removed all whitespace: 'HelloWorld'

Quick Reference

Function	Description	Example
trim()	Removes whitespace from start and end	" text ".trim() -> "text"
replace(" ", "")	Removes all space characters inside string	"a b c".replace(" ", "") -> "abc"
filter { !it.isWhitespace() }	Removes all whitespace characters (spaces, tabs, newlines)	"a\tb\nc".filter { !it.isWhitespace() } -> "abc"

Key Takeaways

Use trim() to remove spaces only at the start and end of a string.

Use replace(" ", "") to remove all space characters inside the string.

Use filter { !it.isWhitespace() } to remove all types of whitespace characters.

Replacing spaces does not remove tabs or newlines; use filter for full whitespace removal.

Choose the method based on whether you want to remove whitespace only at edges or everywhere.