Remove leading and trailing whitespace from a string in Kotlin

This post will discuss how to remove leading and trailing whitespace from a string in Kotlin.

1. Using `trim()` function

The standard solution to trim a string is using the trim() function. Since the string is immutable in Kotlin, it returns a new string having leading and trailing whitespace removed. To just remove the leading whitespaces, use the trimStart() function. Similarly, use the trimEnd() function to remove the trailing whitespaces.

fun main() {

val s = " [Some Text] "

println(s.trim()) // [Some Text]

}

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Here’s an equivalent version using a predicate it <= ' ', which removes all the non-printable ASCII characters from the string (having ASCII code less or equal to the space).

fun main() {

val s = " [Some Text] "

println(s.trim { it <= ' ' }) // [Some Text]

}

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2. Using `replace()` function

The replace() function is overloaded to accept a regular expression and replace each substring of the char sequence that matches the given regular expression with the given replacement. It can be used as follows to trim a string:

fun trim(s: String): String {

return s.replace("^\\s+|\\s+$".toRegex(), "")

}

fun main() {

val s = " [Some Text] "

println(trim(s)) // [Some Text]

}

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To remove either the leading whitespaces or the trailing whitespaces from the string, use the following utility functions:

fun ltrim(str: String): String {

return str.replace("^\\s+".toRegex(), "")

}

fun rtrim(str: String): String {

return str.replace("\\s+$".toRegex(), "")

}

3. Custom Routine

You can even write a custom routine for trimming a string, which doesn't involve using any regex and runs comparatively faster. Below is a simple custom implementation of the trim() function.

fun trim(s: String): String {

var i = 0

while (i < s.length && s[i].isWhitespace()) {

i++

}

var j = s.length - 1

while (j >= 0 && s[j].isWhitespace()) {

j--

}

return s.substring(i, j + 1)

}

fun main() {

val s = " [Some Text] "

println(trim(s)) // [Some Text]

}

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The following utility function can be used to remove the leading or the trailing whitespaces from a string.

fun ltrim(str: String): String {

var i = 0

while (i < str.length && str[i].isWhitespace()) {

i++

}

return str.substring(i)

}

fun rtrim(str: String): String {

var i = str.length - 1

while (i >= 0 && str[i].isWhitespace()) {

i--

}

return str.substring(0, i + 1)

}

That's all about removing leading and trailing whitespace from a string in Kotlin.

Remove leading and trailing whitespace from a string in Kotlin

1. Using trim() function

2. Using replace() function

3. Custom Routine

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1. Using `trim()` function

2. Using `replace()` function