Kotlin program to remove special characters from a string

Introduction :

In this tutorial, we will learn how to remove all special characters from a string in Kotlin. Our program will remove all non-alphanumeric characters excluding space. For example, if the string is abc 123 *&^, it will print abc 123.

I will show two different ways to solve it in Kotlin. Just try to run the sample programs with different strings.

Method 1: Using regex :

regex or regular expression is a sequence of characters used to match characters in a string. We can use the below regular expression :

[^A-Za-z0-9 ]

It will match all characters that are not in between A to Z and not in between a to z and not in between 0 to 9 and not a blank space. Then we will simply replace those characters with an empty character.

fun main() {
    var str = "Hello !!!๐Ÿ˜Žworld @1233*@@():)๐Ÿ‘Œ๐Ÿ‘Œ๐Ÿ‘Œ"

    val re = "[^A-Za-z0-9 ]".toRegex()
    str = re.replace(str, "")


It will print the below output :

Hello world 1233

toRegex() method is used to convert one string to a regular expression. replace method is used to replace all characters matched by that regex with empty space.

Kotlin remove special characters from string regex

Method 2: Using filter :

filter is another way to remove unwanted characters from a string. It takes one predicate and returns a string containing only those characters from the original string that matches the predicate. Below is the complete program :

fun main() {
    var str = "Hello !!!๐Ÿ˜Žworld @1233*@@():)๐Ÿ‘Œ๐Ÿ‘Œ๐Ÿ‘Œ"

    str = str.filter{ it.isLetterOrDigit() || it.isWhitespace() }


We are checking if the character is a letter or digit or whitespace or not. The final result is the same as the above example.

Kotlin remove special characters from string filter