Regex in Kotlin Android Studio

In this article, we will learn about Regex in Kotlin. Regex is used to refer to a regular expression that is used to search a string or replace a pattern in a String. To use it, we need Regex(pattern: String) class and Kotlin.regex.text package.

Constructor

Regex(pattern: String)	It will give string pattern.
Regex(pattern: String, option: RegexOption)	It will give string pattern and single option.
Regex(pattern: String, options: Set<RegexOption>)	It will give a string pattern and a set of giving options.

Properties

Following are the properties of Regex Kotlin

val options: Set<RegexOption>	It contains the set of options that are to be used at the time of regex creation.
val pattern: String	It contains the string describing the pattern.

Regex Functions

Some of the following functions are as fellows

containsMatchIn()

This function returns a Boolean indicating whether there exists any match of our pattern in the input.

fun containsMatchIn(input: CharSequence): Boolean

Example to demonstrate containsMatchIn() function in Kotlin

fun main() 
{ 
	// Regex to match any string starting with 'a' 
	val pattern = Regex("^a") 
	println(pattern.containsMatchIn("abc")) 
	println(pattern.containsMatchIn("bac")) 
}

Output

true
false

find()

This function returns the first matched substring pertaining to our pattern in the input, from the specified starting index.

fun find(input: CharSequence, startIndex: Int): MatchResult?

Example to demonstrate find() function in Kotlin

fun main() 
{ 
	// Regex to match "ll" in a string 
	val pattern1 = Regex("ll") 
	val ans : MatchResult? = pattern1.find("HelloWorld", 1) 
	println(ans?.value) 
}