Kotlin Regular Expression

Rugular Expressions are a basic part of almost every programming language. These are utilized for text searching and advanced content developement.

12. Kotlin Regular Expression 12.1 Regex() Class 12.2 Pattern Regular Expression 12.3 Regex() functions

Kotlin Regex() Class

The regular expression is used to find or search text in a content. To deal with regular expression, Kotlin provides Regex() class, that has many functions to deal with regular expressions. An object of this class represents a regular expression, that can be used for string searching purposes.

Syntax of Regex()

Regex(pattern: String, option: RegexOption)

In the above syntax, string is the input type and pattern is the regular expression that defines the text we are looking for. The option parameter is optional that contains a single option.

Example of Regex()

var r = Regex(pattern: x)

Pattern Regular Expression

A pattern is a regular expression that characterizes the content we are looking for or controlling. It comprises of text literals and metacharacters. Metacharacters are special characters that control how the regular expression will be assessed.

Regex	Matching
.	to match any single string
+	to match the preceding element once or more times
*	to match the preceding element zero or more times
^	to match the starting position of a string
$	to match the ending position of a string
?	to match preceding element only once.
|	or operator
[abc]	to match within a, or b, or c
[^abc]	to match except a, or b, or c
[a-c]	to match in range a to c
\s	to match white space character
\w	to match a word character

Kotlin Regex() functions

Kotlin find() method

It returns the first match substring of a regular expression, beginning at the specified start index. The start index is 0 by default.

fun main(args : Array<String>)  { 
	val regex = """(abcd|efgh)""".toRegex()
    val match = regex.find("abc fg")
}

Kotlin findAll() method

It returns all possible matching substrings of a regular expression, beginning at the specified start index.

fun main(args : Array<String>)  { 
	val regex = """(abcd|efgh)""".toRegex()
	val match = regex.findAll("abc")
}

Kotlin matchEntire() method

It is used to match the entire character of a regular expression.

fun main(args : Array<String>)  { 
	val regex = """(abcd|efgh)""".toRegex()  
	val match = regex.matchEntire("abcd")?.value  
}

Kotlin matches() method

It is a boolean function that checks all the matched input character sequence in a regular expression.

fun main(args : Array<String>)  { 
	val regex = """(abcd|efgh)""".toRegex()  
	val match = regex.matches("abcd")?.value  
}

Kotlin replace() method

It replaces all occurrences of the regular expression in the specified input string.

fun main(args : Array<String>)  { 
	val regex = """(east|west)""".toRegex()
	val zone = "Table is in east zone, chair is in west zone."  
	val newzone = regex.replace(zone, "center")
	println(newzone)
}

Output

Table is in center zone, chair is in center zone.

Kotlin replaceFirst() method

It replaces only the first occurrence of the regular expression in the specified input string.

fun main(args : Array<String>)  { 
	val regex = """(east|west)""".toRegex()
	val zone = "Table is in east zone, chair is in west zone."  
	val newzone = regex.replaceFirst(zone, "center")
	println(newzone)
}

Output

Table is in center zone, chair is in west zone.