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Kotlin Regex

Regex is generally refers to regular expression which is used to search string or replace on regex object. To use it functionality we need to use Regex(pattern: String) class. Kotlin'sRegex class is found in kotlin.text.regex package.

Kotlin Regex Constructor

Regex(pattern: String) It creates a regular expression from the given string pattern.
Regex(pattern: String, option: RegexOption) It creates a regular expression from the given string pattern and given single option.
Regex(pattern: String, options: Set<RegexOption>) It creates a regular expression from the given string pattern and set of given options.

Regex Functions

Functions Descriptions
fun containsMatchIn(input: CharSequence): Boolean It indicates that regular expression contains at least one input character
fun find(
input: CharSequence,
startIndex: Int = 0
): MatchResult?
It returns the first match of regular expression in the input character sequence, begins from given startIndex.
fun findAll(
input: CharSequence,
startIndex: Int = 0
): Sequence<MatchResult>
It returns all occurrences of regular expression in the input string, starts from the given startIndex.
funmatchEntire(input: CharSequence): MatchResult? It is used to match complete input character from the pattern.
infix fun matches(input: CharSequence): Boolean It indicates whether all input character sequence matches in regular expression.
fun replace(input: CharSequence, replacement: String): String It replaces all the input character sequence of regular expression with given replacement string.
fun replaceFirst(
input: CharSequence,
replacement: String
): String
It replaces the first occurrence of regular expression in the given input string with given replacement string.
fun split(input: CharSequence, limit: Int = 0): List<String> It splits the input character sequence of regular expression.
fun toPattern(): Pattern
fun toString(): String
It returns the regular expression in string.

Example of Regex class checking contains of input pattern

Output:

true

The result of Regex function is based on matching regex pattern and the input string. Some function checks partial match while some checks full match.

Regex example of containsMatchIn()

Output:

true

Regex example of matches(input: CharSequence): Boolean

The matches(input: CharSequence): Booleanfunction of regex checksall input character sequence matches in regular expression.

Output:

false
false
true

Regex example of matchEntire(input: CharSequence): MatchResult?

The matchEntire() function is used to match complete input character from the pattern.

Output:

abcd
null
100
null

Regex example offind(input: CharSequence, startIndex: Int = 0): MatchResult?

The find function is used to find the input character sequence from regex object.

Output:

mymail@google.com
123-456-7890

Regex example offindAll(input: CharSequence, startIndex: Int = 0): Sequence<MatchResult>

The findAll() function of regex returns sequence of match result on the basis of pattern provided.

Output:

12 34 56 7 8

Regex example ofreplace(input: CharSequence, replacement: String): String

Regex replace() function replaces the all the matching pattern from input character sequence with specified replacement string.

Output:

this picture is awesome

Regex example ofreplaceFirst(input: CharSequence, replacement: String): String

Regex replaceFirst() function replaces the first occurrence of matching pattern from input character sequence with specified replacement string.

Output:

nature is awesome, beautiful is nature

Regex example ofsplit(input: CharSequence, limit: Int = 0): List<String>

The regex split() function splits input character sequence according to pattern provided. This splits value are returned in List.

Output:

[ab, cd, ef]
[nothing match to split]





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