A sequence of UTF-16 code units.

Strings are mainly used to represent text. A character may be represented bymultiple code points, each code point consisting of one or two codeunits. For example, the Papua New Guinea flag character requires four codeunits to represent two code points, but should be treated like a singlecharacter: "🇵🇬". Platforms that do not support the flag character may showthe letters "PG" instead. If the code points are swapped, it instead becomesthe Guadeloupe flag "🇬🇵" ("GP").

A string can be either single or multiline. Single line strings arewritten using matching single or double quotes, and multiline strings arewritten using triple quotes. The following are all valid Dart strings:

'Single quotes';"Double quotes";'Double quotes in "single" quotes';"Single quotes in 'double' quotes";'''Amultilinestring''';"""Anothermultilinestring""";

Strings are immutable. Although you cannot change a string, you can performan operation on a string which creates a new string:

const string = 'Dart is fun';print(string.substring(0, 4)); // 'Dart'

You can use the plus (+) operator to concatenate strings:

const string = 'Dart ' + 'is ' + 'fun!';print(string); // 'Dart is fun!'

Adjacent string literals are concatenated automatically:

const string = 'Dart ' 'is ' 'fun!';print(string); // 'Dart is fun!'

You can use${} to interpolate the value of Dart expressionswithin strings. The curly braces can be omitted when evaluating identifiers:

const string = 'dartlang';print('$string has ${string.length} letters'); // dartlang has 8 letters

A string is represented by a sequence of Unicode UTF-16 code unitsaccessible through thecodeUnitAt or thecodeUnits members:

const string = 'Dart';final firstCodeUnit = string.codeUnitAt(0);print(firstCodeUnit); // 68, aka U+0044, the code point for 'D'.final allCodeUnits = string.codeUnits;print(allCodeUnits); // [68, 97, 114, 116]

A string representation of the individual code units is accessible throughthe index operator:

const string = 'Dart';final charAtIndex = string[0];print(charAtIndex); // 'D'

The characters of a string are encoded in UTF-16. Decoding UTF-16, whichcombines surrogate pairs, yields Unicode code points. Following a similarterminology to Go, Dart uses the name 'rune' for an integer representing aUnicode code point. Use therunes property to get the runes of a string:

const string = 'Dart';final runes = string.runes.toList();print(runes); // [68, 97, 114, 116]

For a character outside the Basic Multilingual Plane (plane 0) that iscomposed of a surrogate pair,runes combines the pair and returns asingle integer. For example, the Unicode character for amusical G-clef ('𝄞') with rune value 0x1D11E consists of a UTF-16 surrogatepair:0xD834 and0xDD1E. UsingcodeUnits returns the surrogate pair,and usingrunes returns their combined value:

const clef = '\u{1D11E}';for (final item in clef.codeUnits) {  print(item.toRadixString(16));  // d834  // dd1e}for (final item in clef.runes) {  print(item.toRadixString(16)); // 1d11e}

TheString class cannot be extended or implemented. Attempting to do soyields a compile-time error.

Other resources

• StringBuffer to efficiently build a string incrementally.
• RegExp to work with regular expressions.
• Strings and regular expressions

Implemented types

• Comparable<String>
• Pattern

Available extensions

• StringToJSString

Constructors

String.fromCharCode(intcharCode)

Allocates a new string containing the specifiedcharCode.

factory

String.fromCharCodes(Iterable<int>charCodes, [intstart =0,int?end])

Allocates a new string containing the specifiedcharCodes.

factory

String.fromEnvironment(Stringname, {StringdefaultValue =""})

Value forname in the compilation configuration environment declaration.

const

factory

Properties

codeUnits→List<int>

An unmodifiable list of the UTF-16 code units of this string.

no setter

hashCode→int

A hash code derived from the code units of the string.

no setteroverride

isEmpty→bool

Whether this string is empty.

no setter

isNotEmpty→bool

Whether this string is not empty.

no setter

length→int

The length of the string.

no setter

runes→Runes

AnIterable of Unicode code-points of this string.

no setter

runtimeType→Type

A representation of the runtime type of the object.

no setterinherited

toJS→JSString

Available onString, provided by theStringToJSString extension

Converts thisString to aJSString.

no setter

Methods

allMatches(Stringstring, [intstart =0])→Iterable<Match>

Matches this pattern against the string repeatedly.

inherited

codeUnitAt(intindex)→int

Returns the 16-bit UTF-16 code unit at the givenindex.

compareTo(Stringother)→int

Compares this string toother.

override

contains(Patternother, [intstartIndex =0])→bool

Whether this string contains a match ofother.

endsWith(Stringother)→bool

Whether this string ends withother.

indexOf(Patternpattern, [intstart =0])→int

Returns the position of the first match ofpattern in this string,starting atstart, inclusive:

lastIndexOf(Patternpattern, [int?start])→int

The starting position of the last matchpattern in this string.

matchAsPrefix(Stringstring, [intstart =0])→Match?

Matches this pattern against the start ofstring.

inherited

noSuchMethod(Invocationinvocation)→ dynamic

Invoked when a nonexistent method or property is accessed.

inherited

padLeft(intwidth, [Stringpadding =' '])→String

Pads this string on the left if it is shorter thanwidth.

padRight(intwidth, [Stringpadding =' '])→String

Pads this string on the right if it is shorter thanwidth.

replaceAll(Patternfrom,Stringreplace)→String

Replaces all substrings that matchfrom withreplace.

replaceAllMapped(Patternfrom,Stringreplace(Matchmatch))→String

Replace all substrings that matchfrom by a computed string.

replaceFirst(Patternfrom,Stringto, [intstartIndex =0])→String

Creates a new string with the first occurrence offrom replaced byto.

replaceFirstMapped(Patternfrom,Stringreplace(Matchmatch), [intstartIndex =0])→String

Replace the first occurrence offrom in this string.

replaceRange(intstart,int?end,Stringreplacement)→String

Replaces the substring fromstart toend withreplacement.

split(Patternpattern)→List<String>

Splits the string at matches ofpattern and returns a list of substrings.

splitMapJoin(Patternpattern, {StringonMatch(Match)?,StringonNonMatch(String)?})→String

Splits the string, converts its parts, and combines them into a newstring.

startsWith(Patternpattern, [intindex =0])→bool

Whether this string starts with a match ofpattern.

substring(intstart, [int?end])→String

The substring of this string fromstart, inclusive, toend, exclusive.

toLowerCase()→String

Converts all characters in this string to lower case.

toString()→String

A string representation of this object.

inherited

toUpperCase()→String

Converts all characters in this string to upper case.

trim()→String

The string without any leading and trailing whitespace.

trimLeft()→String

The string without any leading whitespace.

trimRight()→String

The string without any trailing whitespace.

Operators

operator *(inttimes)→String

Creates a new string by concatenating this string with itself a numberof times.

operator +(Stringother)→String

Creates a new string by concatenating this string withother.

operator ==(Objectother)→bool

Whetherother is aString with the same sequence of code units.

override

operator [](intindex)→String

The character (as a single-code-unitString) at the givenindex.