Dart string
last modified October 18, 2026
Dart string tutorial shows how to work with strings in Dart language.
Dart string
A string is a sequence of UTF-16 code units. It is used to represent some text in a program. A character may be represented by multiple code points. Each code point can have one or two code units.
Strings are immutable in Dart. There are methods such as
toLowerCase or split that return a modified string,
but the original string is intact.
A rune is an integer representing a Unicode code point. The
runes property of a string returns its runes.
A string in Dart is an object of the String class. There are
several methods that we can call on a string object.
Dart simple string
The following is a simple Dart program with strings.
void main() {
final text = 'There are six falcons';
print(text);
final len = text.length;
print('The string has ' + len.toString() + ' characters');
final word = 'falcon ';
print(word * 3);
}
String literals are delimited with single or double quotes.
final len = text.length;
The length property returns the length of the string, i.e. the
number of UTF-16 code units in the string.
print('The string has ' + len.toString() + ' characters');
Strings can be concatenated with the + operator. The number must
be converted to a string first; the interpolation shown later is usually
nicer.
final word = 'falcon '; print(word * 3);
The * operator repeats a string.
$ dart main.dart There are six falcons The string has 21 characters falcon falcon falcon
Dart string delimiters
Strings are delimited either with single or double quotes. The quotes can be nested to create quotations or direct speech if needed. Otherwise, the inner quote must be escaped with a backslash.
void main() {
final text1 = "old falcon";
final text2 = 'new book';
final text3 = "This was a 'great movie'";
final text4 = 'He said: "I saw an old man in the park."';
final text5 = 'It\'s a nice day';
print(text1);
print(text2);
print(text3);
print(text4);
print(text5);
}
The example presents string delimiters in Dart. Adjacent string literals are
joined by the compiler, which is handy for splitting a long text into several
lines of source code:
'one ' 'two ' 'three' is the same as 'one two three'.
$ dart main.dart old falcon new book This was a 'great movie' He said: "I saw an old man in the park." It's a nice day
Dart string length
The length property returns the length of a string in UTF-16 code
units.
void main() {
final word = 'čerešňa';
print(word.length);
print(word.codeUnits);
print(word.runes);
final word2 = '合気道';
print(word2.length);
print(word2.codeUnits);
print(word2.runes);
final emoji = '🐘';
print(emoji.length);
print(emoji.runes.length);
}
In the example, we have strings with non-ASCII characters. The
codeUnits property returns an unmodifiable list of the UTF-16 code
units of the string. The runes property returns an iterable of
Unicode code points. For most characters, there is one code unit per code point.
Characters outside the Basic Multilingual Plane, such as the elephant emoji,
take two code units, so length returns 2 for a single visible
symbol.
$ dart main.dart 7 [269, 101, 114, 101, 353, 328, 97] (269, 101, 114, 101, 353, 328, 97) 3 [21512, 27671, 36947] (21512, 27671, 36947) 2 1
Dart multiline string
Multiline strings are created with triple single or double quotes.
void main() {
final sonnet55 = '''
Not marble nor the gilded monuments
Of princes shall outlive this powerful rhyme,
But you shall shine more bright in these contents
Than unswept stone besmeared with sluttish time.
When wasteful war shall statues overturn,
And broils root out the work of masonry,
Nor Mars his sword nor war's quick fire shall burn
The living record of your memory.
'Gainst death and all-oblivious enmity
Shall you pace forth; your praise shall still find room
Even in the eyes of all posterity
That wear this world out to the ending doom.
So, till the Judgement that yourself arise,
You live in this, and dwell in lovers' eyes.''';
print(sonnet55);
}
The example prints a verse created with triple single quotes. A newline directly after the opening quotes is ignored, which lets us start the text on its own line.
$ dart main.dart Not marble nor the gilded monuments Of princes shall outlive this powerful rhyme, But you shall shine more bright in these contents Than unswept stone besmeared with sluttish time. When wasteful war shall statues overturn, And broils root out the work of masonry, Nor Mars his sword nor war's quick fire shall burn The living record of your memory. 'Gainst death and all-oblivious enmity Shall you pace forth; your praise shall still find room Even in the eyes of all posterity That wear this world out to the ending doom. So, till the Judgement that yourself arise, You live in this, and dwell in lovers' eyes.
Dart string is immutable
A string cannot be modified. We can call methods that return a modified string.
void main() {
final text = 'a red fox';
final parts = text.split(' ');
print(parts);
print(text);
print(text.toUpperCase());
print(text);
}
With the split method, we split the string at matches of the pattern
and return a list of substrings. The toUpperCase method returns a
new string. The original string is preserved.
$ dart main.dart [a, red, fox] a red fox A RED FOX a red fox
Dart string escape sequences
Escape sequences are special characters that have a specific meaning when used
within a string literal. For instance, the new-line \n escape
sequence causes the next character to appear on a new line.
void main() {
final text1 = 'a red \n fox';
final text2 = 'a red \t fox';
final text3 = 'a red \u0041 \u{1F98A} fox';
final text4 = 'a red \x41 fox';
print(text1);
print(text2);
print(text3);
print(text4);
}
In the example, we use several escape sequences. The \n adds a
newline, the \t inserts a tab. The \u0041 and
\x41 forms insert a character by its code (here the letter A), and
\u{1F98A} is the form for code points with more than four hex
digits (a fox emoji). Other escapes are \\ for a backslash,
\$ for a dollar sign, \r for a carriage return, and
\b for the backspace control character, which most terminals
interpret as a cursor move.
$ dart main.dart a red fox a red fox a red A 🦊 fox a red A fox
Dart raw string
In raw strings, the escape characters are not interpreted. A raw string is
created by prepending a string literal with the r character. Raw
strings are useful for regular expressions and Windows paths.
void main() {
print(r'falcon\tfalcon\tfalcon');
print('becomes');
print('falcon\tfalcon\tfalcon');
}
The example uses a raw string.
$ dart main.dart falcon\tfalcon\tfalcon becomes falcon falcon falcon
Dart string interpolation
String interpolation is the process of evaluating a string containing variables and expressions. When an interpolated string is evaluated the variables and expressions are replaced with their corresponding values.
In Dart, the $ is used to interpolate variables and
${} expressions.
void main() {
final name = 'John Doe';
final occupation = 'gardener';
print('$name is a $occupation');
final x = 12;
final y = 14;
print('$x * $y = ${x * y}');
final words = ['falcon', 'owl'];
print('Count: ${words.length}, first: ${words.first.toUpperCase()}');
}
In the example, we interpolate variables and expressions.
print('$name is a $occupation');
Variables are interpolated by prepending their names with the dollar sign.
print('$x * $y = ${x * y}');
If we need to evaluate more complex expressions, such as an arithmetic
operation or a property access, we use ${}. The braces can be
omitted only for simple identifiers.
$ dart main.dart John Doe is a gardener 12 * 14 = 168 Count: 2, first: FALCON
If we need to output a dollar sign, we escape it: \$.
void main() {
final item = 'beer';
final price = 4.5;
print('The price of a $item is \$$price');
}
The example prints the price of a beer in dollars.
$ dart main.dart The price of a beer is $4.5
Dart string isEmpty/isNotEmpty
With isEmpty and isNotEmpty we can check if a string
in Dart is empty or not empty, respectively.
void main() {
final word1 = '';
final word2 = 'falcon';
if (word1.isEmpty) {
print('word1 is empty');
} else {
print('word1 is not empty');
}
if (word2.isNotEmpty) {
print('word2 is not empty');
} else {
print('word2 is empty');
}
}
The example calls the properties on two words. They are preferable to comparing the length with zero.
$ dart main.dart word1 is empty word2 is not empty
Dart trim string
We can remove whitespace from the string with trim,
trimLeft, and trimRight methods.
void main() {
final word = ' falcon\t';
print('|$word|');
print('|${word.trim()}|');
print('|${word.trimLeft()}|');
print('|${word.trimRight()}|');
print('|$word|');
}
The example uses the methods on a string which has leading and trailing whitespace characters. The tab at the end of the original string is rendered as spaces by the terminal.
$ dart main.dart | falcon | |falcon| |falcon | | falcon| | falcon |
Dart string search
The contains, startsWith, endsWith,
indexOf, and lastIndexOf methods search in a string.
The index methods return -1 when there is no match.
void main() {
const text = 'The old falcon watches the old river';
print(text.contains('falcon'));
print(text.startsWith('The'));
print(text.endsWith('river'));
print(text.indexOf('old'));
print(text.lastIndexOf('old'));
print(text.indexOf('old', 5));
print(text.indexOf('snow'));
}
The optional second argument of indexOf is the position where the
search starts; thus, the third call finds the second occurrence of "old".
$ dart main.dart true true true 4 27 27 -1
Dart substring and replace
The substring method returns a part of a string. The
replaceAll and replaceFirst methods replace
occurrences of a pattern with another string.
void main() {
const text = 'The old falcon';
print(text.substring(4));
print(text.substring(4, 7));
print(text.replaceAll('old', 'young'));
print(text.replaceFirst('o', '0'));
print(text.replaceAll(RegExp(r'[aeiou]'), '*'));
}
The end index of substring is exclusive. Invalid indexes throw a
RangeError. The patterns can be regular expressions.
$ dart main.dart old falcon old The young falcon The 0ld falcon Th* *ld f*lc*n
Dart string case and padding
The toUpperCase and toLowerCase methods change the
case. The padLeft and padRight methods pad a string to
a minimum width, which is useful for aligning columns.
void main() {
const name = 'falcon';
print(name.toUpperCase());
print('FALCON'.toLowerCase());
print('|${name.padLeft(10)}|');
print('|${name.padRight(10, '.')}|');
print('7'.padLeft(3, '0'));
final items = {'apple': 3, 'banana': 12, 'kiwi': 7};
items.forEach((k, v) => print('${k.padRight(8)}${v.toString().padLeft(3)}'));
}
Without the second argument, the padding character is a space.
$ dart main.dart FALCON falcon | falcon| |falcon....| 007 apple 3 banana 12 kiwi 7
Dart string comparison
Strings are compared for equality with the == operator, which
compares the content. The compareTo method returns a negative
number, zero, or a positive number and is used for ordering. The comparison is
based on UTF-16 code units, so it is case-sensitive.
void main() {
print('falcon' == 'falcon');
print('falcon' == 'Falcon');
print('falcon'.toLowerCase() == 'Falcon'.toLowerCase());
print('apple'.compareTo('banana'));
print('banana'.compareTo('apple'));
print('apple'.compareTo('apple'));
print('Zebra'.compareTo('apple'));
}
The upper-case letter Z has a smaller code than the lower-case a; therefore, "Zebra" is ordered before "apple".
$ dart main.dart true false true -1 1 0 -1
Dart string join
The join method of an iterable concatenates its elements with a
separator.
void main() {
final words = ['sky', 'cloud', 'rain'];
print(words.join());
print(words.join(', '));
print(words.map((w) => w.toUpperCase()).join('-'));
}
Without an argument, join uses an empty separator.
$ dart main.dart skycloudrain sky, cloud, rain SKY-CLOUD-RAIN
Dart string iterate
We can iterate over the elements of a string with the help of the
runes property and the String.fromCharCode method.
Indexing a string with [] returns a code unit as a one-character
string.
void main() {
const word = 'falcon';
for (final c in word.runes) {
print(String.fromCharCode(c));
}
print(word[0]);
print(word.codeUnitAt(0));
print(word.split('').reversed.join());
}
The example prints the characters of the 'falcon' word to the terminal; each on
a separate line. Then it shows the first character, its code, and the reversed
word. Note that reversing with split('') breaks characters outside
the Basic Multilingual Plane; the characters package handles such
cases.
$ dart main.dart f a l c o n f 102 noclaf
Dart nullable strings
With null safety, a String cannot be null. A variable that may have
no value is declared as String?. The null-aware operators make
working with such values concise.
void main() {
String? name;
print(name?.length);
print(name ?? 'anonymous');
name = 'Jane';
print(name.length);
print(name?.toUpperCase());
}
The ?. operator short-circuits to null and ?? provides
a default. After the assignment, the compiler knows that name is not
null, so length can be accessed directly (type promotion).
$ dart main.dart null anonymous 4 JANE
Source
In this article we have covered strings in Dart.
Author
List all Dart tutorials.