Dart Beginner Lesson 11 of 107 4 min read

Dart String Methods: Complete List with Easy Examples

Every common Dart string method with a short, runnable example: trim, toUpperCase, contains, substring, split, replaceAll, padLeft, parse and more.

The Strings lesson showed how to create text and use interpolation. This page is a reference you can come back to: the string methods you will use most, grouped by job, each with a tiny program you can run and change.

Remember one rule while you read: strings never change. Every method below returns a new string (or a value) and leaves the original alone.

Quick reference table

Changing case and removing spaces

void main() {
  var name = '  Dart Tutorial  ';

  print('[${name.trim()}]');
  print('[${name.trimLeft()}]');
  print('[${name.trimRight()}]');
  print(name.trim().toUpperCase());
  print(name.trim().toLowerCase());
}

[Dart Tutorial]
[Dart Tutorial  ]
[  Dart Tutorial]
DART TUTORIAL
dart tutorial

The square brackets are only there so you can see where the spaces are. trim() is the first thing to call on anything a user types.

Searching inside a string

void main() {
  var text = 'Learn Dart, then learn Flutter';

  print(text.contains('Dart'));
  print(text.contains('dart'));     // case matters
  print(text.startsWith('Learn'));
  print(text.endsWith('Flutter'));
  print(text.indexOf('learn'));
  print(text.indexOf('Flutter'));
  print(text.indexOf('Java'));      // -1 means not found
}

true
false
true
true
17
23
-1

To search without caring about capitals, change both sides to the same case first: text.toLowerCase().contains('dart').

Getting part of a string

Positions start at 0. substring(start, end) includes start and stops before end.

void main() {
  var word = 'Flutter';

  print(word.length);
  print(word[0]);                  // first character
  print(word[word.length - 1]);    // last character
  print(word.substring(0, 4));
  print(word.substring(4));        // from 4 to the end
}

7
F
r
Flut
ter

Splitting, joining and replacing

void main() {
  var csv = 'apple,banana,mango';

  var fruits = csv.split(',');
  print(fruits);
  print(fruits.length);
  print(fruits.join(' | '));

  print(csv.replaceAll(',', ' and '));
  print(csv.replaceFirst('apple', 'grape'));

  var messy = 'Dart   is    fun';
  print(messy.replaceAll(RegExp(r'\s+'), ' '));
}

[apple, banana, mango]
3
apple | banana | mango
apple and banana and mango
grape,banana,mango
Dart is fun

split turns a string into a List; join turns a list back into a string. The last line uses a regular expression to squeeze many spaces into one.

Padding and repeating

void main() {
  print('5'.padLeft(3, '0'));
  print('Hi'.padRight(6, '.') + '|');
  print('-' * 20);
  print('ab' * 3);

  for (var i = 1; i <= 3; i++) {
    print('Item ${i.toString().padLeft(2)}: ok');
  }
}

005
Hi....|
--------------------
ababab
Item  1: ok
Item  2: ok
Item  3: ok

Padding is handy for invoice numbers (007) and for lining up columns in console output.

Checking and comparing

void main() {
  print(''.isEmpty);
  print('   '.isEmpty);          // spaces are characters
  print('   '.trim().isEmpty);
  print('Dart'.isNotEmpty);

  print('Dart' == 'Dart');
  print('Dart' == 'dart');
  print('Dart'.toLowerCase() == 'dart');
  print('apple'.compareTo('banana')); // negative: apple comes first
}

true
false
true
true
true
false
true
-1

Converting strings to numbers and back

void main() {
  print(int.parse('42') + 8);
  print(double.parse('3.5') * 2);
  print(int.tryParse('abc'));        // null instead of a crash
  print(int.tryParse('abc') ?? 0);   // fall back to 0

  print(42.toString() + '!');
  print(3.14159.toStringAsFixed(2));
}

50
7.0
null
0
42!
3.14

Use int.parse when you are sure the text is a number, and int.tryParse when it comes from a user. More in Type conversion.

Three small string programs

Capitalise every word:

void main() {
  var title = 'learn dart and flutter';

  var result = title
      .split(' ')
      .map((w) => w[0].toUpperCase() + w.substring(1))
      .join(' ');

  print(result);
}

Learn Dart And Flutter

Count the vowels:

void main() {
  var text = 'Dart Tutorial';

  var vowels = text
      .toLowerCase()
      .split('')
      .where((c) => 'aeiou'.contains(c))
      .length;

  print('Vowels in "$text": $vowels');
}

Vowels in "Dart Tutorial": 5

Check for a palindrome:

bool isPalindrome(String s) {
  var clean = s.toLowerCase();
  return clean == clean.split('').reversed.join();
}

void main() {
  for (var word in ['Level', 'Dart', 'Racecar']) {
    print('$word: ${isPalindrome(word)}');
  }
}

Level: true
Dart: false
Racecar: true

Common mistakes

• Expecting the original to change. name.trim(); on its own does nothing useful. Write name = name.trim();.
• Index out of range. 'Dart'[4] and 'Dart'.substring(2, 9) throw a RangeError. Check length first.
• Using parse on user input. int.parse('12a') throws a FormatException. Use tryParse.
• Joining many strings with + in a loop. Use a StringBuffer instead, as shown in Strings.

Try it yourself

Write a program that takes ' hello WORLD from dart ' and prints:

1. the text trimmed and in title case: Hello World From Dart
2. how many words it has: 4
3. the words joined with - in lower case: hello-world-from-dart