Dart StringBuffer

last modified January 28, 2024

In this article we show how to concatenate strings efficiently in Dart language using StringBuffer class.

A string is a sequence of UTF-16 code units. It is used to represent some text in a program.

StringBuffer is a class that is used to create new strings efficiently by concatenation. It contains write, writeAll, writeln and clear member functions for string manipulation.

Dart StringBuffer simple example

The following is a simple Dart program which uses StringBuffer;

main.dart

void main() { var msg = StringBuffer(‘There are’); msg.write(’ three ‘); msg.writeAll([‘hawks’, ‘in’, ’the sky’], " “);

String output = msg.toString(); print(output); }

The program dynamically builds a new string and prints it to the console.

var msg = StringBuffer(‘There are’);

We create a new instance of StringBuffer. We add some initial text.

msg.write(’ three ‘);

We insert another string with write.

msg.writeAll([‘hawks’, ‘in’, ’the sky’], " “);

We insert multiple strings with writeAll. The first parameter is a list of strings, the second parameter is a separator character.

String output = msg.toString();

Finally, we turn the string buffer into a single string with toString.

$ dart main.dart There are three hawks in the sky

Dart StringBuffer writeln

The writeln method writes a new string followed by a newline character.

main.dart

void main() { var msg = StringBuffer(‘blue sky\n’); msg.writeln(‘old owl’); msg.writeln(’lonely wolf’); msg.writeln(‘strict regime’);

print(msg.length); print(msg.toString()); }

The example creates a string consisting of several lines of text data. In addition, we print the size of the text in characters using length.

$ dart main.dart 43 blue sky old owl lonely wolf strict regime

Dart StringBuffer isEmpty

We can check if a string buffer is empty with isEmpty. The buffer can be deleted with clear.

main.dart

void main() { var msg = StringBuffer(); check(msg); msg.writeAll([‘an’, ‘old’, ‘hawk’, ‘in’, ’the’, ‘sky’], ’ ‘); check(msg); print(msg.toString()); msg.clear(); check(msg); }

void check(StringBuffer msg) { if (msg.isEmpty) { print(’the buffer is empty’); } else { print(’the buffer is not empty’); } }

In the program, we build a string with StringBuffer and use the isEmpty method to check, if the buffer is empty.

$ dart main.dart the buffer is empty the buffer is not empty an old hawk in the sky the buffer is empty

Source

Dart StringBuffer - language reference

In this article we have covered the StringBuffer class in Dart.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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