Dart StringBuffer

last modified February 1, 2023

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;

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.

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.

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

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

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