StringBuffer

Learn efficient string concatenation with StringBuffer.

StringBuffer

Joining many strings with + creates a new string each time, so it is slow in loops. StringBuffer builds a mutable string that grows in place. You write to it and at the end call toString() for the final string. The difference is large when you join hundreds of pieces in a loop.

Example: final sb = StringBuffer(); sb.write("a"); sb.write("b"); print(sb.toString());. writeln adds a newline after each piece. clear empties it. isEmpty tells you if it has content. Ideal for accumulation tasks.

Exercise Your turn: build with StringBuffer

Create a StringBuffer and use a for loop to add the numbers 0 through 2 separated by commas. Get the result with toString() and print it.

Show example solution

void main() {
  final sb = StringBuffer();
  for (var i = 0; i < 3; i++) {
    if (i > 0) sb.write(",");
    sb.write(i.toString());
  }
  print(sb.toString());
}

write and writeln

write appends a single piece; writeln also adds a newline character after each call. If you are building a log file and want each entry on its own line you use writeln. writeAll takes a list and writes each element separated by a delimiter you choose; similar to join but into a StringBuffer.

To empty the buffer call clear. The length property gives the current character count. isEmpty and isNotEmpty check fullness. clear is handy when you want to reuse a buffer.

Test yourself

Create a StringBuffer

final sb = ____();

Show answer

final sb = StringBuffer();

Most efficient method to join many strings?
```
final sb = StringBuffer();
for (var i = 0; i < 1000; i++) {
  sb._____(i.toString());
}
```
- write
- concat
- addAll
- append
Show answer

write — write appends to a StringBuffer.
Match StringBuffer

write

appends one piece
writeln

appends with newline
writeAll

appends a list
clear

empties the buffer

Next lesson: Summary - Advanced strings

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