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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.

Practice 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.

Starter code

main.dart
void main() {
  // Create a StringBuffer
  // Loop 0,1,2 with commas
  // Print with toString()
}

Sample solution

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

Expected output

0,1,2

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.

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Create a StringBuffer

Question 
final sb = ____();
Answer 
final sb = StringBuffer();

Explanation: StringBuffer() creates an empty buffer.

2 Most efficient method to join many strings?

main.dart
final sb = StringBuffer();
for (var i = 0; i < 1000; i++) {
  sb._____(i.toString());
}
  • write Correct answer
  • concat
  • addAll
  • append

Explanation: write appends to a StringBuffer.

3 Match StringBuffer

Term Meaning
write appends one piece
writeln appends with newline
writeAll appends a list
clear empties the buffer

All lessons in Beginner

1 Dart basics

  1. What is Dart?
  2. Your first program
  3. dart run
  4. Comments
  5. String interpolation
  6. Summary - Dart basics

2 Variables

  1. var and type
  2. final
  3. const
  4. late
  5. Null safety
  6. Summary - Variables

3 Data types

  1. Integer types
  2. Floating-point types
  3. bool and String
  4. Type inference
  5. dynamic
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add and subtract
  3. Multiply and divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic operators
  2. Assignment operators
  3. Comparison operators
  4. Logical operators
  5. Null-aware operators
  6. Summary - Operators

6 Strings

  1. Creating strings
  2. String interpolation
  3. length and methods
  4. substring
  5. contains and indexOf
  6. Summary - Strings

7 Conditionals

  1. The if statement
  2. else and else if
  3. switch
  4. Pattern matching
  5. Ternary
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. The while loop
  3. The do-while loop
  4. for-in
  5. break and continue
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Listing the cart
  5. Putting it together

10 Lists

  1. Creating lists
  2. List access
  3. add and remove
  4. length and contains
  5. List methods
  6. Summary - Lists

11 Sets and Maps

  1. Set
  2. Set operations
  3. Map
  4. Map operations
  5. Map iteration
  6. Summary - Sets and Maps

12 Functions

  1. Defining functions
  2. Return values
  3. Arrow functions
  4. Optional parameters
  5. First-class functions
  6. Summary - Functions

13 Null safety in depth

  1. Nullable types
  2. Null-aware operators
  3. The ! operator
  4. late
  5. Null check
  6. Summary - Null safety

14 Class basics

  1. class
  2. Constructor
  3. Instance variables
  4. Methods
  5. this
  6. Summary - Class basics

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Advanced string operations

  1. split and join
  2. replace
  3. trim and pad
  4. RegExp
  5. StringBuffer
  6. Summary - Advanced strings

17 Enums

  1. Defining enums
  2. Enum values
  3. Enhanced enums
  4. switch with enum
  5. Enum and patterns
  6. Summary - Enums

18 Exceptions

  1. try/catch
  2. throw
  3. finally
  4. The Exception class
  5. on clause
  6. Summary - Exceptions

19 Async basics

  1. Future
  2. async/await
  3. then
  4. Future.error
  5. Future.wait
  6. Summary - Async basics

20 Beginner final

  1. Project design
  2. Classes
  3. Collections
  4. Error handling
  5. Putting it together