replace

Learn string modification with replaceAll.

replaceAll

To replace all occurrences inside a string use replaceAll. It returns a new string; the original is untouched. For example "a-b-c".replaceAll("-", "_") gives "a_b_c". Every dash became an underscore.

If you want only the first match replaced there is replaceFirst. The difference matters: replaceAll returns the string unchanged if no match is found; it never throws. So you can use it safely without a guard.

First match vs all

replaceFirst changes only the first match and leaves the rest. "a-a-a".replaceFirst("-", "_") gives "a_a-a". It is useful when you only want to change the first separator in a log line.

replaceAll changes every one: "a-a-a".replaceAll("-", "_") gives "a_a_a". Which one to pick depends on the task. Most of the time replaceAll is what you want, like cleaning spaces in a username all at once. Still, you should know both.

Exercise Your turn: replaceAll

Replace every comma in "book,pen,notebook" with ";" and print the result with print.

Show example solution

void main() {
  final list = "book,pen,notebook";
  print(list.replaceAll(",", ";"));
}

Test yourself

The replaceAll call

final fixed = "a-b-c".____("-", "_");

Show answer

final fixed = "a-b-c".replaceAll("-", "_");

Which call turns all dashes of "a-a-a" into underscores?
```
final out = "a-a-a"._____("-", "_");
```
- replaceFirst
- replaceAll
- split
- join
Show answer

replaceAll — replaceAll turns every dash into an underscore.
Match the replace methods

replaceAll

changes every match
replaceFirst

changes only the first
replace

uses a Map
replaceAllMapped

transforms with a function

Next lesson: trim and pad

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