Map operations

Learn Map management with [] and .putIfAbsent.

Map operations

Read a value from a Map with square brackets: ages['Ayşe'] returns the value for 'Ayşe', or null if it is missing. Adding a pair uses the same syntax: ages['Cem'] = 26;.

putIfAbsent places a value only when the key is absent: ages.putIfAbsent('Deniz', () => 30);. If the key exists it does nothing; otherwise it calls the given function and stores the result.

Use remove to delete and entries to see all pairs. length reports the count. Because the [] operator returns null for a missing key, null safety matters here; the next group dives into that.

putIfAbsent vs update

putIfAbsent only sets a value when the key is absent; if present, it leaves it untouched. update changes the existing value; if the key is missing it may throw or compute a default.

For example ages.putIfAbsent('Cem', () => 25); sets 25 when 'Cem' is missing. ages.update('Ayşe', (v) => v + 1); increments Ayşe's age by one.

Reach for putIfAbsent on first insert and update when you need to modify. Pick the one that matches your task.

Exercise Phone book

Create an empty Map<String, String>. Use putIfAbsent to add two people: name as key, phone as value. Then print the phone book with print.

Show example solution

void main() {
  var phones = <String, String>{};
  phones.putIfAbsent('Ayşe', () => '555-1000');
  phones.putIfAbsent('Mert', () => '555-2000');
  print(phones);
}

Test yourself

When does putIfAbsent set a value?
- Always
- When the key exists
- Never
- When the key is missing
Show answer

When the key is missing — putIfAbsent only sets a value when the key is absent.

Read a value

void main() {
  var ages = <String, int>{'Ayşe': 28};
  print(ages____);
}

Show answer

void main() {
  var ages = <String, int>{'Ayşe': 28};
  print(ages['Ayşe']);
}

Match the operations

[]

Read or write a value
putIfAbsent

Only set if absent
update

Modify existing
remove

Delete the key

Next lesson: Map iteration

We Are Enhancing Your Experience

Cookie Preferences

Strictly Necessary Cookies

Analytical Cookies