Summary - Collections
- Dart course
- Intermediate
- Lesson 46/116
- 5 min
Combine List, Set and Map to write a phone book.
Summary - Collections
In this group we learned four core collections: List is ordered and allows duplicates; Set holds unique elements; Map stores key-value pairs; Queue works in FIFO order. Their common ancestor is Iterable.
Each collection fits its scenario. List for ordered data, Set for deduplication, Map for fast lookup, Queue for ordered processing. Iterable offers lazy traversal.
Now let's do an exercise that uses them together: create three different collections and print their lengths.
Practice Create three collections
Create a List<int> (3 elements), a Set<int> (2 elements) and a Map<String, int> (2 pairs). Print the length of each on a separate line.
Starter code
void main() {
// create a List, a Set and a Map
// print the length of each
}Sample solution
void main() {
var list = <int>[1, 2, 3];
var set = <int>{4, 5};
var map = <String, int>{'a': 1, 'b': 2};
print(list.length);
print(set.length);
print(map.length);
}Expected output
3 2 2
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match collections to their purpose
| Term | Meaning |
|---|---|
List |
Ordered, duplicates |
Set |
Unique elements |
Map |
Key-value |
Queue |
FIFO order |
2 Which collection stores key-value pairs?
- List
- Map Correct answer
- Queue
- Iterable
Explanation: Map stores key-value pairs.