Dart ListQueue
last modified April 4, 2025
In Dart, ListQueue is an efficient list-based implementation of the Queue interface. It provides O(1) operations for adding/removing at both ends.
ListQueue combines benefits of both lists and queues. It supports index-based access like lists while maintaining efficient queue operations.
Creating a ListQueue
We can create a ListQueue using its constructor or from an existing iterable.
import 'dart:collection';
void main() {
var queue = ListQueue<String>();
queue.add('apple');
queue.add('banana');
queue.add('orange');
print(queue);
}
This creates an empty ListQueue and adds three elements. The generic type parameter specifies the element type as String.
$ dart main.dart
{apple, banana, orange}
Adding Elements
ListQueue provides multiple methods for adding elements at different positions.
import 'dart:collection';
void main() {
var queue = ListQueue.of([1, 2, 3]);
// Add to end
queue.add(4);
// Add to start
queue.addFirst(0);
// Add multiple
queue.addAll([5, 6]);
print(queue);
}
We demonstrate adding elements to both ends of the queue. addFirst is particularly useful for queue operations.
$ dart main.dart
{0, 1, 2, 3, 4, 5, 6}
Removing Elements
ListQueue provides several ways to remove elements from the collection.
import 'dart:collection';
void main() {
var queue = ListQueue.of(['a', 'b', 'c', 'd', 'e']);
// Remove first
var first = queue.removeFirst();
// Remove last
var last = queue.removeLast();
// Remove specific element
queue.remove('c');
print('Removed: $first, $last');
print('Remaining: $queue');
}
This shows FIFO (removeFirst) and LIFO (removeLast) operations. The remove method deletes the first occurrence of the specified value.
$ dart main.dart
Removed: a, e
Remaining: {b, d}
Accessing Elements
ListQueue supports both queue-style access and index-based element retrieval.
import 'dart:collection';
void main() {
var queue = ListQueue.of([10, 20, 30, 40, 50]);
// Peek first/last
print('First: ${queue.first}');
print('Last: ${queue.last}');
// Index access
print('Element at 2: ${queue.elementAt(2)}');
// Iteration
print('All elements:');
for (var item in queue) {
print(item);
}
}
ListQueue maintains list-like characteristics while providing queue operations. We can access elements by position or iterate through them.
$ dart main.dart First: 10 Last: 50 Element at 2: 30 All elements: 10 20 30 40 50
Queue Operations
ListQueue implements standard queue operations with efficient performance.
import 'dart:collection';
void main() {
var queue = ListQueue<int>();
// Enqueue elements
queue.addLast(1);
queue.addLast(2);
queue.addLast(3);
// Dequeue elements
while (queue.isNotEmpty) {
print('Processing: ${queue.removeFirst()}');
}
print('Queue empty: ${queue.isEmpty}');
}
This demonstrates classic FIFO queue behavior. Elements are added at the end and removed from the front. The isNotEmpty check is safer than checking length.
$ dart main.dart Processing: 1 Processing: 2 Processing: 3 Queue empty: true
Best Practices
- Queue vs List: Use ListQueue when you need both queue operations and index access.
- Capacity: Consider initial capacity for large queues to reduce reallocations.
- Bulk Operations: Use addAll for adding multiple elements efficiently.
- Type Safety: Always specify generic type parameters for type safety.
Source
This tutorial covered Dart's ListQueue with practical examples demonstrating its key features and usage patterns for efficient queue operations.
Author
List all Dart tutorials.