Dart DoubleLinkedQueueEntry

last modified April 4, 2025

In Dart, DoubleLinkedQueueEntry represents an element in a DoubleLinkedQueue. It provides links to adjacent elements and methods to manipulate queue position.

Each entry contains a value and maintains references to the next and previous entries. This enables efficient insertion and removal operations at any position.

Basic DoubleLinkedQueueEntry Usage

Let’s start with basic usage of DoubleLinkedQueueEntry to understand its role.

main.dart

import ‘dart:collection’;

void main() { var queue = DoubleLinkedQueue<String>(); queue.add(‘Apple’); queue.add(‘Banana’); queue.add(‘Cherry’);

// Get first entry var firstEntry = queue.firstEntry(); print(‘First value: ${firstEntry!.value}’);

// Get next entry var nextEntry = firstEntry.nextEntry(); print(‘Next value: ${nextEntry!.value}’);

// Get previous from next (should be first) var prevEntry = nextEntry.previousEntry(); print(‘Previous value: ${prevEntry!.value}’); }

This example demonstrates basic navigation between queue entries. We access the first entry, then its next entry, and verify we can navigate back.

$ dart main.dart First value: Apple Next value: Banana Previous value: Apple

Inserting Elements Using Entries

DoubleLinkedQueueEntry allows inserting elements relative to existing entries.

main.dart

import ‘dart:collection’;

void main() { var queue = DoubleLinkedQueue<String>(); queue.add(‘Apple’); queue.add(‘Cherry’);

// Get first entry var firstEntry = queue.firstEntry();

// Insert before first entry firstEntry!.insertBefore(‘Apricot’);

// Insert after first entry firstEntry.insertAfter(‘Banana’);

print(queue); }

We insert elements before and after existing entries. This provides precise control over queue positioning without needing indexes.

$ dart main.dart {Apricot, Apple, Banana, Cherry}

Removing Elements Using Entries

Entries can remove themselves from the queue while maintaining structure.

main.dart

import ‘dart:collection’;

void main() { var queue = DoubleLinkedQueue<String>(); queue.addAll([‘Apple’, ‘Banana’, ‘Cherry’, ‘Date’]);

// Get second entry var secondEntry = queue.firstEntry()!.nextEntry();

// Remove the entry var removedValue = secondEntry!.remove();

print(‘Removed: $removedValue’); print(‘Remaining queue: $queue’); }

The remove() method removes the entry from the queue and returns its value. The queue automatically updates its links to maintain continuity.

$ dart main.dart Removed: Banana Remaining queue: {Apple, Cherry, Date}

Iterating Through Entries

We can traverse the queue using entry navigation methods.

main.dart

import ‘dart:collection’;

void main() { var queue = DoubleLinkedQueue<int>(); queue.addAll([10, 20, 30, 40, 50]);

// Start with first entry var current = queue.firstEntry();

print(‘Forward traversal:’); while (current != null) { print(current.value); current = current.nextEntry(); }

// Start with last entry current = queue.lastEntry();

print(’\nBackward traversal:’); while (current != null) { print(current.value); current = current.previousEntry(); } }

This demonstrates bidirectional traversal of the queue using entry navigation. We can move forward or backward through the linked structure.

$ dart main.dart Forward traversal: 10 20 30 40 50

Backward traversal: 50 40 30 20 10

Advanced Entry Manipulation

Entries can be used for complex queue manipulations like reordering.

main.dart

import ‘dart:collection’;

void main() { var queue = DoubleLinkedQueue<String>(); queue.addAll([‘A’, ‘B’, ‘C’, ‘D’, ‘E’]);

// Get middle entry var middle = queue.firstEntry()!.nextEntry()!.nextEntry();

// Remove and reinsert at beginning middle!.remove(); queue.firstEntry()!.insertBefore(middle.value);

print(‘After moving middle to front: $queue’);

// Swap first and last var firstVal = queue.firstEntry()!.value; var lastVal = queue.lastEntry()!.value;

queue.firstEntry()!.value = lastVal; queue.lastEntry()!.value = firstVal;

print(‘After swapping first and last: $queue’); }

This shows advanced manipulation of queue elements using entries. We move an element and swap values directly through entry references.

$ dart main.dart After moving middle to front: {C, A, B, D, E} After swapping first and last: {E, A, B, D, C}

Best Practices

• Null Safety: Always check for null when navigating entries.

• Performance: Entry operations are O(1) for adjacent access.

• Concurrency: Queue entries aren’t thread-safe by default.

• Memory: Each entry maintains references, increasing memory use.

Source

Dart DoubleLinkedQueueEntry Documentation

This tutorial covered Dart’s DoubleLinkedQueueEntry with practical examples demonstrating its key features and usage patterns.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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