LinkedHashSet<E> class

A LinkedHashSet is a hash-table based Set implementation.

The default implementation of Set is LinkedHashSet.

The LinkedHashSet also keeps track of the order that elements were inserted in, and iteration happens in first-to-last insertion order.

The elements of a LinkedHashSet must have consistent Object.== and Object.hashCode implementations. This means that the == operator must define a stable equivalence relation on the elements (reflexive, symmetric, transitive, and consistent over time), and that hashCode must be the same for objects that are considered equal by ==.

Iteration of elements is done in element insertion order. An element that was added after another will occur later in the iteration. Adding an element that is already in the set does not change its position in the iteration order, but removing an element and adding it again will make it the last element of an iteration.

Most simple operations on HashSet are done in (potentially amortized) constant time: add, contains, remove, and length, provided the hash codes of objects are well distributed.

Note: Do not modify a set (add or remove elements) while an operation is being performed on that set, for example in functions called during a forEach or containsAll call, or while iterating the set.

Do not modify elements in a way which changes their equality (and thus their hash code) while they are in the set. Some specialized kinds of sets may be more permissive with regards to equality, in which case they should document their different behavior and restrictions.

Example:

final planets = <String>{}; // LinkedHashSet

To add data to a set, use add or addAll.

final uranusAdded = planets.add('Uranus'); // true
planets.addAll({'Venus', 'Mars', 'Earth', 'Jupiter'});
print(planets); // {Uranus, Venus, Mars, Earth, Jupiter}

To check if the set is empty, use isEmpty or isNotEmpty. To find the number of elements in the set, use length.

print(planets.isEmpty); // false
print(planets.length); // 5

To check whether the set has an element with a specific value, use contains.

final marsExists = planets.contains('Mars'); // true

The forEach method calls a function with each element of the set.

planets.forEach(print);
// Uranus
// Venus
// Mars
// Earth
// Jupiter

To make a copy of the set, use toSet.

final copySet = planets.toSet();
print(copySet); // {Uranus, Venus, Mars, Earth, Jupiter}

To remove an element, use remove.

final removedValue = planets.remove('Mars'); // Mars
print(planets); // {Uranus, Venus, Earth, Jupiter}

To remove multiple elements at the same time, use removeWhere or removeAll.

planets.removeWhere((element) => element.startsWith('E'));
print(planets); // {Uranus, Venus, Jupiter}

To removes all elements in this set that do not meet a condition, use retainWhere.

planets.retainWhere((element) => element.contains('Jupiter'));
print(planets); // {Jupiter}
```dart continued
To remove all elements and empty the set, use [clear].
```dart continued
planets.clear();
print(planets.isEmpty); // true
print(planets); // {}

See also:

• Set is the general interface of collection where each object can occur only once.
• HashSet the order of the objects in the iteration is not guaranteed.
• SplayTreeSet iterates the objects in sorted order.