HashMap<K, V> class

A custom implementation of a hash map that implements the Map<K, V> interface.

This map uses open addressing with chaining to resolve hash collisions. Each bucket holds a list of _HashMapEntry<K, V> objects, allowing multiple entries to exist in the same bucket if they hash to the same index.

It supports automatic resizing when the load factor exceeds 0.75, ensuring performance remains optimal as the number of entries grows.

This is useful for educational purposes or when custom behavior is required beyond what dart:collection offers.

βš™οΈ Internal Design:

  • Backed by an array of lists: List<List<_HashMapEntry<K, V>>?> _buckets
  • On collision: new entries are appended to the appropriate list
  • Resize logic doubles capacity when load factor exceeds the threshold

πŸ“¦ Example Usage:

final map = HashMap<String, int>();
map['apple'] = 3;
map['banana'] = 5;
print(map['apple']); // 3
print(map.containsKey('banana')); // true
print(map.length); // 2
Implemented types
Implementers
Available extensions
Annotations

Constructors

HashMap()
A custom implementation of a hash map that implements the Map<K, V> interface.
HashMap.from(Map<K, V> map)
Creates a hash map from an existing map.
factory

Properties

entries β†’ Iterable<MapEntry<K, V>>
The map entries of this Map.
no setteroverride
hashCode β†’ int
The hash code for this object.
no setterinherited
isEmpty β†’ bool
Whether there is no key/value pair in the map.
no setteroverride
isNotEmpty β†’ bool
Whether there is at least one key/value pair in the map.
no setteroverride
keys β†’ Iterable<K>
The keys of this Map.
no setteroverride
length β†’ int
The number of key/value pairs in the map.
no setteroverride
runtimeType β†’ Type
A representation of the runtime type of the object.
no setterinherited
values β†’ Iterable<V>
The values of this Map.
no setteroverride

Methods

add(K key, V item) β†’ void

Available on Map<K, V>, provided by the MapExtensions extension

Add item
addAll(Map<K, V> other) β†’ void
Adds all key/value pairs of other to this map.
override
addEntries(Iterable<MapEntry<K, V>> newEntries) β†’ void
Adds all key/value pairs of newEntries to this map.
override
asJson({String delimiter = '_'}) β†’ Map<String, dynamic>

Available on Map<K, V>, provided by the MapExtensions extension

Converts a Map to JSON with formatted keys (_, -, or camelCase).
cast<RK, RV>() β†’ Map<RK, RV>
Provides a view of this map as having RK keys and RV instances, if necessary.
override
clear() β†’ void
Removes all entries from the map.
override
computeIfAbsent(K key, V ifAbsent(K key)) β†’ V

Available on Map<K, V>, provided by the MapExtensions extension

Computes a value for the given key if it is not already present in the map.
containsKey(Object? key) β†’ bool
Whether this map contains the given key.
override
containsValue(Object? value) β†’ bool
Whether this map contains the given value.
override
forEach(void action(K key, V value)) β†’ void
Applies action to each key/value pair of the map.
override
get(K key) β†’ V?

Available on Map<K, V>, provided by the MapExtensions extension

Get value by key
map<K2, V2>(MapEntry<K2, V2> convert(K key, V value)) β†’ Map<K2, V2>
Returns a new map where all entries of this map are transformed by the given convert function.
override
mapKeys<K2>(K2 convert(K key)) β†’ Map<K2, V>

Available on Map<K, V>, provided by the MapExtensions extension

Applies a transformation function to the keys of the Map.
merge(Map<K, V> other) β†’ Map<K, V>

Available on Map<K, V>, provided by the MapExtensions extension

Merges another Map into the current Map, overriding duplicate keys.
noSuchMethod(Invocation invocation) β†’ dynamic
Invoked when a nonexistent method or property is accessed.
inherited
put(K key, V value) β†’ void

Available on Map<K, V>, provided by the MapExtensions extension

Add item
putIfAbsent(K key, V ifAbsent()) β†’ V
Look up the value of key, or add a new entry if it isn't there.
override
remove(Object? key) β†’ V?
Removes key and its associated value, if present, from the map.
override
removeWhere(bool test(K key, V value)) β†’ void
Removes all entries of this map that satisfy the given test.
override
toString() β†’ String
A string representation of this object.
override
update(K key, V update(V value), {V ifAbsent()?}) β†’ V
Updates the value for the provided key.
override
updateAll(V update(K key, V value)) β†’ void
Updates all values.
override

Operators

operator ==(Object other) β†’ bool
The equality operator.
inherited
operator [](Object? key) β†’ V?
The value for the given key, or null if key is not in the map.
override
operator []=(K key, V value) β†’ void
Associates the key with the given value.
override