Map<K, V> class abstract interface

A collection of key/value pairs, from which you retrieve a value using its associated key.

There is a finite number of keys in the map, and each key has exactly one value associated with it.

Maps, and their keys and values, can be iterated. The order of iteration is defined by the individual type of map. Examples:

  • The plain HashMap is unordered (no order is guaranteed),
  • the LinkedHashMap iterates in key insertion order,
  • and a sorted map like SplayTreeMap iterates the keys in sorted order.

It is generally not allowed to modify the map (add or remove keys) while an operation is being performed on the map, for example in functions called during a forEach or putIfAbsent call. Modifying the map while iterating the keys or values may also break the iteration.

It is generally not allowed to modify the equality of keys (and thus not their hashcode) while they are in the map. Some specialized subtypes may be more permissive, in which case they should document this behavior.



Creates an empty LinkedHashMap.
Map.from(Map other)
Creates a LinkedHashMap with the same keys and values as other.
Map.fromEntries(Iterable<MapEntry<K, V>> entries)
Creates a new map and adds all entries.
Map.fromIterable(Iterable iterable, {K key(dynamic element)?, V value(dynamic element)?})
Creates a Map instance in which the keys and values are computed from the iterable.
Map.fromIterables(Iterable<K> keys, Iterable<V> values)
Creates a map associating the given keys to the given values.
Creates an identity map with the default implementation, LinkedHashMap.
Map.of(Map<K, V> other)
Creates a LinkedHashMap with the same keys and values as other.
Map.unmodifiable(Map other)
Creates an unmodifiable hash-based map containing the entries of other.


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


addAll(Map<K, V> other) → void
Adds all key/value pairs of other to this map.
addEntries(Iterable<MapEntry<K, V>> newEntries) → void
Adds all key/value pairs of newEntries to this map.
cast<RK, RV>() Map<RK, RV>
Provides a view of this map as having RK keys and RV instances, if necessary.
clear() → void
Removes all entries from the map.
containsKey(Object? key) bool
Whether this map contains the given key.
containsValue(Object? value) bool
Whether this map contains the given value.
forEach(void action(K key, V value)) → void
Applies action to each key/value pair of the map.
map<K2, V2>(MapEntry<K2, V2> convert(K key, V value)) Map<K2, V2>
Returns a new map where all entries of this map are transformed by the given convert function.
noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent method or property is accessed.
putIfAbsent(K key, V ifAbsent()) → V
Look up the value of key, or add a new entry if it isn't there.
remove(Object? key) → V?
Removes key and its associated value, if present, from the map.
removeWhere(bool test(K key, V value)) → void
Removes all entries of this map that satisfy the given test.
toString() String
A string representation of this object.
update(K key, V update(V value), {V ifAbsent()?}) → V
Updates the value for the provided key.
updateAll(V update(K key, V value)) → void
Updates all values.


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

Static Methods

castFrom<K, V, K2, V2>(Map<K, V> source) Map<K2, V2>
Adapts source to be a Map<K2, V2>.