An 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.

Implemented by



Creates a Map instance with the default implementation, LinkedHashMap.

Map.from(Map other)

Creates a LinkedHashMap instance that contains all key-value pairs of other.

Map.fromIterable(Iterable iterable, { K key(element), V value(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 instance associating the given keys to values.


Creates an identity map with the default implementation, LinkedHashMap.

Map.unmodifiable(Map other)

Creates an unmodifiable hash based map containing the entries of other.



hashCode int

Get a hash code for this object.

read-only, inherited
isEmpty bool

Returns true if there is no key-value pair in the map.

isNotEmpty bool

Returns true if there is at least one key-value pair in the map.

keys Iterable<K>

The keys of this.

length int

The number of key-value pairs in the map.

runtimeType Type

A representation of the runtime type of the object.

read-only, inherited
values Iterable<V>

The values of this.



operator ==(other) bool

The equality operator.

operator [](Object key) → V

Returns 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.


addAll(Map<K, V> other) → void

Adds all key-value pairs of other to this map.

clear() → void

Removes all pairs from the map.

containsKey(Object key) bool

Returns true if this map contains the given key.

containsValue(Object value) bool

Returns true if this map contains the given value.

forEach(void f(K key, V value)) → void

Applies f to each key-value pair of the map.

noSuchMethod(Invocation invocation) → dynamic

Invoked when a non-existent method or property is accessed.

putIfAbsent(K key, V ifAbsent()) → V

Look up the value of key, or add a new value if it isn't there.

remove(Object key) → V

Removes key and its associated value, if present, from the map.

toString() String

Returns a string representation of this object.