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.

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.

Implemented by

Constructors

Map()
Creates a Map instance with the default implementation, LinkedHashMap. [...]
factory
Map.from(Map other)
Creates a LinkedHashMap instance that contains all key-value pairs of other. [...]
factory
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. [...]
factory
Map.fromIterables(Iterable<K> keys, Iterable<V> values)
Creates a Map instance associating the given keys to values. [...]
factory
Map.identity()
Creates an identity map with the default implementation, LinkedHashMap. [...]
factory
Map.unmodifiable(Map other)
Creates an unmodifiable hash based map containing the entries of other. [...]
factory

Properties

isEmpty bool
Returns true if there is no key-value pair in the map.
read-only
isNotEmpty bool
Returns true if there is at least one key-value pair in the map.
read-only
keys Iterable<K>
The keys of this. [...]
read-only
length int
The number of key-value pairs in the map.
read-only
values Iterable<V>
The values of this. [...]
read-only
hashCode int
The hash code for this object. [...]
read-only, inherited
runtimeType Type
A representation of the runtime type of the object.
read-only, inherited

Methods

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. [...]
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. [...]
noSuchMethod(Invocation invocation) → dynamic
Invoked when a non-existent method or property is accessed. [...]
inherited
toString() String
Returns a string representation of this object.
inherited

Operators

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. [...]
operator ==(other) bool
The equality operator. [...]
inherited