Dart HashMap explanation with examples

Introduction to HashMap<K,V> class in Dart:

The HashMap class can be used to store key-value pairs. We can use the keys to access and modify its values.

The keys of a HashMap can be any object but they should implement the Object.== and Object.hashCode methods.

The HashMap is an unordered implementation. So the iteration doesn’t follow any order. If the map is modified, the iteration order changes.

Constructors of HashMap:

We can create a HashMap in different ways. Following are the constructors available:

HashMap({bool equals(K, K)?, int hashCode(K)?, bool isValidKey(dynamic)?})

This constructor creates a HashMap.

HashMap.from(Map o)

Create one HashMap from another Map o with the same key-value pairs.

HashMap.fromEntries(Iterable<MapEntry<K, V>> e)

Create one HashMap from the given iterable entries.

HashMap.fromIterable(Iterable iterable, {K key(dynamic element)?, V value(dynamic element)?})

Creates one HashMap from the Iterable.

HashMap.fromIterables(Iterable k, Iterable v)

Creates a HashMap associating the keys k to values v.

HashMap.identity()

Creates an unordered identity-based map.

HashMap.of(Map<K, V> o)

Create one HashMap containing the key-value pairs of the Map o.

Properties of HashMap:

Following properties are available in a dart HashMap:

entries → Iterable<MapEntry<K, V>>

It is the entries of this HashMap.

hashCode → int

It holds the hash code.

isEmpty → bool

It is a boolean value, true if the HashMap is empty, false otherwise.

isNotEmpty → bool

It is the opposite of isEmpty.

keys → Iterable

It is the keys of the HashMap.

length → int

Length of the HashMap.

values → Iterable

The values of the HashMap.

runtimeType → Type

Runtime type of the HashMap.

Methods of HashMap:

Following methods are available for a HashMap:

containsKey(Object? k) → bool

Checks if the key k is in the HashMap or not.

addAll(Map<K, V> m) → void

This method adds all the key-value pairs of another map m to the current HashMap.

containsValue(Object? v) → bool

Check if the value v is in the HashMap or not.

addEntries(Iterable<MapEntry<K, V>> e) → void

Add the key-value pairs of the entries e to the HashMap.

forEach(void f(K k, V v)) → void

Use the function f on each item of the HashMap.

cast<RK, RV>() → Map<RK, RV>

Get a view of this map.

map<K2, V2>(MapEntry<K2, V2> convert(K k, V v)) → Map<K2, V2>

It converts the current HashMap to a new Map by using the given convert function.

update(K k, V update(V v), {V ifAbsent()?}) → V

It updates the value v for the key k.

clear() → void

It removes all items from the HashMap.

noSuchMethod(Invocation i) → dynamic

This method is invoked when we try to access any invalid method or property of the HashMap.

updateAll(V update(K k, V v)) → void

This method updates all values.

putIfAbsent(K k, V ifAbsent()) → V

It checks for the key k in the HashMap and adds it if not found.

remove(Object? k) → V?

It removes the pair with key k from the HashMap if found in the HashMap.

removeWhere(bool f(K k, V v)) → void

It removes all pairs from a map for those the function f returns true.

toString() → String

Get the string representation.

Reference:

HashMap class Flutter doc

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