A map is a collection of key/value pairs. The value is retrieved from a map with its associated key. Maps are also called dictionaries, associative arrays, or hash tables.

Depending on the iteration order, there are three types of maps in Dart:

• HashMap - unordered

• LinkedHashMap - ordered by insertion order

• SplayTreeMap - ordered by sorted keys

By default, creating an instance using Map constructor (Map, Map.from, or Map.of) creates a LinkedHashMap.

A map is created with a map literal or with a map constructor. To work with maps, we import the dart:collection library.

A map literal consists of a pair of curly brackes, in which we specify the key/value pairs. The pairs are separated by comma. The key is separated from the value by colon.

Maps can be declared in two ways −

• Using Map Literals

• Using a Map constructor

Declaring a Map using Map Literals

To declare a map using map literals, you need to enclose the key-value pairs within a pair of curly brackets "{ }".

Here is its syntax −

var identifier = { key1:value1, key2:value2 [,…..,key_n:value_n] }

Declaring a Map using a Map Constructor

To declare a Map using a Map constructor, we have two steps. First, declare the map and second, initialize the map.

The syntax to declare a map is as follows −

var identifier = new Map()

Now, use the following syntax to initialize the map −

map_name[key] = value

Example: Map Literal

void main() { 
   var details = {'Usrname':'tom','Password':'pass@123'}; 
   print(details); 
}

It will produce the following output −

{Usrname: tom, Password: pass@123}

Example: Adding Values to Map Literals at Runtime

void main() { 
   var details = {'Usrname':'tom','Password':'pass@123'}; 
   details['Uid'] = 'U1oo1'; 
   print(details); 
}

It will produce the following output −

{Usrname: tom, Password: pass@123, Uid: U1oo1}

Example: Map Constructor

void main() { 
   var details = new Map(); 
   details['Usrname'] = 'admin'; 
   details['Password'] = 'admin@123'; 
   print(details); 
}

It will produce the following output −

{Usrname: admin, Password: admin@123}

Note − A map value can be any object including NULL.

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