Map

The Map object is a simple key/value pair. Keys and values in a map may be of any type. A Map is a dynamic collection. In other words, Maps can grow and shrink at runtime.

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.

Map – Properties

The Map class in the dart:core package defines the following properties −

Sr.No	Property & Description
1	KeysReturns an iterable object representing keys
2	ValuesReturns an iterable object representing values
3	LengthReturns the size of the Map
4	isEmptyReturns true if the Map is an empty Map
5	isNotEmptyReturns true if the Map is an empty Map

Map – Functions

Following are the commonly used functions for manipulating Maps in Dart.

Sr.No	Function Name & Description
1	addAll()Adds all key-value pairs of other to this map.
2	clear()Removes all pairs from the map.
3	remove()Removes key and its associated value, if present, from the map.
4	forEach()Applies f to each key-value pair of the map.