Salesforce Collections

Collections are the group of similar types. There are three types of Salesforce collections. They are

  • List
  • Set
  • Map


List is an ordered collection of elements which will allow duplicates. A list is an ordered collection of typed primitives SObjects, user-defined objects, Apex objects or collections that are distinguished by their includes.

  • The index position of the first element in a lsit is always ‘0’.
  • To declare a list, use the list. keyword followed by the primitive data, SObject, nested list, map, or set type within <>characters.


List<datatype> listName = new List<datatype>();

where datatype allows both primitive datatypes and non-primitive datatypes.

The size of a list changes dynamically when items are added to the list or removed from the list.

List Methods


list.add() method adds the values (items) to the list.

List<String> colors =new List<String>();

or, you can add the items in a single statement as shown below:

List<String> colors =new List<String>{'Red','White','Black'}


list.get(index) retrieves value from list present at index position.

String getcolor = colors.get(1); // we get the value is 'White' in to getcolor veriable.


list.set(index, value) replaces a former value with the specified value at the given index.

colors.set(1,'Green'); // List has value at index ' 1 ' is White is changed to Green.


list.size() return the number of elements in the list.

colors.size(); // Gives the size of colors list is '2'


Remove the elements from the list.


Example Inserting 100 contacts in contacts object

public class ContactInsertion {
	List<contact> contactList = new List<contact>();
	public void methodName() {
		for(integer i=0; i<100 ; i++ ) {
			contact cont = new contact(lastname = 'contact' + i);
			contactList .add(cont);
		insert contactList ;

Go through this reference for the more list methods.


Set is an unordered collection of elements which will not allow duplicates. A set is an unordered collection of primitives or SObjects that do not contain any duplicate elements.To declare a set, use the set keyword followed by the primitive data type name within < > characters


Set<datatype> setName = new Set<datatype>();
  • data type allows only primitive datatypes and SObjects.
  • We cannot get the retrieve the data based on index because set does not  have index.

Go through this reference, for the all variations of set methods.


set <string> s= new set < string > ();

To access elements in a set use the system methods provided by Apex.

<Integer> s=new set <Integer>(); => Define a new set
S.add (1);                       => Adding an element to the set
Boolean b= s.contains(1);        => It will returns true when the element‘1’ contains within the set.
s.remove (1);                    => Remove the element from the set.


Map stores key-value pairs. A map is a collection of key-value pairs where each unique key maps to a single value. Keys can be any primitive datatype while values can be primitive, sobject, collection type or Apex object.

  • To declare a map, use the Map keyword followed by the data types of the value within  < > characters


Map<datatype_key,datatype_value> mapName = new Map<datatype_key,datatype_value>();
  • datatype_key is the storage datatype of key and it allows only primitive datatypes and should be unique.
  • datatype_value is the datatype of value. Both primitive & non-primitive datatypes are allowed. Duplicates are allowed for values.


Map < string, string> m=new map <string, string> ();

Note:-  Similar to lists, map values can contain any collection and can be nested within one another. A map can only contain up to five levels of nested collections inside it.

Map Methods


Insert a key-value pair or replaces a value with the given value for the key.



Retrieves the value for a key.



Retrieves all the keys and return type is set;



Retrieves all the values and return type is list;



Return the number of components in the map.


Example to Create a map of Account Ids and Account objects

public class AccountMapPopulation{

	// Creating map with account id and account object
	map <Id,Account> accountIdMap =new map<Id,Account>();

	public void methodName(){

		// creating the accounts
		account acc1 = new account (name ='account1' , industry = ' Banking');
		account acc2 =new account(name =' account2' , industry = 'Agriculture');
		account acc3 = new account(name='account3' , industry='Banking');

		// populating the map with account id and account object
		accountIdMap .put(,acc1);
		accountIdMap .put(,acc2);
		accountIdMap .put(,acc3);



Go through this reference for the more map methods.