Home SALESFORCEAPEX Types of Collections in APEX

Apex has the following types of collections:

S.No Collection Name Description Example
1 List Ordered collection

of typed primitives,

sObjects, objects,

or collections that

are distinguished by

their indices


// Create an empty list of String

List<String> my_list = new



String x = my_list.get(0);

// Create list of records from a query

List<Account> accs = [SELECT Id, Name


Account LIMIT 1000];

2 Map Collection of key-value

pairs where

each unique key

maps to a single

value. Keys can be

any primitive data

type, while values

can be a primitive,

sObject, collection

type, or an object.

Map<String, String> mys = new Map<String,


Map<String, String> mys = new Map<String,

String>{‘a’ => ‘b’, ‘c’ => ‘d’.


Account myAcct = new Account();

Map<Integer, Account> m = new

Map<Integer, Account>();

m.put(1, myAcct);

3 Set Unordered collection

that doesn’t contain

any duplicate

elements.  Set elements can be of any data type—primitive types, collections, sObjects, user-defined types, and built-in Apex types

Set<Integer> s = new Set<Integer>();




s.remove(1)   //Remove the element from the set


Note: There is no limit on the number of items a collection can hold. However, there is a general limit on heap size.

Total heap size is 6 MB.

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