Learn All About Collections in Salesforce: List, Set and Map

In this Blog, we will study collections in Salesforce.

List

It is an ordered collection of elements. Each element of the list has a unique index and the index of the first element of the list always starts with 0.

The list can be nested and multi-dimensional.

List elements can be a primitive, collection, sObject, User-defined types, and built-in types.

Example:

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

List Methods

To add records in list - mylist.add(‘a’);
To get a particular index value Integer i = mylist.get(0);
To add value at any particular index – mylist.add(1,30);
To clean or clear list – mylist.clear();
To check the size of the list – Integer s = mylist.size();
To check the list is empty or not – Boolean b = mylist.isEmpty();
To add values of a list into another list – mylist.addAll(fromList);
To add values from a set into list – mylist.addAll(fromSet);
To clone a list – mylist.clone();
To check if a value is available inside the list – mylist.contains(‘value’); (This returns a boolean value).
To compare two lists – mylist.equals(list2);

System.debug(‘List Contains...’ + mylist);

Don't forget to check out: Mastering Apex Collections | Salesforce Tutorial

Set

An unordered collection of elements and it does not contain duplicate elements.

It can be nested and elements of a set can be – primitive, collection, sObject, user-defined type and built-in type.

Example:

Set<String> myset = new Set<String>();

Set Methods

To remove from set – myset.remove(20);
To check if set is empty – isEmpty();
To retain set elements – retainAll(setofElementsToRetain);

Map

A map is a collection of key-value pairs. Keys are always unique whereas values can be duplicated. In apex, we use the hash structure for all maps. Map key and value can be nested and can contain any collection such as primitive type, collection, sObject, user-defined types, and built-in type.

Example:

Map<String, String> mymap = new Map<String, String>();