Apex - maps sets and lists - data collections

lists - orders index numbers starting with 0, 1, 2, 3,........

List<string> ListOfCities = new List<string>();

List<string> ListOfStates = new List<string> {'NY', 'LA', 'LV'}();

List<account> AccountToDelete = new List<account> ();//This will be null

List<List<Set<Integer>>> myNestedList = new List<List<Set<Integer>>>();

String [] ListOfStates = new List<string>();

Below are some most frequently used methods.

size()
add()
get()
clear()
set()

//Initialize the List
List<string> ListOfStatesMethod = new List<string>();

//This statement would give null as output in Debug logs
System.debug('Value of List'+ ListOfStatesMethod);

//Add element to the list using add method
ListOfStatesMethod.add('New York');
ListOfStatesMethod.add('Ohio');

//This statement would give New York and Ohio as output in Debug logs
System.debug('Value of List with new States'+ ListOfStatesMethod);

//Get the element at the index 0
String StateAtFirstPosition = ListOfStatesMethod.get(0);

//This statement would give New York as output in Debug log
System.debug('Value of List at First Position'+ StateAtFirstPosition);

//set the element at 1 position
ListOfStatesMethod.set(0, 'LA');

//This statement would give output in Debug log
System.debug('Value of List with element set at First Position'+ ListOfStatesMethod[0]);

//Remove all the elements in List
ListOfStatesMethod.clear();

//This statement would give output in Debug log
System.debug('Value of List'+ ListOfStatesMethod);

sets - unorderd and unique

Set<string> ProductSet = new Set<string>{'Phenol', 'Benzene', 'H2SO4'};
System.debug('Value of ProductSet'+ProductSet);

//Adds an element to the set
//Define set if not defined previously
Set<string> ProductSet = new Set<string>{'Phenol', 'Benzene', 'H2SO4'};
ProductSet.add('HCL');
System.debug('Set with New Value '+ProductSet);

//Removes an element from set
ProductSet.remove('HCL');
System.debug('Set with removed value  '+ProductSet);

//Check whether set contains the particular element or not and returns true or false
ProductSet.contains('HCL');
System.debug('Value of Set with all values '+ProductSet);

maps -unordered- case sensitive -  key value pair

//Initialize the Map
Map<string, string> ProductCodeToProductName = new Map<string, string> {'1000'=>'HCL', '1001'=>'H2SO4'};

//This statement would give as output as key value pair in Debug log
System.debug('value of ProductCodeToProductName'+ProductCodeToProductName);

// Define a new map
Map<string, string> ProductCodeToProductName = new Map<string, string>();

// Insert a new key-value pair in the map where '1002' is key and 'Acetone' is value
ProductCodeToProductName.put('1002', 'Acetone');

// Insert a new key-value pair in the map where '1003' is key and 'Ketone' is value
ProductCodeToProductName.put('1003', 'Ketone');

// Assert that the map contains a specified key and respective value
System.assert(ProductCodeToProductName.containsKey('1002'));
System.debug('If output is true then Map contains the key and output is :'+ProductCodeToProductName.containsKey('1002'));

// Retrieves a value, given a particular key
String value = ProductCodeToProductName.get('1002');
System.debug('Value at the Specified key using get function: '+value);

// Return a set that contains all of the keys in the map
Set SetOfKeys = ProductCodeToProductName.keySet();
System.debug('Value of Set with Keys '+SetOfKeys);