Collections In Salesforce

                                                   Collections

Apex has the following types of collections:

      Lists

      Maps

      Sets

Lists:

A list is an ordered collection of elements that are distinguished by their indices.

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

List will Allow duplicate values.

Syntax:

Syntax

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

• The datatype allows both primitive datatypes and non-primitive datatypes
• Size of the list is dynamically increased.

Sets

Set is an unordered collection of elements which will not allow duplicates.

Syntax

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.

Maps

Map is key – value pairs.

Syntax

map<datatype,datatype> mapName = new map<datatype,datatype>();

• First datatype is key and it allows primitive datatypes and should be unique.
• Second datatype is values and it allows both primitive & non-primitive datatypes and allows duplicates.

 

Methods in List

Add

Add the values to the list.

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

colors.add(‘Red’);

colors.add(‘White’);

colors.add(‘Black’);    (OR)   

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

Get

Retrieve a values from list using index.

String getcolor = colors.get(1); —-  we get the value is ‘White’ in to getcolor veriable.

Set

Replaces a former value with the value at given index.

colors.set(1,’Green’); —-   List has value at index ‘ 1 ‘ is White is changed to Green.

Size

Return the number of elements in the list.

colors.size(); —-    Gives the size of colors list is ‘2’

Clear

Remove the elements from the list.

colors.clear();

 

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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 ;

}

}

Write in Anonymous block and excute it.

list<contact> contactList = new list<contact>();

for(integer i=0; i<100 ; i++ ){

contact cont = new contact(lastname = 'prasadl' + i);

    system.debug('names are : '+'prasadl'+i);

contactList .add(cont);

}

insert contactList ;

 Set Methods

set<string> myString = new Set<String>{'a', 'b'};

    myString.add('d');

system.debug('add method = ' +myString);

   mystring.remove('a');

system.debug('remove method = ' +mystring);

system.debug('contains method = ' +myString.contains('c'));

system.debug('isempty method = ' +mystring.isempty());

  set<string> myString1 = myString.clone();

system.debug('clone method = ' +mystring1);

Methods

Put()

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

•    map.put(key,value);

Get()

Retrieves the value for a key.

• map.get(key);

keySet()

Retrieves all the keys and return type is set;

• map.keySet();

values()

Retrieves all the values and return type is list;

• map.values();

Size()

Return the number of components in the map.

• map.size();

Example: 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.id,acc1);

accountIdMap .put(acc2.id,acc2);

accountIdMap .put(acc3.id,acc3);

}

}

Ex:

List<Account> ls = [select Id,Name from Account];

Map<Id, Account> m = new Map<Id, Account>(ls);

       Insert new record to the map

account a = new account(name = 'basha');

m.put(a.id,a);

insert a;

system.debug('new record '+a);

       Get Record From map

account name1 = m.get('0019000000yVODTAA4');

system.debug('specific value' +name1);

       Print Ids in the map

system.debug('map ids ' +m.keyset());

       print values in the map

system.debug('map ids and values' +m.values());

       copy one map to another map

Map<Id, Account> m1 = new Map<Id, Account>(m);

system.debug('map ids and values' +m1.values());

       Size of the map

system.debug('map elements size' +m.size());

       Map is empty or not

system.debug('map is empty or not' +m.isempty());

       Clear the map

m1.clear();

system.debug('map ids and values' +m1);

Map<Integer, Account> M = new Map<Integer, Account>();

       Verify if the list of sObjectscontains Account tokens

system.debug('=======map=====' +M.getSObjectType());

System.assertEquals( M.getSObjectType(), Account.sObjectType);