What is the Collection in Salesforce? (2020 updated)

What is the Collection in Salesforce?

The collection is the type of variables that can store multiple numbers of records. It can increase and decrease dynamically.

There are 3 types of collection

1. List Collection
2. Set Collection
3. Map Collection

List Collection

It creates a new instance of the List class. A list can hold elements of any data type. A list is an interface. A list is an ordered collection of typed primitives, sObjects, user-defined objects, Apex objects or collections that are distinguished by their indices. A list is an ordered collection so use list when you want to identify the list element based on Index Number. The list can contain Duplicates. A list should be declared with “List” keyword. To define a list use list keyword by primitive data, sObject within <> characters. The index position of the first element in a list always starts with [0].it can grow dynamically at the run. It allows duplicate and null values.

Methods in list

There are few methods available in the list

• add(list Element)
• add(index, list Element)
• addAll(from List)
• addAll(from Set)
• clear()
• clone()
• Remove()
• Size()
• equals(list2)

add(listElement) Example:

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Index 0 Index 1 Index 2 Index 3 Index 4

Daniel Philips Josh Michel Samuel

  From the index number, we can find the Name

List<String>mylist = new List<String>();
string n1= ‘Daniel’;
string n2= ‘Philips’;
string n3= ‘Josh’;
string n4=’ Michel’;
string n5=’ Samuel’;
mylist.add(n1);
mylist.add(n2);
mylist.add(n3);
mylist.add(n4);
mylist.add(n5);
list<string>allName= new list<string>();
allName.addall(mylist);
string name=mylist.get(1);
system.debug(name);.//Philips

Click on Debug result addAll(from List): Addall of the elements in the specified list to the list that calls the method. Both lists must be of the same type.

public class ExampleOfList {
      public static void addAlltest() {
       List<String> firstList = new List<String>();
       firstList.add('Justin');
       firstList.add('FRANK');
       firstList.add('LOUIS');
       for(string name1:firstList){
      System.debug('First List Details is-->'+ ''+name1);
   }
     system.debug('First List size is-->'+ firstList.size());
       List<String> secondList = new List<String>();
       secondList.add('ALBERT');
       secondList.add('JACKSON');
       secondList.add('FREDDIE');
       secondList.addAll(firstList);
          system.debug('Both list names are '+' '+secondList+''+secondList.size());
          for(String name : secondList){
           System.debug('Second List Details is-->'+ ''+name);
       }
    }

}

Debug result Remove ():  It removes the list element stored at specific index, returning the element that was removed 

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List<String> firstList = new List<String>();
       firstList.add('FREDDIE');
       firstList.add('JACKSON');
       firstList.add('ALBERT');
       firstList.remove(2); //remove 2nd position value.
       for(String name : firstList){
           System.debug(name);
       }
    }
Debug result //ALBERT removed from list

Sort();

This method s sorts list in ascending order.

List<String> firstList = new List<String>();
       firstList.add('Justin');
       firstList.add('FRANK');
       firstList.add('LOUIS');
       firstList.add('ALBERT');
       firstList.add('JACKSON');
       firstList.add('FREDDIE');
       for(string name1:firstList){
      System.debug('First List Details is-->'+ ''+name1);
   }
         firstList.sort();
          system.debug('Names are in alphabate from '+' '+firstList);

Debug result CC Clear (); This method removes all elements from a list, consequently setting the list size to zero.

List<String> firstList = new List<String>();
       firstList.add('Justin');
       firstList.add('FRANK');
       firstList.add('LOUIS');
       firstList.add('ALBERT');
       firstList.add('JACKSON');
       firstList.add('FREDDIE');
       for(string name1:firstList){
           System.debug('First List Details is-->'+ ''+name1);
   }
         firstList.clear();
          system.debug('list size is '+' '+firstList);

Clone ():

This method will make a duplicate copy of list

List<String> firstList = new List<String>();
       firstList.add('Justin');
       firstList.add('FRANK');
       firstList.add('LOUIS');
       firstList.add('ALBERT');
       firstList.add('JACKSON');
       firstList.add('FREDDIE');
       for(string name1:firstList){
           System.debug('First List Details is-->'+ ''+name1);
   }
      List<String> secondList = new List<String>();
         secondList=firstList.clone();
        system.debug(secondList);

Equals(List); Compares the list with the specific list and returns true if both are equals, otherwise, returns false.

List<String> firstList = new List<String>();
       firstList.add('Justin');
       firstList.add('FRANK');
       firstList.add('LOUIS');
       firstList.add('ALBERT');
       firstList.add('JACKSON');
       firstList.add('FREDDIE');
       for(string name1:firstList){
           System.debug('First List Details is-->'+ ''+name1);
   }
      List<String> secondList = new List<String>();
         secondList.add('Justin');  
         secondList.add('FRANK');
         secondList.add('ALBERT');
        Boolean result;
       result=secondList.equals(firstList);
       system.debug(result);

addAll(Set) : Add all of the elements in specified set to the list that calls the method. The set and the list must be of the same type.

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List<String> listStrings = new List<String> {'A', 'B', 'D', 'C'};
 Set<String> setString = new Set<String> {'F', 'V', 'Z'};
 listStrings.addAll(setString);
system.debug(listStrings);
Debug output is |DEBUG| (A, B, D, C, F, V, Z)

Example How to display selected record in another section using list Apex class

public class listDemoEx {
  public List<cAccount> accList {get; set;}
  public List<Account> selectedAccounts{get; set;}
  public List<cAccount> getAccounts(){
        if(accList == null){
            accList = new List<cAccount>();
            for(Account acc : [select Id, Name, Phone from Account limit 25]){
                  accList.add(new cAccount(acc));
            }
         }
       return accList;
   }  
  public PageReference processSelected(){    
        selectedAccounts= new List<Account>();
        for(cAccount cCon : getAccounts()) {
            if(cCon.selected == true){
                selectedAccounts.add(cCon.con);
            }
        }           
        return null;
   }

  public class cAccount {
        public Account con {get; set;}
        public Boolean selected {get; set;}
        public cAccount(Account c) {
            con = c;
            selected = false;
        }
   }

}

Visualforce Page

<apex:page controller="listDemoEx" sidebar="true" showHeader="true">
<apex:form >
<apex:pageBlock title="ACCOUNT">
<apex:pageBlockButtons >
<apex:commandButton value="Selected Item" action="{!processSelected}" rerender="out"/>
</apex:pageBlockButtons>
<apex:pageBlockSection columns="2">
<apex:pageBlockTable value="{!Accounts}" var="Acc" columnsWidth="150px,150px" align="left">
<apex:column >
<apex:inputCheckbox value="{!Acc.selected}"/>
</apex:column>
<apex:column value="{!Acc.con.Name}" />
<apex:column value="{!Acc.con.Phone}" />
</apex:pageBlockTable>
<apex:pageBlockTable value="{!selectedAccounts}" var="Rec" id="out" align="right" title="Selected Accounts">
<apex:column headerValue="Account Name">
<apex:outputField value="{!Rec.name}"/>
</apex:column>
<apex:column headerValue="Phone">
<apex:outputField value="{!Rec.Phone}"/>
</apex:column>
</apex:pageBlockTable>
</apex:pageBlockSection>
</apex:pageBlock>
</apex:form>
</apex:page>

Summary

Apex is an intelligent programming platform for Salesforce. You can have a real fun with it by utilizing Collections. Share your creativity with us using the comment section below. Happy coding!

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