What is the Collection in Salesforce?

Introduction

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.

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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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  From the index number, we can find the Name

Listmylist = new List();
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);
listallName= new list();
allName.addall(mylist);
string name=mylist.get(1);
system.debug(name);.//Philips

Click on Debug resultaddAll(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 firstList = new List();
       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 secondList = new List();
       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);
       }
    }

}





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

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List firstList = new List();
       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 firstList = new List();
       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 CCClear (); This method removes all elements from a list, consequently setting the list size to zero.

List firstList = new List();
       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 firstList = new List();
       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 secondList = new List();
         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 firstList = new List();
       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 secondList = new List();
         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 listStrings = new List {'A', 'B', 'D', 'C'};
 Set setString = new Set {'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 accList {get; set;}
  public List selectedAccounts{get; set;}
  public List getAccounts(){
        if(accList == null){
            accList = new List();
            for(Account acc : [select Id, Name, Phone from Account limit 25]){
                  accList.add(new cAccount(acc));
            }
         }
       return accList;
   }  
  public PageReference processSelected(){    
        selectedAccounts= new List();
        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;
        }
   }

}

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!