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The collection is the type of variables that can store multiple numbers of records. It can increase and decrease dynamically.
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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add(listElement) Example:
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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);
}
}
}
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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();
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 ():
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>
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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