What is List Class in Salesforce?

Hi,

List method is used for all instance methods. This operates on any particular instance of list.
For example:-
MyFirstList.clear();

In the above example, I am clearing all element of the MyFirstList instance.

Below is the list of all related constructors and method of the List Class:-

Constructor

• List()
  Creates a new instance of the List class. A list can hold elements of any data type T.
• List(listToCopy)
  Creates a new instance of the List class by copying the elements from the specified list. T is the data type of the elements in both lists and can be any data type.
• List(setToCopy)
  Creates a new instance of the List class by copying the elements from the specified set. T is the data type of the elements in the set and list and can be any data type.

Method

• add(listElement)
  Adds an element to the end of the list.
• add(index, listElement)
  Inserts an element into the list at the specified index position.
• addAll(fromList)
  Adds all of the elements in the specified list to the list that calls the method. Both lists must be of the same type.
• addAll(fromSet)
  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.
• clear()
  Removes all elements from a list, consequently setting the list's length to zero.
• clone()
  Makes a duplicate copy of a list.
• contains(listElement)
  Returns true if the list contains the specified element.
• deepClone(preserveId, preserveReadonlyTimestamps, preserveAutonumber)
  Makes a duplicate copy of a list of sObject records, including the sObject records themselves.
• equals(list2)
  Compares this list with the specified list and returns true if both lists are equal; otherwise, returns false.
• get(index)
  Returns the list element stored at the specified index.
• getSObjectType()
  Returns the token of the sObject type that makes up a list of sObjects.
• hashCode()
  Returns the hashcode corresponding to this list and its contents.
• indexOf(listElement)
  Returns the index of the first occurrence of the specified element in this list. If this list does not contain the element, returns -1.
• isEmpty()
  Returns true if the list has zero elements.
• iterator()
  Returns an instance of an iterator for this list.
• remove(index)
  Removes the list element stored at the specified index, returning the element that was removed.
• set(index, listElement)
  Sets the specified value for the element at the given index.
• size()
  Returns the number of elements in the list.
• sort()
  Sorts the items in the list in ascending order.

Hope this will help you to understand List Class.

Thanks!

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.

Lists can contain any collection and can be nested within one another and become multidimensional. For example, you can have a list of lists of sets of Integers. A list can contain up to four levels of nested collections inside it, that is, a total of five levels overall.

To declare a list, use the List keyword followed by the primitive data, sObject, nested list, map, or set type within <> characters.

Ex:

// Create an empty list of String
List<String> my_list = new List<String>();
// Create a nested list
List<List<Set<Integer>>> my_list_2 = new List<List<Set<Integer>>>();

Thanks