Lists in APEX

Chapter Topics

A list in Apex is an ordered collection of elements used to store data in sequence. These elements can be any data type—primitive types, collections, sObjects, user-defined types, and built-in Apex types.

Let’s understand Lists in Apex with examples

Suppose there is a list (‘Violet’, ‘Indigo’, ‘Blue’, ‘Yellow’, ‘Red’, ‘Purple’).

The index and value of each element will be as follows:

Violet	Indigo	Blue	Yellow	Red	Purple
0th	1st	2nd	3rd	4th	5th

Why do We Use Lists in Salesforce?

Lists in Salesforce, specifically in Apex, are used for several important reasons:

Dynamic Size: Lists can grow or shrink, allowing you to store an unknown number of elements without predefining their size.
Data Management: They help in managing collections of data, such as SObject records or custom data types, efficiently. This is particularly useful when handling bulk data operations.
Iteration and Access: Lists allow easy iteration and element access via indexes. This makes it simple to loop through collections of records or other data structures.
Flexibility: You can add, remove, and manipulate elements within lists easily. This flexibility is beneficial when developing complex business logic and algorithms.
Integration with Salesforce Features: Lists integrate seamlessly with many Salesforce features. For instance, when querying records with SOQL (Salesforce Object Query Language), the results are often stored in lists.
Support for Complex Data Structures: Lists can be used to create complex data structures, such as lists of lists, maps of lists, and so on, providing powerful ways to structure and process data.

Properties Of Lists In Apex

There are 2 main properties of lists:

It stores data in sequential order.
The data that it stores is non-unique or can be duplicated.

Hence, use a list when the sequence of elements is important and when the uniqueness of the elements is not.

How to Create a List of Lists in Apex?

Creating a list of lists in Salesforce Apex is straightforward. Here’s a step-by-step guide to help you understand the process:

Define a List: Start by defining a list. In Apex, lists are dynamic arrays that can hold collections of objects.
Create a List of Lists: You can create a list of lists by defining a list whose elements are also lists.

For example:

// Create individual lists
List<String> firstList = new List<String>{'A', 'B', 'C'};
List<String> secondList = new List<String>{'D', 'E', 'F'};
List<String> thirdList = new List<String>{'G', 'H', 'I'};

// Create a list of lists
List<List<String>> listOfLists = new List<List<String>>();

// Add individual lists to the list of lists
listOfLists.add(firstList);
listOfLists.add(secondList);
listOfLists.add(thirdList);

// Accessing elements from the list of lists
System.debug(listOfLists[0][1]); // Output: B
System.debug(listOfLists[1][2]); // Output: F
System.debug(listOfLists[2][0]); // Output: G
                    

List Methods in Apex

The following are methods for List. All are instance methods.

S.No	Function	Example
1	`add(listElement) Adds an element to the end of the list.`	`List myList = new List(); myList.add(47);`
2	`add(index, listElement) Inserts an element into the list at the specified index position.`	`List myList = new List(); myList.add(0, 47); myList.add(1, 52);`
3	`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.`	`List myList1 = new List{1, 2}; List myList2 = new List{3, 4}; myList1.addAll(myList2);`
4	`addAll(fromSet) Adds all of the elements in the specified set to the list that calls the method. The set and the list must be of the same type.`	`List myList = new List{1, 2}; Set mySet = new Set{4, 5}; myList.addAll(mySet);`
5	`clear() removes all elements from a list, setting its length to 0.`	`List myList = new List{1, 2}; myList.clear();`
6	`clone() Makes a duplicate copy of a list.`	`List myList1 = new List{'a', 'b'}; List myList2 = myList1.clone();`
7	`contains(listElement) Returns true if the list contains the specified element.`	`List myList = new List{'a', 'b'}; Boolean result = myList.contains('z');`
8	`deepClone(preserveId, preserveReadonlyTimestamps, preserveAutonumber) Makes a duplicate copy of a list of sObject records, including the sObject records themselves.`	`Account a = new Account(Name='Acme', BillingCity='New York'); Account b = new Account(Name='Salesforce'); List q1 = new List{a, b}; List q2 = q1.deepClone();`
9	`equals(list2) Compares this list with the specified list and returns true if both lists are equal; otherwise, returns false.`	`List myList1 = new List{'a', 'b'}; List myList2 = new List{'a', 'd'}; Boolean result = myList2.equals(myList1);`
10	`get(index) Returns the list element stored at the specified index.`	`List myList1 = new List{'a', 'b'}; String result = myList1.get(1);`
11	`getSObjectType() Returns the token of the sObject type that makes up a list of sObjects.`	`SObject sObj = [SELECT Id FROM Account LIMIT 1]; System.debug(sObj.getSObjectType());`
12	`hashCode() Returns the hashcode corresponding to this list and its contents.`	`List myList1 = new List{'a', 'b'}; System.debug(myList1.hashCode());`
13	`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.`	`List myList1 = new List{'a', 'b', 'a'}; Integer result = myList1.indexOf('a');`
14	`isEmpty() Returns true if the list has zero elements.`	`List myList = new List{'a', 'b'}; Boolean result = myList.isEmpty();`
15	`iterator() Returns an instance of an iterator for this list.`	`List fruit = new List{'Orange', 'Apple', 'Banana', 'Peach'}; Iterator fruitIterator = fruit.iterator();`
16	`remove(index) Removes the list element stored at the specified index, returning the element that was removed.`	`List colors = new List{'Red', 'Blue', 'Green'}; colors.remove(2);`
17	`set(index, listElement) Sets the specified value for the element at the given index.`	`List colors = new List{'Red', 'Blue', 'Green'}; colors.set(2, 'Yellow');`
18	`size() Returns the number of elements in the list.`	`List colors = new List{'Red', 'Blue', 'Green'}; Integer size = colors.size();`
19	`sort() Sorts the items in the list in ascending order.`	`List myList1 = new List{'a', 'e', 'c', 'b'}; myList1.sort();`
20	`toString() Returns the string representation of the list.`	`List myList1 = new List{1, 2, 3, 4}; String myList2 = myList1.toString();`

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Frequently Asked Questions

What are the properties of List in Apex?

The two properties of List in Apex are: 1. They store data in sequential order. 2. They allow duplicacy or non-unique values.

What are List methods in Apex?

There are multiplelist methods in Apex such as, contains(), sort(), isEmpty(), indexOf(), equals(), add(), remove(), get(), and more.

When should you use List in Apex?

In Apex, a list should be used to store an ordered collection of elements that allows duplicates, and you want to navigate records in sequence.

How to loop through a list in Apex?

To loop through a list in Apex, use a “for” loop or an enhanced “for-each” loop.