Salesforce apex list class and methods with practice examples

List is one of the collections in apex. A list is an ordered collection of elements, where each element can be accessed by its index. Apex lists class provides a number of methods to handle groups of records in salesforce.

In this guide, we will dive into list manipulation in salesforce apex, explaining essential list methods to use for real-world business scenarios.

Key topics

How to Create a List in Apex
What are the list methods
Exception - List has no rows for assignment to SObject
Exception - List index out of bounds
Apex list practice examples

How to Create a List

To create a list, use the List keyword followed by angle brackets containing the data type.

Here is an example :

List<String> fruitList = new List<String>();

Note : Lists must always be initialized. If you operate on an uninitialized list, you may cause a null pointer exception.

What are the list methods

Salesforce apex list class provides a rich set of methods to manipulate lists. These methods allow developers to perform a variety of operations, such as adding, removing, sorting, and searching elements within a list.

The following are some of the most important list class methods available in Salesforce.

1. add

This method adds an element to the end of the list.

List<String> names = new List<String>{'Alice', 'Bob'};
names.add('Charlie');
System.debug('Names: ' + names); //Names: (Alice, Bob, Charlie)

2. addAll

This method adds all the elements from another list to the end of the current list.

List<String> names = new List<String>{'Alice', 'Bob'};
List<String> moreNames = new List<String>{'David', 'Eve'};
names.addAll(moreNames);
System.debug('Names after addAll: ' + names); //Names after addAll: (Alice, Bob, David, Eve)

3. clear

This method removes all elements from the list.

List<Integer> numbers = new List<Integer>{1, 2, 3, 4, 5};
numbers.clear();
System.debug('List after clear(): ' + numbers); // List after clear(): ()

4. contains

This method returns true if the list contains the specified element, otherwise it returns false.

List<String> fruits = new List<String>{'Apple', 'Banana'}; 
Boolean containsBanana = fruits.contains('Banana');
System.debug('Contains Banana: ' + containsBanana ); //Contains Banana: true

5. get

This method returns the element at the specified index in the list.

List<String> fruits = new List<String>{'Apple', 'Banana'}; 
 String secondFruit = fruits.get(1);
System.debug('The fruit at index 1 is: ' + secondFruit); //The fruit at index 1 is: Banana

6. indexof

This method returns the index of the first occurrence of the specified element in the list, or-1 if the element is not found.

List<String> fruits = new List<String>{'Apple', 'Banana', 'Cherry'};
Integer missingIndex = fruits.indexOf('Grape');
System.debug('The index of Grape is: ' + missingIndex); //The index of Grape is: -1

7. isEmpty

This method returns true if the list is empty,otherwise it returns false.

List<Integer> numbers = new List<Integer>();
Boolean isListEmpty = numbers.isEmpty();
System.debug('Is the list empty? ' + isListEmpty); // Is the list empty? true

8. remove

This method removes the first occurrence of the specified element from the list.

List<Integer> numbers = new List<Integer>{10, 20, 30, 40, 50};
Integer removedElement = numbers.remove(2); 
System.debug('List after removing by index: ' + numbers); //List after removing by index: (10, 20, 40, 50)

9. set

This method replaces the element at the specified index in the list with the specified element.

List<String> fruits = new List<String>{'Apple', 'Banana', 'Cherry', 'Date'};
fruits.set(1, 'Blueberry');
System.debug('List after use set(): ' + fruits); // List after use set(): (Apple, Blueberry, Cherry, Date)

10. size

This method returns the number of elements in the list.

List<String> fruits = new List<String>{'Apple', 'Banana', 'Cherry', 'Date'};
Integer listSize = fruits.size();
System.debug('The size of the list is: ' + listSize); //The size of the list is: 4

11. sort

This method sorts the elements in the list in ascending order, based on their natural ordering.

List<Integer> numbers = new List<Integer>{5, 3, 9, 1};
numbers.sort();
System.debug('Sorted numbers: ' + numbers); //Sorted numbers: (1, 3, 5, 9)

Exception - List has no rows for assignment to SObject

This exception happens when you try to use a value from a list that was created using a SOQL query, but the list is empty.

For example:

Account accRecord = [Select name from Account where Type = 'Prospect' ];
String accountName = accRecord.name;

The select query always returns a list. Always check if the list is empty before accessing the values from the list.

The modified code for the above scenario is :

List<Account> accRecords = [Select name from Account where Type = 'Prospect' ];

if(accRecords.size()>0){
    String accountName = accRecord[0].name;
}

Exception - List index out of bounds

Apex throws a "List index out of bounds" exception when you try to access an element in a list using an index that doesn't exist in the list. Here is an example:

 List<Integer> numbers = new List<Integer>{1, 2, 3};
//Throws List index out of bounds
Integer invalidNumber = numbers[4]; // Tries to access the 5th element (index 4), but the list only has 3 elements

To avoid this happening in your code, always check the list size before accessing an index.

Apex list practice examples

Following are a list of practice examples to learn and use the apex list methods. Click the following links to see the apex practice problems.