Salesforce Apex List Class Guide

Introduction

A list is a collection that allows you to store multiple values of the same data type in a specific order. The Salesforce Apex List class provides methods to work with lists efficiently.

Key features and characteristics of Salesforce Apex lists include:

• Homogeneous Elements: A list in Apex can store elements of the same data type. For example, a list can hold a collection of strings, integers, custom objects, or any other data type.
• Dynamic Size: Lists in Apex are dynamic, meaning they can grow or shrink as elements are added or removed. You don’t need to specify the initial size of the list.
• Ordered Collection: Elements in a list maintain their order based on the index position. The first element has an index of 0, the second element has an index of 1, and so on.
• Zero-Based Indexing: Apex list elements are accessed using a zero-based index. This means that the first element is at index 0, the second element is at index 1, and so on.
• Methods and Operations: The Apex List class provides various methods and operations to manipulate and work with lists. These include adding elements, removing elements, accessing elements by index, sorting, searching, and more.
• Iteration: Lists can be iterated using loops or iterators, allowing you to process each element sequentially.

Salesforce Apex lists are commonly used to store and manage collections of data, such as records retrieved from a database, query results, or any set of related values. They offer flexibility, ease of use, and powerful operations for working with collections of data in the Salesforce platform.

Apex list methods

Let’s take a look at the methods the Apex List Class provides.

add

The List Class provides two add methods to add elements to a list.

To add an element by appending it to the list at the end use the following variant of the add list.

List<String> fruits = new List<String>();
fruits.add('apple');
System.assertEquals('apple', fruits.get(0));

To add an element at a postion of your choice, you need to provide the position and the element to the add method.

List<String> fruits = new String[4];
fruits.add(3,'apple');
System.assertEquals('apple', fruits.get(3));

addAll

To merge to lists, you can call the addAll method an list and pass a another list to it. This way the list gets the added elements appended at the end.

List<String> fruits = new List<String>();
fruits.add('apple');

List<String> moreFruits = new List<String>();
moreFruits.add('orange');

fruits.addAll(moreFruits);

System.assertEquals('orange', fruits.get(1));

To add a set, you can also call the addAll method.

List<String> fruits = new List<String>();
fruits.add('apple');

Set<String> moreFruits = new Set<String>();
moreFruits.add('orange');

fruits.addAll(moreFruits);

System.assertEquals('orange', fruits.get(1));

clear

To remove all elements of a list call the clear method.

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

fruits.add('apple');
System.assertEquals(1, fruits.size());

fruits.clear();
System.assertEquals(0, fruits.size());

contains

In case you need a to know, whether an element is within a list or not, use the contains method.

List<String> fruits = new List<String>();
System.assertEquals(false, fruits.contains('apple'));
fruits.add('apple');
System.assertEquals(true, fruits.contains('apple'));

get

To get an element of a list at concrete position, use the get method and pass the position to the method.

List<String> fruits = new List<String>();
try {
    System.assertEquals(null, fruits.get(0));
    System.Assert.fail();
} catch (System.ListException e) {
}
fruits.add('apple');
System.assertEquals('apple', fruits.get(0));

indexOf

To find out, at which index an element is within a list, use the indexOf method.

List<String> fruits = new List<String>();
fruits.add('apple');
fruits.add('orange');
System.assertEquals(1, fruits.indexOf('orange'));
System.assertEquals(-1, fruits.indexOf('melon'));

isEmpty

To check if a list is empty or not, use the isEmpty method.

List<String> fruits = new List<String>();
System.assertEquals(true, fruits.isEmpty());
fruits.add('apple');
System.assertEquals(false, fruits.isEmpty());

iterator

To iterate over a list, you can use the iterator you retrieve by the iterator method.

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

fruits.add('apple');

Iterator<String> it =  fruits.iterator();
while(it.hasNext()){
    System.debug('iterate');
    System.assertEquals('apple',it.next());
}

remove

To remove an element of a list, use the remove method.

List<String> fruits = new List<String>();
fruits.add('apple');
System.assertEquals('apple',fruits.remove(0));
try {
    fruits.remove(1);
    System.Assert.fail();
}catch (System.ListException e){
}

set

To set the element of list at a concrete position, use the set method.

List<String> fruits = new List<String>();
System.assertEquals(0,fruits.size());
fruits.add('apple');
fruits.set(0,'orange');
System.assertEquals('orange', fruits.get(0));

size

To find out the size of a list, use the size method.

List<String> fruits = new List<String>();
System.assertEquals(0,fruits.size());
fruits.add('apple');
System.assertEquals(1, fruits.size());

sort

To sort the elements of a list, use the sort method.

List<String> fruits = new List<String>();
fruits.add('orange');
fruits.add('apple');
fruits.add('melon');

System.assertEquals('orange',fruits.get(0));
System.assertEquals('apple',fruits.get(1));
System.assertEquals('melon',fruits.get(2));

fruits.sort();

System.assertEquals('apple',fruits.get(0));
System.assertEquals('melon',fruits.get(1));
System.assertEquals('orange',fruits.get(2));