Apex Developer Guide

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Apex Developer Guide
Release Notes
Getting Started with Apex
Writing Apex
Data Types and Variables
Control Flow Statements
Conditional (If-Else) Statements
Switch Statements
Loops
Do-While Loops
While Loops
For Loops
Traditional For Loops
List or Set Iteration for Loops
Iterating Collections
Classes, Objects, and Interfaces
Working with Data in Apex
Running Apex
Debugging, Testing, and Deploying Apex
Apex Reference
Appendices
PDF

Iterating Collections

Collections can consist of lists, sets, or maps. Modifying a collection's elements while iterating through that collection is not supported and causes an error. Do not directly add or remove elements while iterating through the collection that includes them.

Adding Elements During Iteration

To add elements while iterating a list, set or map, keep the new elements in a temporary list, set, or map and add them to the original after you finish iterating the collection.

Removing Elements During Iteration

To remove elements while iterating a list, create a new list, then copy the elements you wish to keep. Alternatively, add the elements you wish to remove to a temporary list and remove them after you finish iterating the collection.

The List.remove method performs linearly. Using it to remove elements has time and resource implications.

Note

To remove elements while iterating a map or set, keep the keys you wish to remove in a temporary list, then remove them after you finish iterating the collection.