Apex Developer Guide

Clouds with binary code floating aboveCloud with binary code floating above

No Results

Search Tips:

  • Please consider misspellings
  • Try different search keywords
Apex Developer Guide
Release Notes
Getting Started with Apex
Writing Apex
Data Types and Variables
Control Flow Statements
Classes, Objects, and Interfaces
Classes
Interfaces
Custom Iterators
Keywords
Annotations
Classes and Casting
Differences Between Apex Classes and Java Classes
Class Definition Creation
Namespace Prefix
Apex Code Versions
Lists of Custom Types and Sorting
Using Custom Types in Map Keys and Sets
Working with Data in Apex
Running Apex
Debugging, Testing, and Deploying Apex
Apex Reference
Appendices
PDF

Custom Iterators

An iterator traverses through every item in a collection. For example, in a procedural loop, you define a condition for exiting the loop, and you must provide some means of traversing the collection, that is, an iterator. In this example, count is incremented by 1 every time the loop is executed.
while (count < 11) {
   System.debug(count);
      count++;
   }

Using the Iterator interface you can create a custom set of instructions for traversing a List through a loop. The iterator is useful for data that exists in sources outside of Salesforce that you would normally define the scope of using a SELECT statement. Iterators can also be used if you have multiple SELECT statements.

Using Custom Iterators

To use custom iterators, you must create an Apex class that implements the Iterator interface.

The Iterator interface has the following instance methods:
Name Arguments Returns Description
hasNext Boolean Returns true if there’s another item in the collection being traversed, false otherwise.
next Any type Returns the next item in the collection.

All methods in the Iterator interface must be declared as global or public.

This example code uses a custom iterator to iterate through a list of strings.
IterableString x = new IterableString('This is a really cool test.');

while(x.hasNext()){
   system.debug(x.next());
}

Using Custom Iterators with Iterable

If you don’t want to use a custom iterator with a list, but instead want to create your own data structure, you can use the Iterable interface to generate the data structure.

The Iterable interface has the following method:
Name Arguments Returns Description
iterator Iterator class Returns a reference to the iterator for this interface.

The iterator method must be declared as global or public. It creates a reference to the iterator that you can then use to traverse the data structure.

In the following example a custom iterator iterates through a collection: 
public class CustomIterator
   implements Iterator<Account>{ 
 
   private List<Account> accounts;
   private Integer currentIndex;
 
   public CustomIterator(List<Account> accounts){
       this.accounts = accounts;
       this.currentIndex = 0;
   }
 
   public Boolean hasNext(){ 
       return currentIndex < accounts.size();
   }    
 
   public Account next(){
       if(hasNext()) {
           return accounts[currentIndex++];
       } else {
           throw new NoSuchElementException('Iterator has no more elements.');
       }
   } 
}
public class CustomIterable implements Iterable<Account> {
   public Iterator<Account> iterator(){
      List<Account> accounts =
      [SELECT Id, Name,
       NumberOfEmployees 
       FROM Account
       LIMIT 10];
      return new CustomIterator(accounts);
   }
}
The following is a batch job that uses an iterator:
public class BatchClass implements Database.Batchable<Account>{
   public Iterable<Account> start(Database.BatchableContext info){
       return new CustomIterable();
   }
   public void execute(Database.BatchableContext info, List<Account> scope){
       List<Account> accsToUpdate = new List<Account>();
       for(Account acc : scope){
           acc.Name = 'changed';
           acc.NumberOfEmployees = 69;
           accsToUpdate.add(acc);
       }
       update accsToUpdate;
   }
   public void finish(Database.BatchableContext info){
   }
}