Loops – FOR and FOREACH loops

Preface – This post is part of the Core Apex Tools series.

Every trigger in Salesforce will have a loop! These are very important to learn!

Loops are a popular coding tool that let you repeatedly execute code.

A FOREACH loop is the most popular type of loop in Apex. FOREACH loops let you repeatedly execute code on every element of a list:

List<Contact> allContacts = [SELECT Id FROM Contact];
for (Contact currentContact : allContacts) {
    // This is my contact ID. People love me!
    currentContact.Best_Friend__c = '003i000000Mnm1R';
}

Remember, the green highlighted code is the most important – here it represents the loop. Everything inside is the code that executes for each Contact in our list. There are two important variables in this loop: currentContact and allContacts.

currentContact is the variable we designate to represent the current Contact in each iteration of the loop. If we’re iterating over 200 contacts, currentContact will separately represent each contact, one-by-one, until all 200 have gone through the loop. We preface this variable with Contact to let Salesforce know what kind of object it is.

allContacts is the List the loop will iterate over. Each Contact in this list will run through the code inside the brackets { } exactly once!

A traditional FOR loop lets you repeatedly execute code a specific number of times:

for (Integer i = 0; i < 5; i++) {
    // Create five new imaginary friends!
    Contact friend = new Contact();
    friend.FirstName = 'Kate';
    friend.LastName  = 'Upton #' + i;
    friend.Best_Friend__c = '003i000000Mnm1R';
    insert friend;
}

The traditional FOR loop is a little different because instead of iterating over a list, you’re iterating over a defined number of iterations.

In the very first line this reads:
  1. For a new integer we define as “i” that starts at zero
  2. Iterate while “i” is less than 5
  3. After each iteration, increment “i” by one

Notice how we use the integer “i” inside the loop! Five Kate Uptons will be created with the exact names: “Kate Upton #0”, “Kate Upton #1”, “Kate Upton #2″…

Now what am I going to do with five Kate Uptons all to myself?

Salesforce coding party!!

Next post: Comparison operators!