Note: This release is in preview. Features described here don’t become generally available until the latest general availability date that Salesforce announces for this release. Before then, and where features are noted as beta, pilot, or developer preview, we can’t guarantee general availability within any particular time frame or at all. Make your purchase decisions only on the basis of generally available products and features.

Assignment Statements

An assignment statement is any statement that places a value into a variable.

An assignment statement generally takes one of two forms:

1[LValue] = [new_value_expression];
2[LValue] = [[inline_soql_query]];

In the forms above, [LValue] stands for any expression that can be placed on the left side of an assignment operator. These include:

A simple variable. For example:

1Integer i = 1;
2Account a = new Account();
3Account[] accts = [SELECT Id FROM Account];

A de-referenced list element. For example:
1ints[0] = 1; 2accts[0].Name = 'Acme';

An sObject field reference that the context user has permission to edit. For example:

1Account a = new Account(Name = 'Acme', BillingCity = 'San Francisco'); 
2
3// IDs cannot be set prior to an insert call
4// a.Id = '00300000003T2PGAA0';   
5
6// Instead, insert the record. The system automatically assigns it an ID.
7insert a;
8
9// Fields also must be writable for the context user
10// a.CreatedDate = System.today();  This code is invalid because
11//                                  createdDate is read-only! 
12
13// Since the account a has been inserted, it is now possible to
14// create a new contact that is related to it
15Contact c = new Contact(LastName = 'Roth', Account = a);
16
17// Notice that you can write to the account name directly through the contact 
18c.Account.Name = 'salesforce.com';

Assignment is always done by reference. For example:

1Account a = new Account();
2Account b;
3Account[] c = new Account[]{};
4a.Name = 'Acme';
5b = a;         
6c.add(a);      
7
8// These asserts should now be true. You can reference the data
9// originally allocated to account a through account b and account list c.
10System.assertEquals(b.Name, 'Acme');          
11System.assertEquals(c[0].Name, 'Acme');

Similarly, two lists can point at the same value in memory. For example:

1Account[] a = new Account[]{new Account()};
2Account[] b = a;
3a[0].Name = 'Acme';
4System.assert(b[0].Name == 'Acme');

In addition to =, other valid assignment operators include +=, *=, /=, |=, &=, ++, and --. See Expression Operators.

Apex Developer Guide

Assignment Statements