Apex Developer Guide

Apex Developer Guide
Release Notes
Getting Started with Apex
Writing Apex
Data Types and Variables
Control Flow Statements
Classes, Objects, and Interfaces
Classes
Interfaces
Keywords
Annotations
Classes and Casting
Differences Between Apex Classes and Java Classes
Class Definition Creation
Namespace Prefix
Using the System Namespace
Using the Schema Namespace
Namespace, Class, and Variable Name Precedence
Type Resolution and System Namespace for Types
Apex Code Versions
Lists of Custom Types and Sorting
Using Custom Types in Map Keys and Sets
Working with Data in Apex
Document Your Apex Code
Running Apex
Debugging, Testing, and Deploying Apex
Apex Reference
Appendices
PDF

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.

Using the System Namespace

The System namespace is the default namespace in Apex. This means that you can omit the namespace when creating a new instance of a system class or when calling a system method. For example, because the built-in URL class is in the System namespace, both of these statements to create an instance of the URL class are equivalent:

And:

Similarly, to call a static method on the URL class, you can write either of the following:

Or:

In addition to the System namespace, there is a built-in System class in the System namespace, which provides methods like assertEquals and debug. Don’t get confused by the fact that both the namespace and the class have the same name in this case. The System.debug('debug message'); and System.System.debug('debug message'); statements are equivalent.

Note

Using the System Namespace for Disambiguation

It is easier to not include the System namespace when calling static methods of system classes, but there are situations where you must include the System namespace to differentiate the built-in Apex classes from custom Apex classes with the same name. If your organization contains Apex classes that you’ve defined with the same name as a built-in class, the Apex runtime defaults to your custom class and calls the methods in your class. Let’s take a look at the following example.

Create this custom Apex class:

Execute this statement in the Developer Console:

When the Database.query statement executes, Apex looks up the query method on the custom Database class first. However, the query method in this class doesn’t take any parameters and no match is found, hence you get an error. The custom Database class overrides the built-in Database class in the System namespace. To solve this problem, add the System namespace prefix to the class name to explicitly instruct the Apex runtime to call the query method on the built-in Database class in the System namespace: