Apex Developer Guide

Apex Developer Guide
Getting Started with Apex
Writing Apex
Data Types and Variables
Control Flow Statements
Classes, Objects, and Interfaces
Classes
Apex Class Definition
Class Variables
Class Methods
Using Constructors
Access Modifiers
Static and Instance Methods, Variables, and Initialization Code
Apex Properties
Extending a Class
Extended Class Example
Interfaces
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 Language Reference
Appendices
Glossary
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Extended Class Example

The following is an extended example of a class, showing all the features of Apex classes. The keywords and concepts introduced in the example are explained in more detail throughout this chapter.

This code example illustrates:
  • A top-level class definition (also called an outer class)
  • Static variables and static methods in the top-level class, as well as static initialization code blocks
  • Member variables and methods for the top-level class
  • Classes with no user-defined constructor — these have an implicit, no-argument constructor
  • An interface definition in the top-level class
  • An interface that extends another interface
  • Inner class definitions (one level deep) within a top-level class
  • A class that implements an interface (and, therefore, its associated sub-interface) by implementing public versions of the method signatures
  • An inner class constructor definition and invocation
  • An inner class member variable and a reference to it using the this keyword (with no arguments)
  • An inner class constructor that uses the this keyword (with arguments) to invoke a different constructor
  • Initialization code outside of constructors — both where variables are defined, as well as with anonymous blocks in curly braces ({}). Note that these execute with every construction in the order they appear in the file, as with Java.
  • Class extension and an abstract class
  • Methods that override base class methods (which must be declared virtual)
  • The override keyword for methods that override subclass methods
  • Abstract methods and their implementation by concrete sub-classes
  • The protected access modifier
  • Exceptions as first class objects with members, methods, and constructors

This example shows how the class above can be called by other Apex code:

This code example illustrates:
  • Construction of the outer class
  • Construction of an inner class and the declaration of an inner interface type
  • A variable declared as an interface type can be assigned an instance of a class that implements that interface
  • Casting an interface variable to be a class type that implements that interface (after verifying this using the instanceof operator)