Professional BlazeDS: Creating Rich Internet Applications with Flex® and Java®

A.1. What Is Flex 4?

Flex 4 (codenamed "Gumbo"), like its earlier versions, is an ActionScript 3 (AS3) framework for application development. It includes a set of ready-to-use components and layout containers and provides service components to access external data. For rapid and intuitive development, the framework includes an XML-based declarative markup language called MXML, which can be used to write a lot, if not all, of a Flex application. The framework code bundled with a compiler and a set of utilities is distributed as a software development kit (SDK). Besides, Adobe offers an Eclipse-based IDE for Flex application development. The IDE is branded as Flex Builder. In this book, I focus on the SDK and leave the IDE out of discussion.

Flex applications, on compilation, become byte code that can be understood by the ActionScript Virtual Machine (AVM) of a Flash Player. The byte code files are commonly referred to as SWF (pronounced "swiff") files. These files derive this name from "Shockwave Flash" and include ".swf" as extension to their filenames. Flex 4 exclusively targets Flash Player 10 and the AVM 2 virtual machine.

Let's start by exploring what's new in Flex 4.

A.1.1. What's New?

In order to understand the new features in Flex 4, you need to know what exists in the current versions of Flex. Chapter 1 introduces Flex 3, and you will benefit from reading it again to refresh your memory about the concepts.

The modifications and additions to Flex are inspired by an underlying ...