Java

Even though the Java programming language became popular largely because of applets and the famous dancing Duke (http://java.com/en/download/help/testvm.xml ), applets haven't become Java's main use pattern. The main reason: the large footprint of the required JVM (currently 16MB). And there are other drawbacks. For instance, although Java Swing pushed a platform-independent look-and-feel, absent any good-looking off-the-shelf GUI widgets it was hard selling it to the public. In this regard Flash and Flex creators did a much better job with their eye-candy components. Or take audio and video integration. Today people are used to having streaming audio and video components embedded in Web pages. But the multimedia Java API remains rudimentary, to say the least.
There are some efforts to minimize the size of the JVM used by Web browsers and the Java Browser Edition project now needs "only" about 3MB to run a primitive Hello World applet. But this can't compete with Flash Player 9, which managed to accommodate two virtual machines in a 1.2MB download that can run any RIA however complex.
Another issue with Java applets is that they don't offer a seamless download of the proper version of the JVM along with the applet. Flash Player's express install does precisely that.
Having said that, I must acknowledge that Java Swing is a very mature and robust technology for creating GUI applications delivered either over the Web or installed on the desktop. You can do literally anything with Java Swing - if you can afford it. No, you don't pay licensing fees, but because of the longer development cycle and need to engage expert programmers, industrial-size Swing projects are usually quite expensive to build and maintain.

Adobe Flex 2

Flex 2 applications run cross-platform in a ubiquitous Flash Player 9 that's a lightweight virtual machine. The platform includes:

• an XML-based language called MXML that supports the declarative programming of GUI components targeting designers;
• the standard object-oriented programming language, ActionScript 3.0, based on the latest ECMAScript specification;
• server-side integration via Flex Data Services giving client applications transparent access to the world of J2EE;
• charting components, access to multimedia controls, etc;
• and an Eclipse-based full-featured IDE with automated deployment, debugging, and tracing facilities.

The Flex 2 platform is easily extendable and integrates well with server-side Java, ColdFusion, PHP, Ruby, ASP, and the like.
The SWF file format is open, and there are third-party open source products that offer tools for creating RIAs delivered by Flash Player like OpenLaszlo from Laszlo Systems.
This is what comes at no cost with Flex 2:

• MXML - an XML-based declarative programming language for creating GUI.
• ActionScript 3.0 - an object-oriented language similar to Java.
• Flash Player 9 - a virtual machine with a tiny footprint that lives inside a Web browser and runs your compiled bytecode (.SWF).
• Command-line compilers and debugger.
• Flex Framework, which includes a library of well-designed GUI component: buttons, tab folders, data grids, tree controls, animated effects, and more.
• Flex Data Services Express (FDS) - a template Web application deployed in a J2EE server to communicate with ActionScript client application run by Flash Player. FDS Express is limited to a single CPU, which makes it useful only for learning purposes.

The following Flex tools require a purchased license:

• Flex Builder - the Eclipse-based IDE
• Charting component
• Flex Data Services Departmental, 24x7, 100 concurrent users
• Flex Data Services Enterprise, 24x7, unlimited users

In a nutshell, the process of creating a basic Flex 2 application consists of the following steps:
1. Design application by adding MXML components like this button:
<mx:Button  label="Place Order" click="processOrder(event)"/>
If you use Flex Builder IDE, you can apply drag-and-drop techniques. Alternatively, you can write the MXML as text.
2. Write the code in ActionScript per your functional specification, for example:
private function processOrder (event:Event):void{
//The business logic goes here
}
3. Compile the code: The Flex compiler automatically converts MXML into ActionScript and creates bytecode output in a form of an SWF file to be run in Flash Player 9 or above. You'll enjoy a fully automatic compilation process if you use the Flex Builder IDE.
4. Deploy the SWF file and the wrapping HTML page in the Web server of your choice. The deployment process and creating the wrapped can be completely transparent if you use the Flex Builder IDE.
More advanced Flex applications can include interaction with the server-side systems through FDS, which provides remote access to server-side Java objects and Java EE components, extensive messaging support (including JMS integration), synchronization with persisted data, and integration with other persistent technologies.

WPF

Recently released Microsoft's Windows Foundation Platform, or WPF uses an XML-based declarative programming language called XAML to create GUIs and C# as a general-purpose programming language. WPF is suitable for creating both RIA and desktop applications. XBAP stands for XAML Browser Application and it's a WPF way of creating RIAs that runs in Internet Explorer.
Microsoft has released a Beta version called WPF/E that will run on some non-Windows platforms (this version uses substitutes C# with JavaScript). While living in a sandbox, XBAP will have access to all .NET 3.0 functionality but WPF/E won't. Common Language Runtime (CLR) is the client's WPF engine.
To create WPF applications, developers can use Microsoft's Visual Studio 2005 IDE with installed .NET 3.0 extensions. The next version of this IDE, called Orcas, will include a visual GUI designer. WPF developers use the same code base for writing XBAP and desktop applications: they just enclose the code sections that aren't allowed in XBAP into the ifdef blocks.
Microsoft XAML code looks similar to Adobe's MXML. Even though today's Flex 2 is a lot more mature than WPF, Microsoft has an established developer base, while Adobe traditionally catered to designers, and its main goal today is to convince enterprise developers (particularly the Java camp) that Flex can be a tool of choice for creating business RIAs.

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