Ajax doesn't do anything that can't be done with Java, but it's clear
that Ajax _is_ doing things that were never widely done with Java
applets.  Ajax has a relatively lightweight footprint on the client,
particularly for download and first-execution times. It seems that the
marketplace out there prefers one large heavyweight control installed
once, then a very thin scripting language, rather than a medium-weight
Java applet each time.

Java applets also typically provided a different user interface, where
they took over a rectangle of browser window and operated within it
with AWT, whereas Ajax apps are typically light on "GUI features" and
instead work much more with the browser's HTML DOM.  Again there's no
hard and fast rule about one or the other, but popularity seems to
align with practicality more closely for Ajax than for Java applets.

Java applets are also basically unfashionable. A technology of the late
'90s that peaked before the platform could really cope (JVM or network
bandwidth). As a result they've always been regarded as slow, unwieldy
and ugly.  Ajax is almost as old (it really began in '99) but stayed
hidden for some years before it was noticeable. By the time Ajax
emerged into public view, it was already a powerful and well-developed
technology.

No, it doesn't. AJAX is a rehearsal of a very, very old theme:

Client/Server computing

The idea is even much older than the web. With the added twist that the
client code is loaded from remote. But that added twist is also not
exactly new. It is only that the New Bubble 2.0 guys need to find some
poster child "breakthrough technology" to start to pump up the bubble
again.

Regarding Java, Java could do that right from the beginning, and of
course still can do it. The Java technology to deliver and execute
client software in a web-based client/server setup is called Applets.

Applets didn't catch up due to a number of reasons (to early, to slow
for the networks at that time, horrible VM implementations in browsers,
incompatible VMs in browsers, to long startup times, too much nonsense
demo applications (dancing whatever stuff), very few experienced
programmers, to much hype, etc.).

People who want to get rich quick on the 2.0 thing will of course agree.
From a technical point of view it is stone age (in computer terms). It
already smells.

Applets were right from the beginning designed to do client/server
computing the way AJAX does.

The need for a plug-in is an implementation detail. Just like JavaScript
(the lanaguage for AJAX) today is build-in into all mainstream browsers,
there once was a time when a Java VM was build into them.

MS flighted very hard and paid a lot of money in compensation to Sun to
keep Java out of the Windows world and make the Java experience on IE as
painful as possible. The plugin-solution is probably here to stay for a
long time.

/Thomas

Personally I think Ajax is a piece of bailing wire and chewing gum
trying to handle problems that Java or some other secure client side
technology should be doing. However, Microsoft has at every
opportunity done all it could to derail Java. They can't very well
deliberately derail their own piece of garbage, now dignified as
ECMASCRIPT.

It is only a matter of time until a big security scare pulls
JavaScript from corporate desktops.  Then where will everyone be who
built their houses on the JavaScript sand?

Microsoft are fully supporting Ajax. So much so that they have renamed
it Atlas <http://atlas.asp.net/> and, no doubt, are working on ways to
make it totally incompatible with J2EE Application Servers. Meanwhile,
they claim it is "Based on existing standards – DHTML, JScript,
XMLHttp, CSS, etc.".