The Art and Zen of Web Sites ( http://www.tlc-systems.com/webtips.shtml )
A lot of people are learning how to program in Java and JavaScript. Most of their early efforts seem to be some form of nonstop, repetitive animation that is both annoying and distracting. Some applets keep the page from loading or scrolling properly.
One popular applet overwrites the browser's status display at the bottom of the window, keeping you from viewing the destinations of the links as you move the cursor over them. It also keeps you from seeing the status of the current page as it is loading.
Another popular use for Java is to open a smaller secondary window above the browser. This may prove to be disorienting if your visitors are not ready for it.
If you are developing Java applets, you may wish to wait until you have something more worthwhile before inflicting your early efforts on unsuspecting visitors.
If you make your site so that it can only be viewed with Java or Javascript enabled browsers, you're making a big mistake. An even bigger mistake is to make two versions of your site -- one for Java, and one without.
What will the visitor whose browser does not support Java see at your site? Perhaps an interesting message that the site requires Java. What about the visitor with a Java-capable browser, but with Java disabled? Perhaps a dialog box with an interesting error message.
Some other considerations. Only a fraction of your visitors will have Java-capable browsers. You can test for which browser they're using (and maintain several versions of your site), but some will be using Java-capable browsers with Java turned off due to security concerns. In this case, they may get an interesting error message from the browser's Javascript interpreter.
When your pages are indexed by search engines, they also take an excerpt
from the beginning of the page. If the first thing on your page is a lump
of Javascript code, then this is what the search engine will show as the
description of your page. Perhaps not what you
had in mind.
If, however, you are designing a web-based application to be used on a private Intranet, you may have a valid reason for using one of these new technologies.