Java can be extended to do anything the machine can do

In theory a Java applet can do anything: manipulate 3D VRML models, play movies, make sounds, you name it. In practice it's a lot more limited. We've already seen one important limitation: an applet has control of its region of the page but no ability to operate elsewhere on the page. But here's a more serious one: an applet can do only what the run time environment allows. Today that's limited to some low level graphics, user interfaces (buttons, menus, text fields and the like), reading and writing files (under strict security guidelines), playing a sound file and some network capabilities.

What's missing? There is no way today to control a VRML model. And what if we want to do more to a sound file than just play it? What if we want to change the volume? Or do a fade in? Or add a reverb? None of these effects exist today in Java's official bag of tricks. (Some are available through undocumented classes that Sun ships with the JDK. Anything undocumented is risky, since there's no support, no guarantee of compatible behavior across platforms and no guarantee that these interfaces won't change. Caveat Emptor.) Anything that Java doesn't support would need to be written in a fully compiled language like C and then made available to the Java run time environment.

And therein lies the real limitation. To do more than Java can do today requires that we do two things: write new libraries that can be used by the Java interpreter; and then make each of those libraries available on every single system that might try to use these new capabilities. An applet is only usable if the capabilities on which it depends are available wherever we want to run them. Because although we can download applets at the moment we want to run them, we can't do the same with the underlying libraries. Java's built-in security makes downloading an applet low in risk; the same can't be said for arbitrary code libraries which do the low level work.

So Java is limited by the pervasiveness of support libraries. We need general 2D and 3D graphics, sound and video manipulation and other multimedia capabilities on every system with a Java-enabled browser. Then we won't be quite so limited. This is the plan for SGI's Cosmo 3D and Sun's Java Media, cross-platform libraries that will extend Java into 3D graphics, sound, video and animation.