I found yet another example of an applet that won't run in a web browser: the Pulse applet in Chapter 9. Java security forbids applets from communicating with any server except the one that served them, and a side-effect is that you can't instantiate ANY DatagramSocket -- such a socket could theoretically receive packets from anywhere, not just the server.

I tried their example in IE4 and got a SecurityException.

It's yet another example where the authors apparently didn't actually try out their code in the real world, which makes the book aggravating to use if you're trying to actually implement something.