How can I find out the number and name of all the parameters passed to my applet?
If implemented in your applet, the getParameterInfo() method of applet will return the names of the parameters your applet accepts. However, I rarely see it implemented, and it doesn't report what is actually in the HTML loader for the applet.
Since you are defining the applet yourself, you should specify what parameters are acceptable. If you need to provide a way of specifying 'infinite' parameters, see How do I create an applet that accepts an unlimited number of parameters?, where you can specify parameters named param1, param2, param3, ..., and the applet will figure out how many are there.