The Current Time display on the right-hand side near the bottom is a thread that was declared in class called "Clock" which extended Thread. It is instantiated within the applet and the overridden run method inside of the Clock class obtains the current time for display.
The calculator itself has been set up to handle keyboard events, but as far as the program is concerned the focus must be on the applet in general -- the keystrokes won't work otherwise. To do this, click on any empty area of the applet.
On an up note, a dude from Germany told me that he wanted to use my calculator as an example in the Java course he was teaching, and he even asked me to take this page down for the duration of that assignment so that the students couldn't cheat off of my source code! :) I've really appreciated your comments and suggestions, if you have any more, please email me.
Source code is available here.