It would take both a PC based language program and a uploaded Arduino program. The Arduino AVR processor chip's I/O pins cannot be controlled without some kind of uploaded program to read the serial communications commands, interpret them and perform the wanted functions.
Hm, alright. So would you do this, by like... having a switch() statement and interpreting the inputs like that? For example, if I have the Java send a capital A, the switch will read that and know that it needs to, say, raise the brightness from 0 to 255 on a certain light? I guess it would basically have to be some sort of way of wrapping the pinMode and digitalWrite functions. Does that sound at all right?
Wouldn't Firmata allow him to control the Arduino directly from JAVA?
I saw Firmata before but didn't really read into it. Looking at it now, something like sendDigitalPortPair(byte pin, int value) might be what I'm looking for..