I understand that on some JVMs if a key is held, you will get repeats of keyPressed or keypressed/keyreleased. I really don't want the line visually toggling each time, hence the check for Shift at exactly the point they move the mouse.
well, yes, that's the point of the boolean. as long as the shift key is held, the keyPressed event will be fired about every 10ms (this depends on the oprating system and settings though). since you're using a boolean to check if shift is down, you can check it any time you want regardless of any events going on. You wont notice the constant keyPress events because all thats happening is:
shiftDown = true;
every 10ms, which isnt exactly a bottleneck to worry about.