can coordinate in applet be changed

Hi I am trying to draw a graph 400 by 400 which at the moment means the center is at Y is 200 and X is 200. I know java default is YX 00 at top left corner. My problem is my graph for a linear least fit line has to pass from i.e Y axis 5 (X axis 5) to -5 on Y
and -5 on X axis passing through the center of my graph. How do I change java so the center of my graph is 00. Allowing me to draw lines from positive to negative YX varibles to positive YX.

Thanks if you can advise me, as I know their must be a simply way

lindsey