Problem to program a graph which is capable of plotting Quadratic and Linear equations

Hi everyone, i am not new to java. Im an above average programmer and i want to program a graph that is capable of plotting quadratic and Linear equations. The problem is that i dont know how to take care of points that are in decimal. Drawing with pixels cause the points to be so close to one another that you cannot distinguish between them ( say 1.5 and 1.6 ). If anyone can help (maybe to define my own coordinates) please do. Thanks.