Every parameter of every public method of every Java API class is documented in the API documentation, and learning to use it is an absolutely essential skill for Java prgrammers http://docs.oracle.com/javase/7/docs/api/
for drawLine it says
> public abstract void drawLine(int x1,
> int y1,
> int x2,
> int y2)
> Draws a line, using the current color, between the points (x1, y1) and (x2, y2) in this graphics context's coordinate system.
> x1 - the first point's x coordinate.
> y1 - the first point's y coordinate.
> x2 - the second point's x coordinate.
> y2 - the second point's y coordinate.