filling a hexagon(very basic!)

Hey guys, I started learning Java a couple days ago, and my teacher gave me a assignment to make this hexagon that will stretch with the applet and such. I know that int's wont hold decimals but the doubles wont work either for some reason. Now this is the code I am using and the errors it gives are below:

public void paint(Graphics g) {

Graphics2D g2= (Graphics2D)g;

Polygon myPoly = new Polygon();

int a=(getWidth()/2);

int b=(int)a-10*Math.sqrt(3);

myPoly.addPoint(a,0);

myPoly.addPoint(b,10);

myPoly.addPoint(b,30);

g2.fill(myPoly);

and it gives me:

Possible loss of precision on the

int b=(int)a-10*Math.sqrt(3); line

please help me out, thanks in advanced