怎么样画圆用drawstring 参数不能为double
用三角函数怎么画呢

public class circlestar extends Applet{
public static float pi=3.1415926f;

public void paint(Graphics2D a)
{
float i=0;

for(i=0;i<=2*pi;i=i+0.1f)
{
float x=(float) Math.cos(i)*50+60;
float y=(float)Math.sin(i)*50+70;

a.drawString("★", x, y);


}

这个怎么画不出来呢