Comp 136 -- Circle-Drawing Algorithms:

public void circleSimple(int xCenter, int yCenter, int radius, Color c)
{
int pix = c.getRGB();
int x, y, r2;

r2 = radius * radius;
for (x = -radius; x <= radius; x++) {
y = (int) (Math.sqrt(r2 - x*x) + 0.5);
raster.setPixel(pix, xCenter + x, yCenter + y);
raster.setPixel(pix, xCenter + x, yCenter - y);
}
}