Try this:
public void paint (Graphics g) {
Rectangle r = new Rectangle(xPos,yPos,width,height);
g.fillRect(r.getX(), r.getY(), r.getWidth(), r.getHeight());
}
[edit]
// With explicit casting
public void paint (Graphics g) {
Rectangle r = new Rectangle(xPos, yPos, width, height);
g.fillRect(
(int)r.getX(),
(int)r.getY(),
(int)r.getWidth(),
(int)r.getHeight()
);
}