public class Sprite
{
    private int positionX;
    private int positionY;
    private int velocityX;
    private int velocityY;

    // You could put width and height instance variables 
    // here if you thought the generic Sprite should have them.

    public Sprite(int x, int y, int vx, int vy)
    {
        positionX = x;
        positionY = y;
        velocityX = vx;
        velocityY = vy;
    }

    public void step()
    {
        // Move the Sprite one step in the direction and magnitude
        // of its velocity.  Subclasses may want to supplement this
        // behavior (or not) by calling super.step() followed by
        // any desired additional stepping actions.
    }

    public void draw(Graphics g)
    {
        // This will just be a stub, to be overridden in the
        // child classes.  (Or you could draw a default Sprite
        // if you wanted to.  I could see it for testing purposes--
        // maybe a black rectangle or something.)
    }

    /* ... other methods you think the parent should have ... */

    /* ... accessors ... */
}