For the player 1 and player 2 thing, you have this:
if (Greenfoot.mouseClicked(this)) {
getWorld().removeObject(this);
you should change it to
if (Greenfoot.mouseClicked(World)) {
getWorld().removeObject(this);
so that they dont remain or use the isEmpty() method
2010/11/2
2010/11/3
2010/11/3