// extend Critter so he is now a green cannibal

import info.gridworld.actor.Critter;
import info.gridworld.actor.Rock;
import info.gridworld.actor.Actor;
import java.util.ArrayList;
import java.awt.Color;

public class cannibalCritter extends Critter
{
	 public cannibalCritter()
	    {
	        setColor(new Color(0,255,0));
          }

public void processActors(ArrayList actors)
    {
        for (Actor a : actors)
        {
            if (!(a instanceof Rock))
                a.removeSelfFromGrid();
        }
    }
    }
_____________________________________________

import info.gridworld.actor.ActorWorld;
import info.gridworld.actor.Critter;
import info.gridworld.actor.Rock;
import info.gridworld.actor.Bug;
import info.gridworld.actor.Critter;


public class canRunner
{
    public static void main(String[] args)
    {
        ActorWorld world = new ActorWorld();
        world.add(new Bug());
        world.add(new Rock());
        world.add(new Critter());
        world.add(new Critter());
        world.add(new cannibalCritter());
        world.add(new cannibalCritter());
        world.add(new cannibalCritter());
        world.show();
    }
}