/** Looks ahead range locations in current direction
   *  @return the nearest fish in that direction within range (if any);
   *          null if no such fish is found
   */
  private Fish findFish()
  {
    Environment env = environment();
    Location loc = location();
    for (int k = 0; k < range; k++)
    {
      loc = env.getNeighbor(loc, direction());
      if (env.isValid(loc) && !env.isEmpty(loc))
        return (Fish)env.objectAt(loc);
    }
    return null;
  }

  /** Acts for one step in the simulation
   */
  public void act()
  {
    if (!isInEnv())
      return;

    Fish prey = findFish();

    if (prey != null)
    {
      Location preyLoc = prey.location(); 1
      prey.die();
      changeLocation(preyLoc);
    }
    else
      super.act();
  }

1. Save prey's location before you kill the prey.