// with the following LineOfSight Actor subclass
import greenfoot.*;

public class LineOfSight extends Actor
{
    public LineOfSight()
    { // removes default image (new images are added when needed)
        setImage((GreenfootImage)null);
    }
    
    public boolean isClearBetween(Actor looker, Actor toSee)
    { // checks line of sight from first actor to second actor
        if (looker == null || toSee == null || looker == toSee) return false; // must have two distinct actors
        if (looker.getWorld() == null || looker.getWorld() != toSee.getWorld()) return false; // both actors must be in same world
        if (getWorld() != looker.getWorld()) looker.getWorld().addObject(this, 0, 0); // this actor must be in same world
        setLocation(looker.getX(), looker.getY()); // set at location of first actor
        int dist = (int)Math.hypot(toSee.getX()-looker.getX(), toSee.getY()-looker.getY()); // get distance between actors
        setImage(new GreenfootImage(dist, 2)); // create and set image for this actor
        turnTowards(toSee.getX(), toSee.getY()); // look toward second actor
        move(dist/2); // move in-between the actors
        return getIntersectingObjects(Actor.class).size() == 2; // only the two actors should intersect
    }
}

// class field
private static LineOfSight lineOfSight = new LineOfSight(); // all enemies use the same 'lineOfSight' actor

// in act of enemy class (or in a method called via the act method)
// (after determining if it is time for enemy to shoot)
Actor player = null;
if ( ! getWorld().getObjects(Player.class).isEmpty()) // ensure player is in world
{
    player = (Actor)getWorld().getObjects(Player.class).get(0); // get reference to player
    if (lineOfSight.isClearBetween(this, player)) // check view to player
    {
        // shooting code here
    }
}