if (isTouching(Zombies.class))

if (getWorld() != null && isTouching(Zombies.class))

import greenfoot.*;  // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)

/**
 * Write a description of class Bullet here.
 * 
 * @author (your name) 
 * @version (a version number or a date)
 */
public class Bullet extends Actor
{

    /**
     * Act - do whatever the Bullet wants to do. This method is called whenever
     * the 'Act' or 'Run' button gets pressed in the environment.
     */
    public Bullet()
    {

    }

    public void act()
    {
        movement();
        if (getWorld() != null && isTouching(Zombies.class))
        {
            World world = getWorld();
            world.removeObject(this);
            
            
        }
    }

    private void movement()
    {
        move(6);

        if (isAtEdge())
        {
            World world = getWorld();
            if(world != null)
            {
                world.removeObject(this);
                return;

            } 
        }
        if (getWorld() != null && isTouching(Zombies.class))
        {
            
            Counter counter = (Counter) getWorld().getObjects(Counter.class).get(0);
            counter.add(1);
            removeTouching(Zombies.class);
            GreenfootSound eating = new GreenfootSound("Gunshot.mp3");
            if (eating != null)
            {
                eating.play();
            }

        }
        
        
    }
    
    private void repeat()
    {
        
    }
}