public void act() 
    {
        if (isTouching(Bullet.class)){
            world.kills.incrementInteger();
            world.removeObject(this);
            Greenfoot.playSound("explosion.wav");
            return;
        }
        
        if (moveLeft == true) move(2);
        else move(-2);
        
        if (getX() > world.getWidth()-50) moveLeft = false;
        if (getX() < 50) moveLeft = true;
            
       
        
    }