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

/**
 *Bombs travel from right to left in a straight line and disappear at the left edge of the World.
 *Then a new bomb spawns at the right edge. For every evaded bomb the counter's add method is invoked.
 *Upon touching Pac the bomb explodes ending the game.
 */
public class Bomb extends Actor
{

    public void act() 
    {               
        bombMovement();
        bombSpawn();
        removeBomb();
        gameOver();
    } 

    /*
     *right to left movement by the amount specified by the variable bombSpeed 
     */

    public void bombMovement()
    {
        setLocation( getX()-10, getY() );        
    }

    /*
     *adds a new bomb at the left edge of the World at a random y coordinate with a chance of 1/1000 
     */

    public void bombSpawn()
    {
        TurtleWorld turtleWorld = (TurtleWorld) getWorld();

        if ( Greenfoot.getRandomNumber (1000) == 666 )
        {
            turtleWorld.addObject(new Bomb(), turtleWorld.getWidth() -10, Greenfoot.getRandomNumber( turtleWorld.getHeight() ) );
        } 
    }

    /*
     *each time a bomb approaches the left edge of the World it disappears, a new bomb is added to the right edge of the World
     *and the counter is raised by 1
     */

    public void removeBomb()
    {
        TurtleWorld turtleWorld = (TurtleWorld) getWorld();

        if ( getX() <= turtleWorld.getWidth() -turtleWorld.getWidth() +10 )
        {    
            turtleWorld.addObject( new Bomb(), turtleWorld.getWidth() -10, Greenfoot.getRandomNumber( turtleWorld.getHeight() ) );
            turtleWorld.removeObject(this);             
            turtleWorld.getCounter().add(1);            
        }        
    }

    /*
     * upon touching Pac the bomb removes it, changes it's own image to explosion_transp.png and stops the execution
     */

    public void gameOver()
    {
        if ( canSee(Pac.class) )
        {
            eat(Pac.class);
            setImage("explosion_transp.png");
            Greenfoot.stop();
        }
    }

    public boolean canSee(Class clss)
    {
        Actor actor = getOneObjectAtOffset(0, 0, clss);
        return actor != null;        
    }

    public void eat(Class clss)
    {
        Actor actor = getOneObjectAtOffset(0, 0, clss);
        if(actor != null) {
            getWorld().removeObject(actor);
        }
    }
}

if (getWorld() != null && canSee(Pac.class))