public class dolphin extends Actor
{
    private int counter = 0;
    /**
     * Act - do whatever the dolphin wants to do. This method is called whenever
     * the 'Act' or 'Run' button gets pressed in the environment.
     */
    public void act() 
    {
        // Add your action code here.
        move(20);
        if (isAtEdge())
        {
            turn(135+Greenfoot.getRandomNumber(90));
            counter++; //increments everytime dolphin hits edge
            disappear();
        }
    }
      
    /**
     * keep count of how many times object has hit edge.
     * if counter accumelates to == 5 remove object.
     */
    public void disappear()
    {
        if (counter == 8)
        {
            getWorld().removeObject(this); //makes object vanish
        }
    }
    
    public dolphin()
    {
     turn(Greenfoot.getRandomNumber(360));
    }
}

turn(135+Greenfoot.getRandomNumber(90));