add random obstacle

// add instance field
int counter;
// add to 'act' method
// or call a method with the following code from the 'act' method
counter = (counter+1)%600; // adjust the 600 to suit (approx 10 secs)
if (counter == 0) setLocation(Greenfoot.getRandomNubmer(getWorld().getWidth()), Greenfoot.getRandomNumber(getWorld().getHeight());

import greenfoot.*;  // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)
import java.awt.Color;
/**
 * Write a description of class Food here.
 * 
 * @author (your name) 
 * @version (a version number or a date)
 */
public class Food extends Actor
{
    int counter;
    /**
     * Act - do whatever the Food wants to do. This method is called whenever
     * the 'Act' or 'Run' button gets pressed in the environment.
     */
    public Food()
    {
        GreenfootImage image;
        image = new GreenfootImage(20, 20);
        image.setColor(Color.RED);
        image.fillRect(0, 0, image.getWidth(), image.getHeight());
        setImage(image);

    }
    
    public void act()
    {
        MyWorld world = (MyWorld)getWorld();
        counter = (counter +1)% 600;
        if( counter == 0)
        {
           
           
               setLocation(Greenfoot.getRandomNumber(getWorld().getWidth()), Greenfoot.getRandomNumber(getWorld().getHeight()));
            
        }
    }
}