adding score error?

  private int fishEaten;
   private int score;
   
    public Happy()
    {
       fishEaten=0; 
       score=0;
    }

World myWorld = getWorld();
    public void eat()
    {
       if(canSee(Fish.class))
       {
          
           eat(Fish.class);
           
           fishEaten = fishEaten + 1;
           score = fishEaten;
           
         MyWorld jump =(MyWorld)myWorld;
         Counter counter =jump.getCounter();//error here
         counter.addScore();//
          if(fishEaten == 3)
           {
               Greenfoot.stop();
               NewWorld NewWorld = new NewWorld();
               Greenfoot.setWorld(NewWorld);
            }
           
           
        }
        
    }