int neueHoehe = 50;
    int neueBreite = 50;
    int i = 0;
    boolean ok;
    public void act()
    {
     if(i == 0)
        {
            ok = true;
            i++;
        }
       while(ok == true)
       {
         neueHoehe = (int)(this.getImage().getHeight()*1.1);
         neueBreite = (int)(this.getImage().getWidth()*1.1);
         this.getImage().scale(neueBreite,neueHoehe);
         greenfoot.Greenfoot.delay(3);
        
         if(neueBreite > 150 )
         {
          ok = false;
          neueHoehe = (int)(this.getImage().getHeight()*0.8);
          neueBreite = (int)(this.getImage().getWidth()*0.8);
          this.getImage().scale(neueBreite,neueHoehe);
          greenfoot.Greenfoot.delay(3);
         if(neueBreite < 50)
         {
             ok = true;
         }
       } 
      }
}

GreenfootImage image;
int dSize = 1; // amount in change of size (grow 1 pixel at a time; 

// the line in this method could instead be done in the constructor of the class
// to avoid using this method
protected void addedToWorld(World world)
{
    image = getImage();
}

public void act()
{
    GreenfootImage img = new GreenfootImage(image);
    img.scale(getImage().getWidth()+dSize, getImage.getHeight()+dSize);
    setImage(img);
    if (getImage().getHeight() < 50 || getImage().getHeight() > 150) dSize = -1-dSize;
}