if(Greenfoot.KeyDown("left"))
     {
         move(-4);
     }
    if(Greenfoot.KeyDown("right"))
     {
         move(4);
     }
    if(Greenfoot.KeyDown("down"))
     {
         turn(-4);
     }
    if(Greenfoot.KeyDown("up"))
     {
         turn(4);
    }
}