public void scrollUp(){
  setIdleTime(0,false);
  if (!(chatScroll >= (messages.size() - max_nbr_rows))) {
    chatScroll++;
    computeScrollBarOffset();
  }
}

public void scrollUp ( ) { setIdleTime ( 0 , false ) ; if ( ! ( chatScroll >= ( messages . size ( ) - max_nbr_rows ) ) ) { chatScroll ++ ; computeScrollBarOffset ( ) ; } }
scrolls up one line .
