private void notifyBoardCleared() {
   for (Object object : boardStateListenerList.getListeners()) {
     SudokuBoardStateListener listener = (SudokuBoardStateListener) object;
     listener.boardCleared(this);
   }
 }
 protected void notifyCellChanged(Cell cell) {
   for (Object object : boardStateListenerList.getListeners()) {
     SudokuBoardStateListener listener = (SudokuBoardStateListener) object;
     listener.cellChanged(this, cell);
   }
 }
 protected void notifyCellChanged(Cell cell, int newValue, int oldValue) {
   for (Object object : boardStateListenerList.getListeners()) {
     SudokuBoardStateListener listener = (SudokuBoardStateListener) object;
     listener.cellChanged(this, cell, newValue, oldValue);
   }
 }