public Board(int board_size) throws BoardException{
        if(board_size>0 && board_size<100){
            size=board_size;
            fields = new int[size][size];
            for(int i=0; i<size; i++){
                for(int j=0; j<size; j++){
                    fields[i][j]=0;
                }
            }
        } else {
            throw new BoardException();
        }
    }