public XSSFCategoryAxis createCategoryAxis(AxisPosition pos) {
long id = axis.size() + 1;
XSSFCategoryAxis categoryAxis = new XSSFCategoryAxis(this, id, pos);
if (axis.size() == 1) {
ChartAxis ax = axis.get(0);
ax.crossAxis(categoryAxis);
categoryAxis.crossAxis(ax);
}
axis.add(categoryAxis);
return categoryAxis;
}