public CategoryAxis getDomainAxis(int index) {
        CategoryAxis result = null;
        if (index < this.domainAxes.size()) {
            result = (CategoryAxis) this.domainAxes.get(index);
        }
        if (result == null) {
            Plot parent = getParent();
            if (parent instanceof CategoryPlot) {
                CategoryPlot cp = (CategoryPlot) parent;
                result = cp.getDomainAxis(index);
            }
        }
        return result;